[Federal Register Volume 70, Number 213 (Friday, November 4, 2005)]
[Proposed Rules]
[Pages 67278-67302]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 05-21793]



[[Page 67277]]

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Part III





Department of Transportation





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Federal Aviation Administration



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14 CFR Part 25



Airplane Performance and Handling Qualities in Icing Conditions; 
Proposed Advisory Circular 25.21-1X, Performance and Handling 
Characteristics in the Icing Conditions Specified in Part 25, Appendix 
C; Proposed Rule and Notice

  Federal Register / Vol. 70, No. 213 / Friday, November 4, 2005 / 
Proposed Rules  

[[Page 67278]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. 2005-22840; Notice No. 05-10]
RIN 2120-AI14


Airplane Performance and Handling Qualities in Icing Conditions

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This action proposes to introduce new airworthiness standards 
to evaluate the performance and handling characteristics of transport 
category airplanes in icing conditions. This proposed action would 
improve the level of safety for new airplane designs when operating in 
icing conditions, and would harmonize the U.S. and European 
airworthiness standards for flight in icing conditions.

DATES: Send your comments on or before February 2, 2006.

ADDRESSES: You may send comments identified by Docket Number FAA-2005-
22840 using any of the following methods:
     DOT Docket Web site: Go to http://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide Regulations and Policies Web site: Go to 
http://www.faa.gov/regulations_policies/ and follow the instructions 
for sending your comments electronically.
     Mail: Docket Management Facility; U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590-001.
     Fax: 1-202-493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For more information on the rulemaking process, see the 
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
http://dms.dot.gov, including any personal information you provide. For 
more information, see the Privacy Act discussion in the SUPPLEMENTARY 
INFORMATION section of this document.
    Docket: To read background documents or comments received, go to 
http://dms.dot.gov at any time or to Room PL-401 on the plaza level of 
the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Don Stimson, FAA, Airplane & Flight 
Crew Interface Branch, ANM-111, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, WA 98055-
4056; telephone: (425) 227-1129; fax: (425) 227-1149, e-mail: 
[email protected].

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. We also 
invite comments relating to the economic, environmental, energy, or 
federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, and 
include supporting data. We ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking. The docket is available for public 
inspection before and after the comment closing date. If you wish to 
review the docket in person, go to the address in the ADDRESSES section 
of this preamble between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. You may also review the docket using the 
Internet at the Web address in the ADDRESSES section.
    Privacy Act: Using the search function of our docket Web site, 
anyone can find and read the comments received into any of our dockets, 
including the name of the individual sending the comment (or signing 
the comment of behalf of an association, business, labor union, etc.). 
You may review DOT's complete Privacy Act statement in the Federal 
Register published on April 11, 2000 (65 FR 19477-78) or you may visit 
http://dms.dot.gov.
    Before acting on this proposal, we will consider all comments we 
receive on or before the closing date for comments. We will consider 
comments filed late if it is possible to do so without incurring 
expense or delay. We may change this proposal in light of the comments 
we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it to you.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Department of Transportation's electronic Docket 
Management System (DMS) Web page (http://dms.dot.gov/search);
    (2) Visiting the Office of Rulemaking's Web page at http://www.faa.gov/avr/arm/index.cfm; or
    (3) Accessing the Government Printing Office's Web page at http://www.gpoaccess.gov/fr/index.html.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, notice number, or amendment number 
of this rulemaking.

Authority for This Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
subtitle VII, part A, subpart III, section 44701, ``General 
requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing minimum 
standards required in the interest of safety for the design and 
performance of aircraft. This regulation is within the scope of that 
authority because it prescribes new safety standards for the design of 
transport category airplanes.

Organization of This NPRM

    Discussion of this proposal is organized under the headings listed 
below. Whenever there is a reference to a document being included in 
the docket for this NPRM, the docket referred to is Docket Number FAA-
2005-22840. A list of acronyms used is included in an appendix located 
at the end of the preamble material, between the regulatory evaluation 
and the text of the proposed amendments. Unless stated otherwise, rule 
sections referenced in this NPRM are part of Title 14, Code of Federal 
Regulations (14 CFR).

I. Executive Summary

    If adopted, this rulemaking would revise certain sections of part 
25 of Title

[[Page 67279]]

14 Code of Federal Regulations (14 CFR). Part 25 contains the 
airworthiness standards for type certification of transport category 
airplanes, but it does not currently include specific requirements for 
airplane performance or handling qualities for flight in icing 
conditions. Although part 25 requires airplanes with approved ice 
protection features to be able to operate safely in icing conditions, 
there is no standard set of criteria defining what ``to safely 
operate'' in icing conditions means in terms of airplane performance 
and handling qualities. Further, because the existing icing regulations 
only address airplanes with ice protection provisions, it is unclear 
what requirements apply in cases where the applicant is seeking to have 
an airplane without an ice protection system certificated for flight in 
icing conditions.
    This notice proposes to amend part 25 by adding a comprehensive set 
of airworthiness requirements that must be met to receive certification 
approval for flight in icing conditions, including specific performance 
and handling qualities requirements, and the ice accretion (that is, 
the size, shape, location, and texture of the ice) that must be 
considered for each phase of flight. These proposed revisions would 
ensure that minimum operating speeds determined during the 
certification of all future transport category airplanes would provide 
adequate maneuver capability in icing conditions for all phases of 
flight and all airplane configurations.
    This notice proposes to require the same airplane handling 
characteristics that apply in non-icing conditions to continue to apply 
in icing conditions. Additionally, a specific evaluation for 
susceptibility to tailplane stall in icing conditions would be added. 
This proposal, if adopted, would harmonize the U.S. and European 
airworthiness standards for flight in icing conditions. It would 
benefit the public interest while retaining or enhancing the current 
level of safety for operation in icing conditions.
    If adopted, this rulemaking would affect manufacturers, modifiers, 
and operators of transport category airplanes (but only for new designs 
or significant changes to current designs that would affect the safety 
of flight in icing conditions). Manufacturers and modifiers may need to 
develop new tests and analyses to determine ice accretions and to 
estimate performance effects for design and certification to address 
icing conditions. Operators may need to develop new or revised 
procedures regarding identification of icing conditions and the 
operation of the ice protection system.
    Service history shows that flight in icing conditions may be a 
safety risk for transport category airplanes. There have been nine 
accidents since 1983 that may have been prevented if this proposed rule 
had been in effect.\1\ The service history that we examined includes 
airplanes certificated to part 25, to its predecessor, the Civil Air 
Regulations (CAR) 4b, or to part 25 icing standards when the airplane 
was certified under part 23. In evaluating the potential for this 
rulemaking to avoid future accidents, we only considered past accidents 
involving tailplane stall or potential airframe ice accretion effects 
on drag or controllability. Accidents related to ground deicing were 
not considered.
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    \1\ These accidents were selected from the National 
Transportation Safety Board's (NTSB) accident database, and are 
discussed in Appendix 3 of this premable.
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    The NTSB has issued several safety recommendations related to 
airframe icing, some of which are addressed, at least in part, by this 
notice. If adopted, this rulemaking would require, during type 
certification, that manufacturers of transport category airplanes:
     Investigate the susceptibility of their airplanes to ice-
contaminated tailplane stall (ICTS);
     Provide for adequate warning on the flight deck of an 
impending stall in icing conditions;
     Show that their airplanes meet the same maneuvering 
capability and handling characteristics requirements in icing 
conditions as in non-icing conditions; and
     Show that their airplanes have adequate performance 
capability in icing conditions.
    As discussed in more detail later, the FAA has tentatively 
determined that this rulemaking would have the following costs and 
benefits over a 45-year analysis period. The cost of the proposed rule 
would be $22.0 million (present value). The FAA assumes the initial 
certification costs of $6.7 million for four new airplane models are 
incurred in year one of a 45-year analysis period. The future 
additional fuel burn expense is estimated to be $59.7 million and would 
be incurred over the 45-year analysis period. The benefits of this 
proposed rule consist of the value of lives saved due to avoiding 
accidents involving part 25 airplanes operating in icing conditions. 
Over the 45-year period of analysis, the potential benefit of the 
proposed rule would be $89.9 million ($23.7 million in present value at 
seven percent).

A. Past Regulatory Approach

    Currently, Sec.  25.1419, ``Ice protection,'' requires transport 
category airplanes with approved ice protection features be capable of 
operating safely within the icing conditions identified in appendix C 
of part 25. This section also requires flight testing and analyses to 
be performed to make this determination. Although an airplane's 
performance capability and handling qualities are important in 
determining whether an airplane can operate safely, part 25 does not 
have specific airplane performance or handling qualities requirements 
for flight in icing conditions, nor does the FAA have a standard set of 
criteria defining what ``to safely operate'' in icing conditions means 
in terms of airplane performance and handling qualities. The proposed 
revisions to part 25 would provide a comprehensive set of harmonized 
requirements for airplane performance and handling qualities to address 
safe operation of transport category airplanes in icing conditions.
    Further, Sec.  25.1419 requires an applicant to demonstrate that 
the airplane can operate safely in icing conditions only when the 
applicant is seeking to certificate ice protection features. It fails 
to address certification approval for flight in icing conditions for 
airplanes without ice protection features.
    In contrast, the European airworthiness standards specifically 
address certification for flight in icing conditions, independent of 
whether the airplane includes ice protection features. In addition, the 
European Joint Aviation Authorities (JAA) proposed additional guidance 
material in the early 1990s to provide criteria for determining whether 
an airplane's performance and handling qualities would allow the 
airplane to operate safely in icing conditions. The JAA's guidance 
material was proposed in draft Advisory Material--Joint (AMJ) 
25.1419.\2\ The JAA's draft AMJ was published on April 23, 1993, as a 
Notice of Proposed Amendment (NPA) 25F-219, ``Flight in Icing 
Conditions--Acceptable Handling Characteristics and Performance 
Effects.''
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    \2\ A JAA AMJ is similar to an FAA advisory circular.
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B. Harmonization of U.S. and European Regulatory Standards

1. Federal Aviation Administration
    Title 14 CFR part 25 contains the U.S. airworthiness standards for 
type certification of transport category airplanes. The part 25 
standards apply to airplanes manufactured within the

[[Page 67280]]

U.S. and to airplanes manufactured in other countries and imported to 
the U.S. under a bilateral airworthiness agreement.
2. Joint Aviation Authorities
    The JAR-25 contains the European airworthiness standards for type 
certification of transport category airplanes. Thirty-seven European 
countries accept airplanes type certificated to the JAR-25 standards, 
including airplanes manufactured in the U.S. that are type certificated 
to JAR-25 standards for export to Europe.
3. European Aviation Safety Agency (EASA)
    The European Community established a new aviation regulatory body, 
EASA, to develop standards to ensure the highest level of safety and 
environmental protection, oversee their uniform application across 
Europe, and promote them internationally. The EASA formally became 
operational for certification of aircraft, engines, parts, and 
appliances on September 28, 2003. The EASA will eventually absorb all 
of the functions and activities of the JAA, including its efforts to 
harmonize the European airworthiness certification regulations with 
those of the U.S.
    The JAR-25 standards have been incorporated into the EASA's 
``Certification Specifications for Large Aeroplanes,'' (CS)-25, in 
similar if not identical language. The EASA's CS-25 became effective 
October 17, 2003.
    The proposals contained in this notice were developed in 
coordination with the JAA. However, since the JAA's JAR-25 and the 
EASA's CS-25 are essentially the same, all of the discussions of these 
proposals relative to JAR-25 also apply to CS-25.
    The FAA's rulemaking proposal, if adopted, would parallel the JAA's 
rulemaking proposal, ``Notice of Proposed Amendment (NPA) 25B, E, F-
332,'' published on June 1, 2002.
    The EASA recently published for comment NPA 16/2004, ``Draft 
Decision of the Executive Director of the Agency on Certification 
Conditions.'' This NPA, published for comment in late 2004, is based on 
the standards that the JAA were expected to adopt.
    Although the FAA, the JAA, and EASA intend to harmonize the 
standards for airplane performance and handling qualities for flight in 
icing conditions, there are some differences between this rulemaking 
proposal and the standards proposed by the JAA and EASA. The 
differences are primarily editorial and are not intended to result in 
significant regulatory differences.

C. Proposal Development--Aviation Rulemaking Advisory Committee

    The FAA, in cooperation with the JAA and representatives of the 
American and European aerospace industries, recognized that a common 
set of standards would not only economically benefit the aviation 
industry, but also maintain a high level of safety. In 1988, the FAA 
and the JAA began a process to harmonize their respective airworthiness 
standards. To assist in the harmonization efforts, the FAA established 
the Aviation Rulemaking Advisory Committee (ARAC) in 1991,\3\ to:
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    \3\ Published in the Federal Register (56 FR 2190), on January 
22, 1991.
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    1. Provide advice and recommendations concerning the full range of 
our safety-related rulemaking activity;
    2. Develop better rules in less overall time using fewer FAA 
resources than are currently needed; and
    3. Obtain firsthand information and insight from interested parties 
regarding proposed new rules or revisions of existing rules.

There are 73 member organizations on the committee, representing a wide 
range of interests within the aviation community.
    We tasked the ARAC Flight Test Harmonization Working Group (FTHWG) 
to recommend to the ARAC new or revised requirements and compliance 
methods related to airplane performance and handling qualities in icing 
conditions.\4\
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    \4\ Published in the Federal Register (56 FR 2190), on June 10, 
1994.
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    The FTHWG reviewed in-service incidents and accidents involving 
transport category airplanes. This review revealed numerous incidents 
resulting from the effects of ice on airplane performance. The same 
review showed that the icing-related accidents resulted from a loss of 
control of the airplane due to the effect of the ice on airplane 
handling qualities. Considering this service history, the FTHWG 
determined that airplanes should generally meet the same handling 
qualities standards in icing conditions that they currently must meet 
for non-icing conditions. In certain areas, however, the FTHWG decided 
that the current handling qualities standards were inappropriate for 
flight in icing conditions. In these areas, the FTHWG developed 
alternative criteria that would apply to icing conditions.
    Since airplane performance degradation was not a causal factor in 
any of the icing-related accidents, the FTHWG concluded that the 
current performance standards already provide some safety margin to 
offset the negative effects of ice accretion. On the basis of this 
service history, the FTHWG decided that the general approach to 
airplane performance in icing conditions used by the JAA in their draft 
AMJ 25.1419 was appropriate and used this approach in its 
recommendations to the FAA. This approach allows a limited reduction in 
airplane performance capability due to ice before the effects of icing 
must be fully taken into account in the performance data provided in 
the Airplane Flight Manual (AFM). Such an approach minimizes the costs 
to manufacturers and operators while increasing the current level of 
safety for flight in icing conditions.
    This proposed rulemaking is based on the FTHWG's report, which ARAC 
approved and forwarded to the FAA, and refers to the ice accretions to 
be used in showing compliance. These ice accretions are defined in a 
new subsection of appendix C to part 25.\5\
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    \5\ The complete text of the FTHWG's report is available at 
http://www.faa.gov/avr/arm/arac/aractasks/fr0404report.pdf. The 
FTHWG preferred the term ``ice accretion'' rather than ``ice shape'' 
because it includes physical characteristics of the ice build-up 
such as texture and surface roughness in addition to its general 
size and shape.
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D. Related Rulemaking Activity

1. Amendment 25-108
    This Amendment, ``1-g Stall Speed as the Basis for Compliance With 
Part 25 of the Federal Aviation Regulations'' (referred to as the 1-g 
stall rule) (67 FR 708112, November 26, 2002) redefines the criteria 
for determining the stall speed for transport category airplanes. The 
stall speed is important because it is used as a reference speed for 
defining minimum operating speeds that provide a safety margin above 
the speed at which the airplane will stall. The previous part 25 
definition of stall speed defined it as the minimum speed reached in a 
stalling maneuver. This definition could result in a stall speed being 
defined that is too low to support the weight of the airplane in level 
flight.
    The recently adopted 1-g stall rule defines the stall speed as the 
speed at which the aerodynamic lift can support the weight of the 
airplane in 1-g flight. The 1-g stall rule also introduces a 
requirement to demonstrate adequate maneuver capability at the minimum 
operating speeds for airplane configurations associated with low speed 
operations around airports. The JAA adopted the same 1-g stall speed 
requirements in Change 15 to JAR-25.

[[Page 67281]]

2. Ice Protection Harmonization Working Group (IPHWG) Recommendations
    The FAA tasked the ARAC to consider whether airplane manufacturers 
or operators should be required to install ice detectors or provide 
some other acceptable way to warn flightcrews of potentially unsafe ice 
accumulations. The ARAC assigned this task to the IPHWG. The IPHWG 
recommended to the ARAC that the FAA adopt an operating rule for 
certain types of airplanes that would require a reliable method of 
informing pilots when to activate the ice protection system as well as 
a way of knowing when ice is accumulating aft of areas protected by the 
ice protection system. The IPHWG is also working on a recommendation 
for a type certification requirement that would identify acceptable 
ways to inform the flightcrew when to activate the ice protection 
system.
    We also tasked the ARAC to:
     Define an icing environment that includes supercooled 
large drop (SLD) icing conditions;
     Recommend requirements to assess the ability of aircraft 
to safely operate in SLD icing conditions, either for the period of 
time necessary to exit or to operate without restriction; and
     Consider mixed phase conditions (a mixture of supercooled 
water droplets and ice crystals) if such conditions are more hazardous 
than the liquid phase icing environment containing supercooled water 
droplets.
    When ARAC finishes its tasks, we expect it to forward to us a 
report containing their recommendations. These recommendations may lead 
to future rulemaking to address SLD icing conditions, but would not 
directly impact this rulemaking.

E. Advisory Material

    In addition to being tasked to recommend new or revised 
requirements related to airplane performance and handling qualities in 
icing conditions, the ARAC FTHWG was tasked to recommend advisory 
material identifying acceptable ways to comply with the proposed new or 
revised requirements. The FTHWG developed a proposed Advisory Circular, 
(AC) 25.21-1X, ``Performance and Handling Characteristics in the Icing 
Conditions Specified in Part 25, Appendix C.'' We are requesting public 
comments on this proposed advisory circular through a separate notice 
of availability in this edition of the Federal Register.

II. Discussion of the Proposals

A. Proof of Compliance (Sec.  25.21)

    We propose to add paragraph (g), to specify the requirements that 
must be met in icing conditions if an applicant seeks certification 
approval for flight in icing conditions. As discussed above, a review 
of icing-related incidents and accidents revealed loss of control to be 
the greatest threat to safety of flight in icing conditions. 
Consequently, the FTHWG identified the existing part 25 requirements 
that could prevent loss of control if they were applied to icing 
conditions. The FTHWG found, and we tentatively agree, that airplanes 
should continue to comply with most of subpart B of part 25 with ice on 
the airplane to ensure safe flight in icing conditions. The subpart B 
regulations that would be excluded by paragraph (g)(1) were determined 
to be beyond what was necessary to determine an airplane's ability to 
operate safely in icing conditions.
    Because the airplane performance and handling qualities 
requirements are flight-related requirements, it is appropriate to 
place the proposed requirements for flight in icing conditions in part 
25, subpart B (Flight) rather than in the current ice protection rule 
in Sec.  25.1419. Section 25.1419 is in subpart F (Equipment), and, 
though it is closely linked with the subpart B requirements proposed in 
this notice, it primarily applies to the ice protection equipment on 
the airplane.
    The proposed subpart B requirements would provide the minimum 
performance and handling qualities requirements corresponding to the 
Sec.  25.1419 requirement that the airplane ``be able to safely operate 
in the continuous maximum and intermittent maximum icing conditions of 
appendix C.'' Additionally, the proposed requirements would supply the 
means for determining, from a performance and handling qualities 
standpoint, whether the ice protection system and its components are 
effective, as required by Sec.  25.1419(b).
    Compliance with the proposed performance and handling qualities 
requirements may be shown by a variety of means that would be evaluated 
during the particular airplane type certification program. These means 
may include flight testing in natural icing conditions or in non-icing 
conditions using artificial ice shapes, wind tunnel testing and 
analysis, engineering simulator testing and analysis, engineering 
analysis, and comparison to previous similar airplanes.
    The proposed requirements would not specifically require 
performance and handling qualities flight testing to be conducted in 
natural icing conditions. However, we expect that for most new airplane 
designs, and for significant changes to existing designs, at least a 
limited set of tests would be flown in natural icing conditions. The 
purpose of these tests would be to confirm the airplane handling 
qualities and performance results found through other means. The 
proposed advisory material will provide guidance on an acceptable 
flight test program, including the specific tests that should be 
conducted in natural icing conditions.
    Historically, flight tests in measured natural icing conditions 
have also been conducted to verify analyses used to generate ice 
accretions for compliance with Sec.  25.1419(b), and to confirm the 
general physical characteristics and location of ice accretions used to 
evaluate airplane performance and handling qualities. This proposed 
rule is not intended to alter this practice or interpretation of Sec.  
25.1419(b). Existing AC 25.1419-1, ``Certification of Transport 
Category Airplanes for Flight in Icing Conditions,'' provides guidance 
on comparing the ice accretions used to evaluate airplane performance 
and handling qualities with those obtained in natural icing conditions.
    Proposed paragraph (g)(1) would apply the same airplane handling 
qualities requirements to flight in icing conditions as are currently 
required for non-icing conditions. Paragraph (g)(1) would also apply 
most of the airplane performance requirements currently required for 
non-icing conditions to flight in icing conditions. The icing 
conditions for showing compliance would be defined in appendix C to 
part 25. These requirements would apply to normal operations of the 
airplane and its ice protection system as specified in the AFM. By 
referencing the AFM, this paragraph would require that this manual 
include the limitations and operating procedures that are specific to 
operating in icing conditions.
    As noted in the introductory discussion, some degradation in 
airplane performance capability would be permitted when showing 
compliance with the requirements for non-icing conditions. The amount 
of performance degradation permitted in each case is identified in the 
discussion of the individual performance regulations.
    Proposed paragraph (g)(2) would prevent the use of different load, 
weight, and center-of-gravity limits for flight in icing, except where 
compliance with the applicable performance requirements impose more 
restrictive weight limits.
    The reason for these proposed requirements is that operation in 
icing

[[Page 67282]]

conditions should be essentially transparent to the flightcrew. There 
should not be any special procedures or methods used for operating in 
icing conditions other than activating ice protection systems. This 
philosophy comes from applying human factors principles to reduce 
operational complexity and flightcrew workload.

B. Stall Speed (Sec.  25.103)

    We propose to revise Sec.  25.103 to require applicants to 
determine stall speeds with ice on the airplane. The proposed Sec.  
25.103(b)(3) adds ice accretion as a variable that must be considered 
when determining stall speeds to use for the different part 25 airplane 
performance standards.
    Determining stall speeds with ice accretions is necessary to 
identify any increase in stall speeds from those determined for non-
icing conditions. The applicant would then compare any change in stall 
speed due to ice accretion with the allowable stall and operating speed 
effects contained in the proposed airplane performance standards to 
determine whether or not airplane performance data must be determined 
specifically for icing conditions.

C. Takeoff (Sec.  25.105)

    We propose to revise Sec.  25.105(a) to add the net takeoff flight 
path described in Sec.  25.115 to the list of airplane takeoff 
performance parameters that must be determined under the conditions 
specified in this paragraph. Additionally, Sec.  25.105(a) would 
specify when compliance must be shown specifically for icing 
conditions.
    We consider the proposed changes necessary to ensure the safety of 
takeoff operations in icing conditions. Ice on the wings and control 
surfaces can reduce the safety margins that currently are provided to 
prevent stalling the airplane. It can also degrade airplane climb 
performance, and cause controllability problems. We acknowledge that 
many transport category airplanes have safely operated in icing 
conditions using takeoff speeds determined for non-icing conditions. We 
agree with the FTHWG, however, that it is in the interest of safety to 
consider the effects of ice accretions on airplane takeoff performance.
    In developing this proposal, the FTHWG and the FAA considered four 
factors:
     Operating rules and practices intended to ensure that 
critical surfaces of the airplane are free of snow or ice before 
beginning a takeoff;
     The use of anti-icing fluids that provide some protection 
from icing during the takeoff;
     Increasing use of ice detectors and deicing/anti-icing 
systems on airplanes that can be operated while the airplane is still 
on the ground; and
     The icing conditions that we propose to use for the 
takeoff flight phase.
    Existing operating rules, Sec. Sec.  91.527(a), 121.629(b), and 
135.227(a), prohibit pilots from taking off with snow or ice adhering 
to the wings or other critical airplane surfaces. Additionally, 
Sec. Sec.  121.629(c) and 135.227(b) require airplane operators to have 
either an approved ground deicing/anti-icing program or conduct a pre-
takeoff contamination check within five minutes before beginning a 
takeoff to ensure that the wings, control surfaces, and other critical 
surfaces are free of frost, ice, or snow. Operators must train the 
pilots on the effects of these contaminants on airplane performance and 
controllability, on how to recognize airplane contamination, and on 
procedures intended to ensure that contamination is removed before 
takeoff.
    Ground deicing/anti-icing programs include the use of deicing/anti-
icing fluids to remove ice and snow and prevent them from reappearing 
on airplane surfaces during freezing precipitation conditions. Although 
these fluids are designed to flow off the airplane during the takeoff 
roll, we expect the fluids to continue to provide some protection 
throughout the takeoff ground run.
    On some older airplane models, the wing ice protection system was 
designed for use in flight and cannot be operated while the airplane is 
on the ground. Yet many of the current generation of airplanes have ice 
protection systems that can be operated while the airplane is on the 
ground. Some of these systems are also coupled with ice detector 
systems that will automatically activate the ice protection system in 
icing conditions. These features tend to reduce the chances that ice 
will adhere to critical airfoil surfaces during airplane ground 
operations in atmospheric icing conditions.
    As discussed later, we propose to revise appendix C of part 25 to 
define atmospheric icing conditions specifically for the takeoff phase 
of flight. These proposed atmospheric icing conditions would apply 
throughout the takeoff path, but are based on the more critical 
conditions that would be expected to occur at the end of the takeoff 
path. These conditions do not include freezing precipitation on the 
ground. At earlier points in the takeoff path, while the airplane is 
closer to the ground, the proposed takeoff icing conditions would be 
conservative, that is, they would predict larger ice accretions than 
would be likely to occur. If these conditions were to actually occur at 
ground level, they would form a freezing fog condition that would 
probably reduce visibility to the point that takeoffs could not be 
made.
    An important part of determining the effects of ice accretion on 
takeoff performance is to decide at what point in the takeoff ice 
accretion is considered to begin. For the purposes of this rulemaking, 
we consider ice accretion to begin when the airplane lifts off the 
runway surface during takeoff.
    Proposed Sec.  25.105(a) would require applicants to determine 
airplane takeoff performance for icing conditions if the ice that can 
accrete during takeoff results in increasing the reference stall speed 
(VSR) or degrading climb performance beyond specified limits. Section 
25.105(a) references all regulations related to the takeoff path. As a 
result, the performance for the entire takeoff path, including takeoff 
speeds and distances, must be determined for icing conditions if the 
stall speed or climb performance degradation limits are exceeded.
    Section 25.105(a)(2)(i) of the proposal would require applicants to 
determine takeoff path performance for icing conditions if the stall 
speed increases by more than 3 knots in calibrated airspeed or 3 
percent due to ice accretions. This proposed requirement would be more 
stringent than the guidance used by the JAA in their draft AMJ 25.1419. 
The draft AMJ allowed up to a 5 knot or 5 percent increase in stall 
speed before the takeoff performance would need to be recomputed for 
icing conditions.
    Several commenters on the AMJ, including us, expressed concern over 
allowing such a large increase in stall speed believing it would result 
in a significant reduction in safety margin between the minimum 
operating speeds and the stall speed. We agree with the FTHWG 
recommendation that a 3 knot or 3 percent increase in stall speeds is 
the maximum that should be permitted before the takeoff performance 
data should be recalculated to consider the effects of icing.
    Also, the JAA's draft AMJ 25.1419 used the effect of ice accretions 
on airplane drag rather than on climb performance to determine when the 
takeoff performance data must be provided for icing conditions. 
However, we agree with the FTHWG recommendation to consider the effect

[[Page 67283]]

of ice accretions in terms of climb performance in Sec.  
25.105(a)(2)(ii) because it would cover more operating variables than 
just the effect of ice on airplane drag.
    The part 25 takeoff climb requirements include a safety margin by 
requiring applicants to determine a net flight path based on the 
airplane's actual climb performance capability reduced by a set value 
that depends on the number of engines on the airplane. Proposed Sec.  
25.105(a)(2)(ii) would require applicants to determine takeoff path 
performance specifically for icing conditions if more than half of this 
safety margin would be lost due to the effects of ice accretion.
    Part 25 divides the takeoff climb performance requirements into 
several segments. To establish the allowable limit for takeoff climb 
performance degradation in icing conditions, Sec.  25.105(a)(2)(ii) 
would consider the effect of ice accretions on just the takeoff climb 
segment defined by Sec.  25.121(b). For most transport category 
airplanes, this segment most often limits the allowable takeoff weight, 
and therefore is the most critical to safety. If the effects of ice 
accretions during the takeoff climb segment defined in Sec.  25.121(b) 
are beyond specified limits, the airplane performance for the entire 
takeoff path must be determined with ice accretions on the airplane. 
This would include from the beginning of the takeoff roll until the 
airplane is at least 1,500 feet above the takeoff surface. Thus, for 
airplanes that would be most affected by ice accretions during the 
takeoff climb, additional safety margins would also be provided for the 
takeoff ground run even though ice accretion is assumed not to begin 
until liftoff.

D. Takeoff Speeds (Sec.  25.107)

    We propose to revise Sec.  25.107(c)(3) and (g) to change the 
reference for maneuver capability considerations from Sec.  25.143(g) 
to Sec.  25.143(h). This is an editorial change due to the 
redesignation of Sec.  25.143(g) to Sec.  25.143(h) proposed below.
    We also propose to revise Sec.  25.107 by adding a new paragraph 
(h). This new paragraph would state that the minimum control speeds 
(VMCG and VMC) and minimum unstick speeds 
(VMU) determined for the airplane in non-icing conditions 
may also be used for the airplane in icing conditions. The 
VMU, VMCG, and VMC speeds are used to 
determine the takeoff speeds V1, VR, and 
V2.
    The minimum unstick speed (VMU) is defined in Sec.  
25.107(d) as the airspeed at and above which the airplane can safely 
lift off the ground and continue the takeoff. Takeoff speeds must be 
established sufficiently above this speed to assure the airplane can 
safely take off considering the variations in procedures and conditions 
that can reasonably be expected in day-to-day operations. Because these 
proposals assume that ice accretion does not begin until liftoff, this 
proposal would allow the VMU speeds for non-icing conditions 
to be used for determining takeoff speeds in icing conditions.
    The ground minimum control speed (VMCG) is used in 
determining the takeoff V1 speed. The takeoff V1 
speed is the highest speed at which the pilot must take the first 
action to be able to safely stop the airplane during a rejected takeoff 
and the lowest speed at which the takeoff can be safely continued after 
an engine failure. Since VMCG, like VMU, occurs 
before the airplane lifts off the runway, the assumption is that ice 
has not yet begun accreting on the airplane. Therefore, this proposal 
would allow the VMCG speeds determined for non-icing 
conditions to be used for determining V1 for icing 
conditions.
    The air minimum control speed, VMC (commonly referred to 
as VMCA), is defined in Sec.  25.149(b) as the airspeed at 
which it is possible to maintain control of the airplane, with no more 
than 5 degrees of bank, when the critical engine is suddenly made 
inoperative. Section 25.107 requires the rotation speed (VR) 
and the takeoff safety speed (V2) to be sufficiently higher 
than VMCA to assure that the airplane will be safely 
controllable if the critical engine fails during the takeoff. Since 
VR occurs before liftoff, like VMU and 
VMCG, this proposal would allow the VMCA speeds 
determined for non-icing conditions to be used for determining 
VR for icing conditions.
    Several concerns must be addressed if we are to allow 
VMCA speeds determined in non-icing conditions to be used to 
determine V2 in icing conditions. Unlike VR, 
V2 occurs after liftoff and ice could have begun accreting 
on the airplane. Ice may accrete at V2 because ice 
protection systems are typically not turned on until the airplane 
climbs more than 400 feet after takeoff. Also, many airplanes do not 
have any ice protection on the vertical stabilizer. These concerns 
could lead to a reduction in the airplane's directional control 
capability if ice accretion occurs. To alleviate these concerns, the 
proposed Sec.  25.143(c) would require applicants to show that 
airplanes are safely controllable and maneuverable at the minimum 
V2 speed with the critical engine inoperative and with the 
ice accretion applicable to the takeoff flight phase.

E. Takeoff Path (Sec.  25.111)

    Currently, Sec.  25.111 defines the takeoff path, describes the 
airplane configuration that applies to each portion of the takeoff 
path, and provides airplane performance requirements that must be met. 
We propose to revise Sec.  25.111 by adding a new paragraph (c)(5) 
stating that the airplane's drag used to determine the takeoff path 
after liftoff would be based on the ice accretions defined in the 
proposed revision to appendix C. To accommodate the addition of the new 
paragraph, the ``and'' at the end of Sec.  25.111(c)(3) would be moved 
to the end of Sec.  25.111(c)(4).
    The takeoff path begins at the start of the takeoff roll and ends 
when the airplane is either 1,500 feet above the takeoff surface, or at 
the altitude at which the transition from the takeoff to the en route 
configuration is completed and the final takeoff speed attained, 
whichever is higher. The takeoff path typically has two distinct climb 
segments: One from the point at which the airplane is 35 feet above the 
runway up to 400 feet, and the other from a height of 400 feet to the 
end of the takeoff path. The proposed changes to Sec.  25.111 would 
identify when the takeoff path must be determined for flight in icing 
conditions and specify the ice accretion that must be used for these 
two climb segments.
    New paragraph (c)(5) would refer back to the proposed Sec.  
25.105(a)(2) to identify when the takeoff path must be determined for 
flight in icing conditions. The ice accretions referenced in new 
paragraph (c)(5) would apply to the airborne portions of the takeoff 
path, since we are assuming that ice accretion does not begin until 
liftoff. If takeoff path performance must be determined for icing 
conditions, then the takeoff path must use the takeoff speeds of the 
proposed Sec.  25.107 for icing conditions, using the ice accretions 
specified in paragraph (c)(5).

F. Landing Climb: All-Engines-Operating (Sec.  25.119)

    We propose to revise Sec.  25.119 by requiring the airplane landing 
climb performance to be determined for both non-icing and icing 
conditions; adding references to the appropriate paragraphs of the 
proposed Sec.  25.125 revision for the landing climb speed to use for 
non-icing and icing conditions; referring to the proposed appendix C 
revision to identify the ice accretion that would be used in 
determining landing climb performance in icing conditions; and changing 
the speed used to show

[[Page 67284]]

compliance with Sec.  25.119 from a speed less than or equal to 
VREF to VREF.
    We consider the approach and landing phases of flight to be the 
flight phases most affected by icing conditions because of the 
potential for descending into and holding in icing conditions prior to 
landing. In addition, service history has shown that the majority of 
icing accidents and incidents occur in the holding, approach, and 
landing flight phases. For these reasons, our policy for the last 40 
years has been for applicants to account for the effects of airframe 
ice accretion in their airplane's approach and landing climb 
performance data provided in the Airplane Flight Manual. (Approach and 
landing climb performance refer to the airplane's climb capability in 
the approach and landing configurations during the approach and landing 
flight phases. Sections 25.121(d) and 25.119 require minimum level of 
approach and landing climb performance to ensure that airplanes can 
abort an approach or landing attempt and safely climb away.) The 
proposed changes to Sec. Sec.  25.119 and 25.121(d) (see below) serve 
to codify this policy.

G. Climb: One-Engine-Inoperative (Sec.  25.121)

    We propose to revise Sec.  25.121 by rearranging paragraphs (b), 
(c), and (d) to specify when the required climb performance must be 
determined for icing conditions; refer to the proposed appendix C 
revision to identify the ice accretion that would be used in 
calculating approach climb performance in icing conditions; and provide 
the conditions under which the approach climb speed must be increased 
to account for the effect of ice accretion.
    Sections 25.121(b) and (c) provide the climb performance 
requirements for the takeoff path segments beginning at the point the 
landing gear is fully retracted and ending at the end of the takeoff 
path. As in the proposed revision to Sec.  25.105, we propose to revise 
Sec.  25.121(b) and (c) to require takeoff climb performance to be 
determined for icing conditions if the effect of ice: (1) Increases the 
stall speed at maximum takeoff weight by more than 3 knots or 3 
percent, or (2) reduces the climb performance determined in Sec.  
25.121(b) by more than half the safety margin provided by the net 
gradient adjustment required by Sec.  25.115.
    Section 25.121(a) provides the climb performance requirements for 
the takeoff path segment beginning at liftoff and ending when the 
landing gear is fully retracted. Since we are assuming that ice 
accretion does not begin until liftoff, only a minimal amount of ice 
could be accreted during this climb segment. Therefore, the proposal 
for Sec.  25.21(g)(1) excludes compliance with Sec.  25.121(a) with ice 
accretions on the airplane.
    We propose revising Sec.  25.121(d) to state when the approach 
climb speed must be adjusted for use in icing conditions. Unlike the 
speeds used in the takeoff path, the need to adjust the approach climb 
speed would not be based on the effect of ice accretions on the 
airplane's stall speed. Instead, the measure for determining whether 
the approach climb speed needs to be adjusted for icing conditions is 
based on the effect of ice accretions on the approach climb speed. If 
the approach climb speed for icing conditions does not exceed the climb 
speed for non-icing conditions by more than the greater of 3 knots 
calibrated airspeed (CAS) or 3 percent VSR, then non-icing 
speeds may be used for calculating approach climb performance for icing 
conditions.
    The existing requirement for determining the approach climb speed 
in non-icing conditions provides applicants some flexibility by only 
specifying the maximum allowable approach climb speed. No lower limit 
is specified and we have accepted approach climb speeds as low as 1.13 
VSR (that is, 13 percent above the reference stall speeds). 
We would accept this same level of flexibility for establishing the 
approach climb speeds in icing conditions. The approach climb speeds 
for icing conditions should also be evaluated to ensure that they 
provide adequate maneuver capability.
    This proposal for the approach climb segment is less stringent than 
the 3 knots or 3 percent VSR standard used for takeoff path 
speeds. For example, if the approach climb speed is 1.25 VSR 
and VSR is 100 knots, 3 percent of the approach climb speed 
is 3.75 knots, while 3 percent of VSR would be only 3 knots. 
The approach climb speed could increase by 3.75 knots without requiring 
this increased approach climb speed to be used for calculating the 
approach climb performance in icing conditions. We consider this small 
alleviation to be acceptable since it is only relative to the need for 
increasing the approach climb speed for icing conditions. The approach 
climb performance must be recalculated with the holding ice accretion 
and presented in the AFM regardless of whether the approach climb speed 
is adjusted for operations in icing conditions.

H. En Route Flight Paths (Sec.  25.123)

    We propose to revise Sec.  25.123(a) by specifying a minimum 
allowable speed for determining en route flight paths, which would 
apply to both icing and non-icing conditions. The proposed speed, 
VFTO, is currently used as the minimum allowable speed for 
the final takeoff.
    Additionally, the proposed revision to Sec.  25.123(b) would state 
when an applicant must determine the en route flight paths specifically 
for icing conditions. Similar to the takeoff path requirements of the 
proposed revision to Sec.  25.111, en route flight path performance 
needs to be specifically determined for icing conditions if the effect 
of ice: (1) Increases the en route speed by more than 3 knots or 3 
percent, or (2) reduces climb performance by more than half the safety 
margin provided by the net gradient adjustment required by Sec.  
25.123(b). The ice accretion to be used would be specified in the 
proposed revision to appendix C.
    The reason for proposing to limit the minimum allowable en route 
climb speed to VFTO to is to prevent applicants from showing 
compliance with Sec.  25.123 by trading altitude for airspeed when 
transitioning from the final takeoff to the en route climb segment. 
This clarifying change is consistent with our original intent for Sec.  
25.123(a).
    Another reason for not allowing an en route climb speed less than 
VFTO is that VFTO is the speed at which the 
maneuver capability requirements contained in the existing Sec.  
25.143(g) must be met in the en route configuration. Allowing an en 
route climb speed lower than VFTO would not ensure that the 
airplane has adequate maneuvering capability during the en route climb 
phase of flight.
    We are not proposing any changes to the two-engine-inoperative en 
route flight path requirements contained in Sec.  25.123(c) for flight 
in icing conditions. We do not expect the pilot to stay in icing 
conditions with one engine inoperative for a long enough duration for 
the failure of a second engine in icing conditions to be an issue.
    En route and takeoff flight paths have similar safety issues. 
Therefore, we are proposing requirements for identifying when en route 
climb flight paths must be determined for icing conditions that are 
similar to those proposed for takeoff flight paths. The only 
significant difference is that for the en route climb paths, a speed of 
1.18 VSR determined with the en route ice accretion of 
proposed appendix C is compared to the en route climb speed selected 
for non-icing conditions instead of comparing stall speeds with and 
without ice accretions.
    The reason for this difference is to provide a more stringent 
requirement

[[Page 67285]]

for airplanes that use the minimum allowable en route climb speed of 
1.18 VSR. (1.18 VSR is the minimum allowable 
value of VFTO prescribed by Sec.  25.107(g)). Airplanes that 
use a higher en route climb speed have a larger speed margin to the 
stall speed and more maneuvering capability in the en route climb phase 
to help offset the negative effects of ice accumulation.
    Due to differences in their methods of generating thrust, 
propeller-driven airplanes generally have better climb performance at 
lower airspeeds than turbojet-powered airplanes. To optimize 
performance, the en route climb speed used for propeller-driven 
airplanes is usually the minimum allowable speed of 1.18 
VSR, while the en route climb speed used for turbojet-
powered airplanes is usually higher. Therefore, the proposed 
requirement would be more stringent for propeller-driven airplanes. We 
consider the increased stringency for propeller-driven airplanes to be 
desirable for the following reasons:
     Propeller-driven airplanes generally have deicing systems 
that cycle on and off, allowing ice to accrete on the protected 
surfaces before removing it. Also, these deicing systems typically do 
not remove all of the ice with each cycle, leaving some residual ice. 
Both of these effects result in drag increases that are generally not 
present on turbojet airplanes that have ice protection systems using 
hot bleed air from the engines.
     Propeller-driven airplanes will likely be subjected to 
increased exposure to icing conditions, due to their slower operating 
speeds, shorter flight lengths, and lower cruising altitudes.

I. Landing (Sec.  25.125)

    We propose to revise Sec.  25.125(a) to identify when the landing 
distance must be determined specifically for icing conditions. The 
proposed requirement would specify that the landing distance must be 
determined for icing conditions if the VREF in icing 
conditions exceeds the VREF in non-icing conditions by more 
than 5 knots CAS. For icing conditions, the landing distance would be 
determined with the landing ice accretion defined in the proposed 
revision to appendix C.
    Additionally, a new paragraph (b) would be added to include the 
landing distance requirements that would be moved from the existing 
paragraph (a). The new paragraph (b) would also set the requirements 
for determining the landing speeds to use in determining the landing 
distances for both icing and non-icing conditions. For icing 
conditions, the landing speed must not be lower than 1.23 
VSR0 with the landing ice accretion on the airplane if that 
speed exceeds the VREF for non-icing conditions by more than 
5 knots CAS.
    The existing paragraphs (b) through (f) would be redesignated as 
(c) through (g).
    Whether landing distances or landing speeds must be determined 
specifically for icing conditions depends on whether VREF 
needs to be increased by more than 5 knots CAS to counteract the effect 
of ice on airplane stall speeds. The reasons behind allowing 
VREF to increase by up to 5 knots CAS in icing conditions 
before requiring landing distance performance to be recomputed for 
icing conditions are:
     As part of the flight testing to demonstrate compliance 
with the landing distance requirements, we typically evaluate airplane 
controllability when landing at speeds lower than the normal landing 
speeds. We usually perform this evaluation at a speed 5 knots below 
VREF to cover inadvertent speed variations that may occur in 
operational service. Plus or minus five knots variation from 
VREF is frequently used as a guideline for evaluating 
expected operational variations in landing speeds.
     Normal approaches in transport category airplanes are 
typically flown at speeds above VREF to provide speed 
margins to account for wind gusts. Although the additional speed should 
be bled off by the time that the airplane is over the landing 
threshold, it may not be. Service history does not indicate any safety 
problems with the resulting longer landing distance.
     Many transport category airplanes are flown at a speed 5 
knots higher than VREF during final approach to counter any 
inadvertent speed loss. Often this additional speed has not been bled 
off before reaching the landing threshold. Again, service history does 
not indicate any safety problems with the resulting longer landing 
distance.
     A 5-knot increase above the VREF speed for non-
icing conditions equates to approximately 3 percent of the 1-g stall 
speed (slightly less than 3 percent for larger airplanes). This is 
consistent with the allowable stall speed increase proposed for the 
takeoff path requirements for icing conditions.
    As a further safety consideration for the VREF speed, 
Sec.  25.125(b)(ii)(c) would require that VREF for icing 
conditions must provide the same maneuvering capability (with ice 
accretions on the airplane) as is currently required at VREF 
for non-icing conditions. This may result in an increase to 
VREF for icing conditions even if this increase is less than 
5 knots.
    The current Sec.  25.125(a)(2), which would be redesignated as 
Sec.  25.125(b)(2)(i), requires VREF for non-icing 
conditions to be not less than the landing minimum control speed, 
VMCL. This existing requirement ensures that adequate 
directional control is available in case an engine fails during a go-
around. Under the proposed new rule, the VMCL determined for 
non-icing conditions would continue to be used for icing conditions. 
This would be similar to the takeoff flight phase, where the takeoff 
minimum control speeds, VMCG and VMCA, determined 
for non-icing conditions would continue to be used for icing 
conditions. Unlike the takeoff case; however, the continued use of the 
non-icing VMCL is not explicitly stated. We consider the 
proposed requirements to adequately address this issue without 
proposing an additional explicit requirement. Section 25.125(b)(2)(ii) 
requires VREF for icing conditions to be not less than 
VREF for non-icing conditions. Under Sec.  25.125(b)(2)(i), 
VREF for non-icing conditions must be not less than 
VMCL for non-icing conditions. Taken together, these two 
proposed requirements would allow the VMCL determined for 
non-icing conditions to continue to be used for icing conditions.
    To assure that using the VMCL determined for non-icing 
conditions will provide safe controllability and maneuverability for 
icing conditions, the proposed Sec. Sec.  25.143(c)(2) and (c)(3) would 
require the applicant to show that the airplane will be safely 
controllable and maneuverable during an approach and go-around and an 
approach and landing, both with the critical engine inoperative. For 
added safety during certification flight testing, these maneuvers may 
be accomplished with a simulated engine failure (as noted in the 
proposed advisory material associated with this proposal).

J. Controllability and Maneuverability--General (Sec.  25.143)

    We propose to revise Sec.  25.143 to add a new paragraph (c) that 
requires the applicant to show that the airplane with ice accretions 
and with the critical engine inoperative is safely controllable and 
maneuverable during takeoff, an approach and go-around, and an approach 
and landing; a new paragraph (i) to identify the ice accretions that 
must be used in showing compliance with Sec.  25.143 in icing 
conditions, and to introduce two specific controllability requirements 
that apply to flight in icing conditions; and a new paragraph (j) to 
specify tests for ensuring that the airplane has adequate 
controllability for flight in icing conditions before the ice

[[Page 67286]]

protection system is activated and performing its intended function of 
removing any ice accretions from protected surfaces.
    In addition, existing paragraphs (c) through (g) would be 
redesignated as paragraphs (d) through (h), and paragraph references in 
the newly designated paragraphs (d), (e), and (f) would be revised 
accordingly.
    The requirements proposed in new paragraph (c) are intended to 
ensure that using the minimum control speeds for non-icing conditions 
would not result in controllability and maneuverability safety concerns 
when the same speeds are used for icing conditions.
    The proposed new paragraph (i)(1) would require compliance with all 
of Sec.  25.143 in icing conditions except paragraphs (b)(1) and (2). 
Sections 25.143(b)(1) and (2) are excepted from icing analysis under 
proposed section 25.21(g).
    These proposed requirements assume a conventional empennage (that 
is, wing/fuselage/tailplane) configuration. Special conditions, issued 
in accordance with Sec.  21.16, may be necessary for certification of 
airplanes with an unconventional empennage configuration.
    Applicants can minimize the number of ice accretions to be tested 
by using one accretion that is shown to be the most critical accretion 
for several flight phases.
    In many cases, a thin, rough, layer of ice (defined as sandpaper 
ice in the proposed revision to appendix C) has been shown to have a 
more detrimental effect on handling qualities for airplanes with 
unpowered control systems than larger ice accretions. The effect of 
sandpaper ice accretions may be more significant than larger ice 
accretions on these airplanes. In some cases, such an accretion has 
resulted in control surface hinge moment reversals that required the 
flightcrew to apply extremely high forces to the controls to regain 
control of the airplane. Applicants would have to consider sandpaper 
ice in showing compliance with the proposed Sec.  25.143(i).
    The proposed paragraph (i)(2) would require applicants to conduct a 
pushover maneuver down to a zero g load factor with the critical ice 
accretion on the airplane. (If the airplane lacks enough elevator power 
to get to a zero g load factor, the maneuver may be ended at the lowest 
load factor obtainable.) The purpose of this proposed requirement is to 
evaluate an airplane's susceptibility to a phenomenon known as ice-
contaminated tailplane stall (ICTS). Ice-contaminated tailplane stall 
can be characterized either by completely stalled airflow over the 
horizontal stabilizer, or by an elevator hinge moment reversal due to 
separated flow on the lower surface of the horizontal stabilizer caused 
by ice accretions on the tailplane.
    Several incidents and accidents have been caused by ICTS. These 
incidents and accidents have typically occurred during landing approach 
when the flightcrew either lowered the flaps or abruptly decreased the 
airplane's pitch attitude. Either of these actions will increase the 
angle-of-attack (AOA) of the local airflow over the tailplane. If there 
is ice on the tailplane, the increased AOA may lead to an ICTS.
    The proposed pushover maneuver increases the AOA on an ice-
contaminated tailplane by inducing a nose down pitch rate. An airplane 
is not susceptible to an ICTS if, during the pushover maneuver:
     The pilot must continue to apply a push force to the pitch 
control throughout the maneuver (that is, the airplane will not 
continue the maneuver to or toward a zero g load factor unless the 
pilot applies a push force to the pitch control); and
     The pilot can promptly recover from the maneuver without 
exceeding 50 pounds of pull force on the pitch control.
    The proposed pushover maneuver evolved from earlier criteria 
developed shortly after a series of incidents and accidents highlighted 
the safety concerns related to ICTS. For example, early ICTS test 
criteria called for executing a pushover to a 0.3 g to 0.4 g load 
factor with a pitch rate of not less than 10 degrees per second in an 
attempt to copy the documented ICTS accident conditions. An aggressive 
pushover to zero g was later found to result in the same combination of 
load factor and pitch rate, but with the advantage of not needing 
sophisticated test instrumentation to perform the test.
    In addition to the pushover maneuver, we propose that applicants 
demonstrate the safety of a sideslip maneuver with an ice-contaminated 
tailplane, since this has been shown to be a more critical ICTS 
triggering maneuver for some airplanes. The proposed Sec.  25.143(i)(3) 
would require that any changes in the force the pilot must apply to the 
pitch control to maintain speed with increasing sideslip angle must 
steadily increase with no force reversals.
    Proposed Sec.  25.143(j) would address airplane controllability 
between the time when the airplane first enters icing conditions and 
when the ice protection system is activated and performing its intended 
function. In developing the controllability criteria proposed in 
paragraph (j), we considered the likely duration of this time period 
and the means that might be used for detecting icing conditions and 
activating the ice protection system. The proposed advisory material 
for part 25, appendix C, part II(e) would provide additional guidance 
for determining the appropriate ice accretion for this testing based on 
the means of ice detection.
    Although activation of the ice protection system is expected to 
occur shortly after entering icing conditions, it may not occur for a 
relatively long time if the method of detecting icing conditions 
depends on the crew visually observing a specified amount of ice 
buildup on some reference surface (for example, windshield wiper, icing 
probe). To address this concern, proposed Sec.  25.143(j)(1) requires 
compliance with all of the requirements of Sec.  25.143 that would 
apply to flight in icing conditions for this method of detecting icing 
conditions. In this case, the ice accretion to be used in showing 
compliance would be the ice accretion that would exist before the ice 
protection system is activated and is performing its intended function.
    For airplanes that use other means of detecting icing conditions, 
the proposed requirements would be less stringent. This reflects the 
expectation that the airplane would fly only briefly in icing 
conditions before activation of the ice protection system. Instead of 
requiring compliance with all of the requirements of Sec.  25.143 that 
apply to flight in icing conditions, Sec.  25.143(j)(2) would require 
only a demonstration that the airplane is controllable in a pull-up 
maneuver up to 1.5 g load factor, and that there is no longitudinal 
control force reversal during a pushover maneuver down to a 0.5 g load 
factor.

K. Stall Warning (Sec.  25.207)

    We propose to revise paragraph (b) to require that the means for 
providing a warning of an impending stall must be the same for both 
icing and non-icing conditions. There would be one exception to this 
general rule. If the means of detecting icing conditions does not 
involve waiting until some specified amount of ice has accreted on a 
reference surface, then the stall warning may be provided by a 
different means during the time from when the airplane first enters 
icing conditions until the ice protection system is activated and is 
performing its intended function.
    We propose to add a new paragraph (e) to specify the stall warning 
margin that the stall warning system must provide in icing conditions. 
The stall

[[Page 67287]]

warning margin is how far in advance the pilot is warned of a potential 
stall. We propose to evaluate the stall warning margin in both straight 
and turning flight while decelerating the airplane at rates of up to 
one knot per second. The pilot must be able to prevent stalling the 
airplane using the same recovery maneuver that would be used in non-
icing conditions, starting the recovery maneuver not less than 3 
seconds after the stall warning begins. Paragraph (e) also specifies 
the ice accretions that would be used for showing compliance.
    We propose to revise paragraph (f) to consist of the existing 
paragraph (e), revised to clarify that the pilot must use the same 
maneuver to demonstrate that the airplane can safely recover from a 
stall in icing conditions as is used for non-icing conditions.
    We propose to add a new paragraph (h) to specify the stall warning 
requirements for the time period when the airplane first enters icing 
conditions until the ice protection system is activated and is 
performing its intended function. The proposed stall warning 
requirements would be different for different means of detecting icing 
conditions and whether or not the stall warning is provided by the same 
means for icing conditions and non-icing conditions.
    Currently, part 25 requires airplanes to provide the flightcrew an 
adequate warning of an impending stall so that the flightcrew can 
prevent the stall. The current requirement does not consider the 
effects of ice accretions on the airplane. With ice accretions on the 
airplane, the airplane may stall sooner (that is, at a higher speed or 
lower AOA), possibly even before the stall warning would occur. For an 
airplane to be approved for flight in icing conditions, we consider it 
necessary to provide an adequate stall warning margin with ice 
accretions on the airplane. For human factors reasons, we also consider 
it necessary for the means of providing the stall warning to be the 
same in icing conditions and non-icing conditions. But as discussed in 
the specific proposal for Sec.  25.207(h), we would allow a limited 
exception to this general requirement.
    In most transport category airplanes, the stall warning is provided 
by a device called a stick shaker, which shakes the control column to 
alert the pilot when the airplane is close to stalling. The proposed 
addition to Sec.  25.207(b) would establish the general requirement for 
the same means for the stall warning in icing conditions and non-icing 
conditions. Section 25.207(b) would, however, allow an exception to the 
general requirement. The conditions for the exception to the general 
requirement would be established in Sec.  25.207(h)(2)(ii).
    The general rule of Sec.  25.207(b) may result in a different stick 
shaker activation point for icing conditions because the airplane may 
stall at a different speed or AOA with ice accretions. In order to 
maintain a safe margin above the stall speed and to provide sufficient 
maneuvering capability, an increase in the minimum operating speeds may 
be needed. Increasing the minimum operating speeds, such as takeoff and 
landing speeds, may result in a cost increase if operators have to 
reduce payload to comply with performance requirements at the higher 
operating speeds.
    These potential cost impacts may be minimized for stall warning in 
icing conditions after the ice protection system has been turned on. 
Then the higher settings for flight in icing conditions would only be 
used if the ice protection system has been activated. The higher 
operating speeds would not be a factor, or cost, in other operations.
    However, this design solution would not protect the airplane during 
the time that the airplane is in icing conditions before activation of 
the ice protection system. To protect the airplane during this time 
period, any changes to the stall warning system settings for potential 
ice accretions would need to be active at all times. This would mean 
that the minimum operating speeds would be increased for both icing and 
non-icing conditions with resulting cost implications.
    To minimize the potential cost impact, while ensuring flight 
safety, the FTHWG examined whether different stall warning requirements 
could be used for flight in icing conditions before activation of the 
ice protection system. Flight in icing conditions before activation of 
the ice protection system is a temporary condition. In most cases, this 
time is expected to be relatively short. In those cases, proposed 
paragraph (h)(2) would allow the stall warning to be provided by a 
different means than is used for non-icing conditions. For example, 
natural airplane buffeting might be used instead of a stick shaker. By 
allowing a different means of stall warning, the need to change the 
stall warning system setting would be minimized.
    However, if the stall warning is provided by a different means than 
for flight in non-icing conditions, the proposal seeks to balance this 
with more stringent flight demonstration requirements. The requirements 
would be more stringent for demonstrating that the pilot can safely 
recover the airplane after a stall warning has occurred. This 
demonstration occurs during the flight tests to show acceptable flight 
characteristics for stall recovery. For the time that the airplane is 
in icing conditions before the ice protections system has been 
activated, if stall warning is provided by a different means than for 
non-icing conditions, it may take longer for the flightcrew to 
recognize the impending stall and take recovery action. Therefore, 
instead of allowing a recovery maneuver to be started one second after 
the onset of stall warning, the recovery maneuver must not begin until 
at least 3 seconds after the onset of stall warning. Paragraph 
(h)(2)(i) of the proposal allows the recovery to start within one 
second of the stall warning. The more stringent three-second 
requirement is contained in the proposed paragraph (h)(2)(ii).
    Additionally, proposed paragraph (h)(2)(ii) would require the 
applicant to show that the airplane has safe handling qualities in case 
the flightcrew does not take suitable recovery action in time to 
prevent stalling. Compliance with the stall characteristics 
requirements of Sec.  25.203 would be required for stalls demonstrated 
using a one knot per second deceleration rate.
    Earlier, we stated that in most cases, flight in icing conditions 
before activation of the icing system is expected to be relatively 
brief. However, if the means of detecting icing conditions and 
activating the ice protection system depends on the flightcrew visually 
identifying a discrete amount of ice on a reference surface (for 
example, one-quarter-inch of ice on the wing's leading edge), then this 
temporary condition may be of a relatively long duration. Therefore, we 
consider it appropriate to apply the same requirements for stall 
warning to this case as are applied to the case of flight in icing 
conditions after the ice protection system is fully active. For this 
case, we propose that the stall warning indication must be provided by 
the same means as in non-icing conditions. Proposed paragraph (h)(1) 
contains this requirement.
    The FTHWG determined that applying the existing stall warning 
margin requirements of Sec.  25.207(c) and (d) to icing conditions 
would be far more stringent than best current practices and would 
unduly penalize designs that have not exhibited safety problems in 
icing conditions. The FTHWG examined whether the stall warning 
requirements of existing Sec.  25.207(c) and (d) could be made less 
stringent for icing conditions without

[[Page 67288]]

compromising safety. The proposed Sec.  25.207(e) resulted from this 
effort.
    In developing the proposed Sec.  25.207(e), the FTHWG determined 
that the types of transport category airplanes involved in icing-
related stall accidents:
     Were equipped with deicing boots that operated cyclically 
(for example, a boot cycle every one to three minutes), and
     Were generally very susceptible to large affects on stall 
speeds from ice accretions during the periods between boot cycles 
(known as intercycle ice).
    The proposed criteria of Sec.  25.207(e), in combination with the 
proposed Sec.  25.207(b), would likely require different stall warning 
system settings for icing conditions and non-icing conditions on future 
airplanes with those characteristics. These proposals would have a 
lesser impact on airplanes without those characteristics. The stall 
warning settings established for the airplane without ice accretions 
may be retained for operation in icing conditions, provided they are 
still adequate to prevent stalling if the pilot does not take any 
action to recover until three seconds after the initiation of stall 
warning. Since all modern conventional transport category airplanes use 
some type of artificial stall warning system (stick shaker or combined 
aural and visual warning), and since three seconds is considered 
adequate time for response by a trained pilot, we agree with the FTHWG 
that this stall warning definition would be acceptable for icing 
conditions.
    The proposed revision of Sec.  25.207(f) would require the pilot to 
use the same stall recovery maneuver during the compliance 
demonstration for icing conditions as is used for non-icing conditions. 
This proposal is based on human factors considerations. In operational 
service, pilots would not be expected to respond differently to a stall 
warning indication in icing conditions versus non-icing conditions.

L. Wind Velocities (Sec.  25.237)

    The proposed revisions to Sec.  25.237(a) would add a requirement 
to establish a safe landing crosswind component for use in icing 
conditions. The proposed revision to paragraph (a) also would state 
that the crosswind component established for takeoff without ice 
accretions may be used for takeoffs conducted in icing conditions.
    For taking off in crosswinds, we consider it unnecessary to 
consider the effect of ice accretions since these proposals assume that 
ice accretions do not begin until liftoff. Therefore, airplanes will 
accrete very little ice, if any, while close to the ground where 
crosswinds are a significant safety concern. Proposed Sec.  
25.237(a)(2) explicitly states that the takeoff crosswind component 
without icing is valid for icing conditions.
    However, the conditions on landing are different. Before landing, 
the airplane may spend a significant amount of time exposed to icing 
conditions. These ice accretions may affect directional control when 
crosswinds are encountered close to the ground. As a result, (a)(3)(ii) 
requires evaluation of the landing crosswind component with ice 
accretion.

M. High-Speed Characteristics (Sec.  25.253)

    We propose to revise Sec.  25.253 by adding a new paragraph (c) to 
define the maximum speed for stability characteristics, VFC/
MFC, for icing conditions. The proposal would permit 
applicants to define a VFC/MFC for icing 
conditions that is different than the VFC/MFC 
defined for non-icing conditions. Additionally, Sec.  25.253(b) would 
be revised to refer to Sec.  25.143(g) rather than Sec.  25.143(f) due 
to the proposed renumbering of Sec.  25.143.
    VFC/MFC is the highest speed at which 
compliance with several airplane handling qualities requirements must 
be shown. The FTHWG's review of historical certification data showed 
that none of the flight tests for airplane handling qualities performed 
with ice accretions were conducted above 300 knots CAS. The air loads 
associated with such high speeds tend to make it difficult to keep 
either artificial or natural ice attached to the airframe to accomplish 
the testing. It also minimizes the possibility of encountering this 
condition in operational service. Therefore, we propose that the 
maximum speed for demonstrating stability characteristics with ice 
accretions is the lower of VFC, 300 KCAS, or any other speed 
at which it can be shown that the airframe will be free of ice.

N. Pilot Compartment View (Sec.  25.773)

    We propose to revise Sec.  25.773(b)(1)(ii) to replace the phrase 
``if certification with ice protection provisions is requested'' with 
``if certification for flight in icing conditions is requested.''
    The proposed change is necessary to be consistent with the proposed 
change to Sec.  25.1419. As discussed in the reason for revising Sec.  
25.1419, compliance with icing-related safety of flight requirements 
should depend on whether the airplane would be approved to operate in 
icing conditions, not on whether the airplane has approved ice 
protection provisions installed.

O. Inlet, Engine, and Exhaust Compatibility (Sec.  25.941)

    We propose to revise the references to Sec. Sec.  25.143(c), (d), 
and (e), contained in paragraph (c) of Sec.  25.941, to read Sec.  
25.143(d), (e), and (f).
    The proposed changes are necessary to maintain references to the 
correct paragraphs of Sec.  25.143 if the changes to Sec.  25.143 being 
proposed by this rulemaking are adopted.

P. Ice Protection (Sec.  25.1419)

    We propose to revise the introductory text of Sec.  25.1419 to 
replace the phrase, ``If certification with ice protection provisions 
is desired * * *'' with ``If certification for flight in icing 
conditions is desired * * *'' The current rule requires an applicant to 
demonstrate an airplane's ability to safely operate in icing conditions 
only when the applicant is seeking to certificate ice protection 
features. It fails to address certification approval for flight in 
icing conditions for airplanes without ice protection features. The 
proposed revision, which would adopt the existing wording from JAR 
25.1419, would require an applicant to demonstrate the airplane's 
ability to safely operate in icing conditions whenever the applicant is 
seeking approval for flight in icing conditions.
    We also propose to simplify the second sentence of Sec.  25.1419 to 
remove redundant wording. This change is editorial in nature and is not 
intended to change the requirement in any way.
    We propose to amend Sec.  25.1419 to incorporate the revised 
introductory text for the following reasons:
     A literal reading of the current Sec.  25.1419 wording 
could imply that the applicant does not have to demonstrate that the 
airplane can be safely operated in icing conditions unless an ice 
protection system is installed.
     The revised text would clarify that any airplane approved 
to fly in icing conditions must be capable of operating in the icing 
conditions of appendix C of part 25 regardless of whether or not the 
airplane has an ice protection system.

Q. Part 25, Appendix C

    We propose to revise appendix C of part 25 to create two 
subsections: Part I to define the atmospheric icing conditions that 
must be considered when showing compliance with the icing-related 
requirements of part 25, and part II to define ice accretions for each 
phase of flight. We also propose to add a definition of the atmospheric 
icing conditions to use specifically for the takeoff phase of flight.

[[Page 67289]]

Proposed Appendix C, Part I
    Proposed appendix C, part I would contain the existing appendix C 
definitions of atmospheric icing conditions. We propose adding a 
definition of ``takeoff maximum icing,'' which is to be used in 
determining ice accretions for the takeoff phase of flight.
Proposed Appendix C, Part II
    Proposed appendix C, part II(a) would contain definitions of the 
ice accretions appropriate to each phase of flight. Proposed appendix 
C, part II(b) would provide options for reducing the number of ice 
accretions to be considered for each phase of flight. Proposed appendix 
C, part II(c) would permit applicants to use, for the airplane 
performance tests, the same ice accretion used for evaluating handling 
characteristics. Proposed appendix C, part II(d) would define the 
conditions for determining the ice accretions for the takeoff phase of 
flight. Proposed appendix C, part II(e) would define what ice accretion 
must be considered prior to normal ice protection system operation.
    One early concern with developing appropriate airplane performance 
and handling qualities requirements for the takeoff phase of flight was 
the atmospheric icing environment close to the ground. The FTHWG 
members expressed significant concerns with using the existing appendix 
C atmospheric icing envelopes for this purpose. The FAA meteorologists 
confirmed that the existing appendix C atmospheric envelopes are not 
generally representative of icing conditions close to the ground.
    In general, for determining the size, shape, location, and texture 
of ice accretions on the airplane, one needs information about the 
atmospheric icing environment, i.e., icing cloud size, cloud liquid 
water content, water droplet size, expressed in terms of the mean 
effective diameter of the droplets, and ambient air temperature.
    We propose to use the following definition of atmospheric icing 
conditions for takeoff maximum icing conditions in appendix C, part 
I(e): An icing cloud extending from ground level to a height of 1,500 
feet above the takeoff surface with a liquid water content of 0.35 
grams/meter 3, water droplets with a mean effective diameter 
of 20 microns, and an ambient temperature of minus 9 degrees Celsius (-
9[deg] C). The following discussion presents the reasons for selecting 
these values.
    Since the takeoff phase of flight is relatively short, generally 
ending at a height of 1,500 feet above the takeoff surface (ref. Sec.  
25.111(a)), we consider it reasonable to assume that the entire takeoff 
phase could be flown within the same icing cloud. Therefore, we propose 
that the takeoff maximum icing conditions would extend from ground 
level to a height of 1,500 feet above the level of the takeoff surface.
    Although measured data for liquid water content at low altitudes 
are sparse, a comparison of data contained in the FAA Technical 
Center's database on inflight icing conditions with theoretical 
predictions suggest a maximum liquid water content within the icing 
cloud of 0.35 grams/meter 3 from ground level up to 1,500 
feet. We propose to use this value within the definition of the maximum 
takeoff icing conditions. This proposed value would also cover the 
potential for dense ground fog at freezing temperatures, which our 
meteorologists stated would expose the airplane to a liquid water 
content of approximately 0.30 grams/meter 3.
    For the size of the water droplets, both industry and FAA icing 
specialists concurred that a mean effective diameter of 20 microns 
would be appropriate for icing conditions occurring near ground level. 
We propose to use this value within the definition of the maximum 
takeoff icing conditions.
    Selection of the ambient temperature for takeoff icing was based on 
theoretical predictions that showed the effect of temperature to 
decrease significantly as the temperature itself decreased. We propose 
to use an ambient temperature for the takeoff icing atmosphere of minus 
9 degrees Celsius (-9[deg] C), the point at which any further decrease 
in temperature had a negligible effect on the resulting ice accretion.
    According to our meteorologists, the amount of water vapor that can 
be held without condensing in a given volume of space depends only on 
the temperature of the gas (water vapor, air, etc.) in that space. It 
does not vary with altitude. Therefore, the proposed takeoff icing 
atmosphere would be equally applicable to all airport runway 
elevations.
    Proposed part II(a) references specific phases of flight and 
defines the critical ice accretions associated with the specific phase 
of flight. In the main body of the rule, various sections require 
evaluation using the ice accretion defined in appendix C. Proposed part 
II(a) contains those definitions. For example, Sec.  25.125(a)(1) 
requires evaluation of landing distance using the ice accretion defined 
in appendix C. To perform the evaluation required by Sec.  
25.125(a)(1), an applicant would use the landing ice definition found 
in paragraph (5) of this section.
    To reduce the number of artificial ice accretions that must be 
considered, proposed part II(b) would permit the ice accretion 
determined for one flight phase to be used in showing compliance with 
the flight requirements of another phase, provided the applicant can 
show it has a more critical effect on the flight parameter being 
evaluated. For example, using the ice accretion determined for the 
holding phase to show compliance with the requirements for the takeoff 
phase will generally have a larger effect on performance and therefore 
be more penalizing than using an ice accretion determined specifically 
for the takeoff phase.
    Proposed part II(c) clarifies that the ice accretion with the most 
adverse effect on handling qualities may also be used during the flight 
test demonstrations of performance as long as any performance 
differences are conservatively taken into account. This proposed 
section is consistent with the intent behind proposed part II(b) to 
reduce the number of ice accretions that must be considered. Unlike 
handling qualities, performance effects between relatively small 
differences in ice accretion generally can be addressed adequately 
through analysis.
    Proposed part II(d) states the assumptions under which the takeoff 
ice accretions are determined. Proposed part II(d) also states that it 
must be assumed that the crew does not take any action to activate the 
ice protection system until the airplane is at least 400 feet above the 
takeoff surface. This requirement is consistent with the existing 
requirement of Sec.  25.111(c)(4) that limits the types of 
configuration changes requiring crew action before reaching 400 feet 
above the takeoff surface.
    We consider it necessary to also take into account the effects of 
any ice accretion that may form on the airplane from the time the 
airplane enters icing conditions until the ice protection system is 
activated and is performing its intended function. The size, shape, 
location, and texture of this ice accretion will depend on: (1) The 
means used to identify that the airplane is in icing conditions (for 
example, the pilot seeing ice accreting on the airplane, an ice 
detector, a combination of freezing temperatures and visible moisture), 
(2) the means and procedures for activating the ice protection system 
(for example, the pilot manually activating the system after a 
specified amount of ice builds up or automatic activation), and (3) the

[[Page 67290]]

system characteristics (for example, the time it takes to effectively 
remove the ice). We propose to define the ice accretion applicable to 
the time period before the ice protection system has been activated and 
is performing its intended function as a period of time in the 
continuous maximum icing conditions of proposed part I of appendix C, 
including:
     The time for recognition,
     A delay time appropriate to the means of ice detection and 
activation of the ice protection system, and
     The time needed for the ice protection system to perform 
its intended function after manual or automatic activation.

III. Discussion of Non-Consensus Issues

    One of the goals of the ARAC process is consensus on the proposed 
recommendations. Due to the variety of interests represented in the 
FTHWG, this goal was not fully achieved. The areas of non-consensus, 
however, were confined to specific details within the proposals, and 
not to the overall need to amend part 25 to address airplane 
performance and handling qualities in icing conditions. The issues for 
which full consensus was not achieved within the FTHWG were:
    1. The requirement that a push force must be needed throughout the 
pushover maneuver proposed in the new Sec.  25.143(i)(2);
    2. Whether the test to evaluate longitudinal handling qualities 
during sideslip maneuvers should be required by regulation as proposed 
in the new Sec.  25.143(i)(3), or should only be included in advisory 
material as one means of showing compliance;
    3. Whether the same airplane performance and handling qualities 
requirements (Sec. Sec.  25.143(j) and 25.207(h)) should always apply 
whenever the means to activate the ice protection system depends on the 
pilot to visually identify when the airplane is in icing conditions; 
and
    4. Whether the proposed revision to appendix C adequately ensures 
that the full range of variables are considered in determining what the 
critical ice accretion is for a particular flight phase.
    Each of these non-consensus issues is discussed in more detail 
below.

A. Non-Consensus Issue 1--Sec.  25.143(i)(2)

    The FTHWG did not reach a consensus on the issue of requiring a 
push force throughout the maneuver down to a zero g load factor (or the 
lowest load factor obtainable if limited by elevator power). Although 
there was consensus that the test maneuver should be performed to zero 
g, the group did not reach a consensus on whether the pilot should be 
required to apply a push force to the longitudinal control system 
throughout the maneuver until a zero g load factor is attained. The 
FTHWG considered two alternatives.
    Alternative 1 was developed by FTHWG members who did not support 
our proposal of requiring a push force to be maintained down to zero g 
load factor in the pushover maneuver. These FTHWG members disagreed 
with the proposal for the following reasons:
     Historically, the pushover test was performed to a 0.5 g 
load factor rather than zero g. For example, as practiced by Transport 
Canada (the Canadian airworthiness regulatory authority), this 
demonstration was done with a high pitch rate. Consequently, there was 
significant overshoot of the 0.5 g load factor, down to approximately 
0.25 g or less. This maneuver was intended to be a controllability test 
beginning with the pilot abruptly pushing on the control column to 
achieve a high nose-down pitch rate, followed by a pull to recover. The 
intent was not to reach a specific g level below 0.5 g, but to show 
that the pilot could perform a satisfactory recovery. This has proven 
to be an acceptable test technique. To date, airplanes evaluated with 
this technique have had a satisfactory safety record in service.
     Since the beginning of the 1980s, the practice of many 
certification authorities has been to require testing to lower load 
factors. This evolved until the introduction of the JAA's NPA 25F-219, 
which not only requires testing to zero g, but also requires a push 
force throughout the maneuver to zero g. A zero-g pushover is 
considered to be an improbable condition, going well beyond any 
operational maneuver, and does not properly represent gusts, pitch 
rate, elevator position, or other factors that may contribute to 
tailplane stalls. Also, since the NPA requirement was developed for a 
specific turboprop, and motivated by service experience on turboprop 
airplanes, other requirements were proposed for other types of 
airplanes.
    For the above reasons, the supporters of alternative 1 to Sec.  
25.143(i)(2) consider that requiring a push force to load factors as 
low as zero g is excessive. Instead, they recommend replacing proposed 
Sec.  25.143(i)(2) with:

    The airplane must be controllable in a pushover maneuver down to 
zero g, or the lowest load factor obtainable if limited by elevator 
power. It must be shown that a push force is required throughout the 
maneuver down to 0.5 g. It must be possible to promptly recover from 
the maneuver without exceeding 50 pounds pull control force.

    Further supporting rationale: FAA Advisory Circular 25-7A, ``Flight 
Test Guide for Certification of Transport Category Airplanes,'' defines 
the boundaries of various flight envelopes. With regard to the minimum 
load factor with flaps down:
     The normal flight envelope (NFE) goes to 0.8 g;
     The operational flight envelope (OFE) goes to 0.5 g; and
     The limit flight envelope (LFE) goes to zero g.
    Conceptually, the boundaries of the OFE are as far as the pilot is 
expected to go intentionally, while the LFE is based on structural or 
other limits that should not be exceeded. Between the OFE and the LFE, 
it is acceptable for degraded handling qualities, but the airplane must 
remain controllable and it must be possible to avoid exceeding the 
limit load factor (see Sec.  25.143(b)).
    Although existing regulations do not allow force reversals (for 
example, from a push force on the control column to a pull force in 
this case) for the en route flight phase, in practice, the 
certification tests for these rules do not cover the full structural 
limit flight envelope. Rather, the certification tests cover a 
reasonable range of load factors sufficient to cover normal operations. 
For example, in the en route configuration, where the limit minimum 
load factor is usually negative 1 g, the JAA's Advisory Circular Joint 
(ACJ) No. 2 to JAR 25.143(f) states: ``* * * assessment of the 
characteristics in the normal flight envelope involving normal 
accelerations from 1 g to zero g, will normally be sufficient.''
    With flaps up, zero g is the midpoint between the limit load factor 
and the trim point. The corresponding points for flaps down are zero g 
for the limit load factor and 0.5 g for the midpoint assessment of 
characteristics. The supporters of alternative 1 to Sec.  25.143(i)(2) 
are concerned that requiring a push force to zero g means that this 
limit load factor will be routinely exceeded in the flight tests used 
to show compliance with the proposed rule.
    The zero-g pushover is not like typical stability tests where it is 
possible to establish steady state conditions and measure a repeatable 
control force. The pushover is an extremely dynamic maneuver lasting 
only a few seconds and involving high pitch rates in both directions. 
There will always be variability due to pilot technique. The pilot may 
pull slightly before reaching zero g to reduce the nose-down pitch rate 
and anticipate the recovery. This

[[Page 67291]]

makes it impossible to distinguish between the force required to reach 
a given g level and the force the pilot applies to track the targeted 
pitch rate. At critical conditions, airplanes that meet the criterion 
suggested in the alternative proposal still require a significant pull 
force to recover.
    Alternative 1 to Sec.  25.143(i)(2) would set a limit of 50 pounds 
on the total control force needed to recover promptly. This would 
ensure that the force that the pilot must exert is low enough so that 
even with only one hand on the pitch control (the other hand might be 
on the thrust levers or another control), the pilot can handle a 
combination of:
     The force to halt the nose-down pitch rate,
     The force due to any hinge moment reversal, and
     The force to establish a satisfactory nose-up pitch rate 
for recovery.
    The 50-pound limit is used for a similar purpose in several other 
rules. The effect of data scatter and variations in pilot technique 
will cause airplanes that are not clearly free of ICTS concerns to 
exceed the 50-pound limit too often, so they will not pass this test.
    The supporters of alternative 1 to Sec.  25.143(i)(2) believe that 
the proposal contained in this rulemaking has the potential for 
adversely affecting an entire class of airplanes--namely light to 
medium business jets with trimmable stabilizers and unpowered 
elevators. Many of these airplanes exhibit a mild control force 
reversal from a push force to a pull force between zero g and 0.5 g.
    Although such a characteristic will not comply with the proposed 
rule, the airplane remains easily controllable. The proposed 
requirement for a push force to be required down to a zero g load 
factor would reduce the stabilizer incidence available for trimming the 
airplane by two to four degrees. This would require either a 20 to 40 
percent larger stabilizer or other design changes to compensate for the 
reduction in stabilizer trim range. The supporters of alternative 1 to 
Sec.  25.143(i)(2) do not believe that the cost of these changes is 
justified by any safety benefit, as these airplanes are not the types 
having ICTS accidents.
    Furthermore, the proposed Sec.  25.143(i)(1) would require that 
sandpaper ice be considered if the elevator is unpowered, regardless of 
the ice protection system. Many of the current business jets are 
equipped with anti-ice systems that prevent ice formation on the 
stabilizer leading edge. Thus, the jets would be evaluated under more 
critical assumptions (that is, with the anti-ice system off) than the 
types that have had accidents.
    Ice-contaminated tailplanes retain normal linear characteristics 
until the onset of flow separation. The separation causes the hinge 
moment coefficient to slope gradually from one level to another over a 
range of 4 to 10 degrees AOA. With the elevator down, the hinge moment 
coefficient changes sign at an AOA in this range, which results in the 
control force reversal from a push to a pull. On a particular business 
jet with a relatively small elevator, this results in a gradually 
increasing pull force from 0 pounds at approximately 0.4 g to 25 pounds 
at zero g.
    On airplanes with large unpowered elevators, especially those with 
long chord lengths, the elevator control forces resulting from a 
stalled tail can be very high. These forces may even be too high for 
the pilots to counteract. For example, assume the elevator dimensions 
of the previous example are scaled up by a factor of 2. The elevator 
chord is then doubled, the area is quadrupled, and the pilot must exert 
8 times as much force on the control to move the elevator. If the 
control force in the previous example were 25 pounds at zero g, the 
control force for this larger elevator would be 200 pounds. These 
examples illustrate how the size and design of elevators for certain 
airplanes determine whether the control forces would be acceptable or 
hazardous. The test criteria recommended for showing compliance with 
the requirements proposed as alternative 1 to Sec.  25.143(i)(2) would 
identify those airplanes with the hazardous characteristics. Therefore, 
the supporters of alternative 1 to Sec.  25.143(i)(2) believe that 
there is no difference in safety between this alternative and our 
proposal.
    Results of the National Aeronautics and Space Administration's 
(NASA) Tailplane Icing Program provide a basis for evaluating whether 
the proposed requirements adequately address the safety concerns. 
Flight tests were conducted in which a test airplane performed a series 
of pushovers and other maneuvers with and without ice accretions. Even 
without ice accretions, reversed control forces were sometimes 
experienced in the pushover maneuvers for some configurations. With the 
ice accretions, control forces exceeding 100 pounds were experienced in 
some of the pushovers although the airplane remained controllable. In 
one test, a departure from controlled flight occurred during a power 
transition with a critical ice accretion and flaps 40 (which is the 
maximum landing flap configuration for this airplane). This event 
involved a sudden nose-down pitch-over from 1-g flight like the ICTS 
accident scenarios. The same ice accretion had degraded pushover 
characteristics to the point that a 50-pound pull was required to 
recover from zero g with flaps 10, and 100 pounds was required with 
flaps 20. Accordingly, the criteria proposed as alternative 1 to Sec.  
25.143(i)(2) provide an adequate safety margin, and would have 
identified the aircraft as unacceptable before it ever got to the flaps 
40 configuration at which it lost control.
    We disagree with the position of the supporters of alternative 1 to 
Sec.  25.143(i)(2) for the following reasons:
    a. Ice contaminated tailplane stall/elevator hinge moment reversal 
has been a significant factor in accidents occurring in icing 
conditions. Rapid and large changes in pitch, significant changes in 
control forces, pilot surprise, and possible disorientation in poor 
visibility that can follow from a tailplane stall/elevator hinge moment 
reversal can result in loss of pitch control. Coupled with the weather 
conditions that lead to ICTS, this loss of control will usually occur 
at low altitude where there is a higher probability of an accident.
    b. Historically, the pushover test was usually performed to 0.5 g 
load factor, although this was often done with a high pitch rate and, 
hence, there was some overshoot of the 0.5 g load factor. A push force 
on the elevator control was required to reach this g level. 
Certification testing and service experience has since shown that 
testing to only to 0.5 g is inadequate, considering the relatively high 
frequency of experiencing 0.5 g in operations. Since the beginning of 
the 1980s, the practice of many certification authorities has been to 
require testing to lower load factors, and the JAA's Notice of Proposed 
Amendment (NPA) 25F-219 requires a push force throughout the maneuver 
to zero g.
    c. Reversal of elevator control force versus normal acceleration is 
not acceptable within the flight envelope. Existing requirements and 
advisory material addressing elevator control force characteristics 
(Sec. Sec.  25.143(f), 25.255(b)(2), and the guidance material to Sec.  
25.143(f)) do not allow force reversals. Furthermore, a survey of FAA, 
JAA, and other flight test personnel showed that a clear majority did 
not favor anything less than a push force on the elevator control to 
zero g.
    Alternative 1 to Sec.  25.143(i)(2) would at least partially 
address the cause of past ICTS accidents. However, the method proposed 
for determining the acceptability of a control force reversal

[[Page 67292]]

is subjective and would lead to inconsistent evaluations. We maintain 
that a push force to zero g with an ice-contaminated tailplane is the 
minimum standard that can be accepted. Zero g is within the flight 
envelope of the airplane and this criterion addresses the need to have 
acceptable handling qualities for operational service when the pilot 
would not expect any control force reversal. Requiring a push force to 
zero g also removes subjectivity in the assessment of the airplane's 
controllability and provides readily understood criteria of 
acceptability. Any lesser standard would not give confidence that the 
problem has been fully addressed.
    Transport Canada proposed the following alternative as a compromise 
between requiring a push force to either zero g or 0.5 g:
    Transport Canada advisory material dating back to the mid-1980s 
specified that applicants must demonstrate  0.5 g applied 
to the longitudinal control. In practice, the demonstration was done in 
a fairly abrupt maneuver that generated a significantly higher 
transient pitch rate than that associated with a steady normal 
acceleration. The minimum normal acceleration obtained was usually 
around 0.25 g or less. It was considered that the pitch rate aspect was 
just as important as the actual normal acceleration in determining 
whether there were unsafe characteristics associated with tailplane 
stall. No pass/fail criteria were provided in the Transport Canada 
guidance except that the characteristics had to be satisfactory.
    The accident record on ice contaminated tailplane stall indicates 
that a significant factor was the pilot's startled reaction to an 
abrupt hinge moment reversal and the magnitude of the control force 
required to recover the airplane to a normal 1 g condition. Alternative 
1 to Sec.  25.143(i)(2) would recognize this controllability issue by 
limiting the amount of pull force required to promptly recover the 
airplane from a zero g condition to a 50-pound pull force. In addition, 
recognizing that positive stability is also important, alternative 1 to 
Sec.  25.143(i)(2) would require a push force down to 0.5 g.
    Accident data available to Transport Canada indicate that aircraft 
involved in incidents and/or accidents incurred a tailplane stall at 
approximately 0.3 g to 0.4 g. Based on this data and Transport Canada's 
past practice, alternative 1 to Sec.  25.143(i)(2) would be acceptable, 
except that the issue of pitch rate is not specifically identified in 
the criteria. Transport Canada recognizes that combining pitch rate 
with a normal acceleration in a requirement is probably too complex, 
especially for the wide range of aircraft designs encompassed by part 
25 and the parallel JAR-25 standards. Thus, Transport Canada considers 
that, if the requirement would only specify a `g' level, then 0.5 g for 
positive stability is inadequate. As a compromise, Transport Canada 
proposes requiring a push force down to a value of 0.25 g as 
alternative 2 to Sec.  25.143(i)(2).
    While it is a compromise between the requirement proposed in this 
rulemaking and alternative 1 (by specifying 0.25 g for the push force 
requirement), we disagree with this alternative because it does not 
fully address the safety concerns throughout the flight envelope. It 
also does not fully address the cost concerns expressed within the 
FTHWG regarding Sec.  25.143(i)(2) as proposed in this rulemaking.
    The Transport Canada alternative recognizes the importance of pitch 
rate. An abrupt nose-down control input is required to reach zero g. We 
consider that testing to zero g, however, ensures that high pitch rates 
are adequately evaluated without the added complication of specifying a 
pitch rate requirement.

B. Non-Consensus Issue 2--Sec.  25.143(i)(3)

    The proposed new Sec.  25.143(i)(3) would add a requirement that 
any changes in longitudinal control force to maintain speed with 
increasing sideslip angle be progressive with no reversals or 
unacceptable discontinuities. The FTHWG did not reach a consensus on 
whether it would be necessary to add a specific regulatory requirement 
to address this issue. The majority of the FTHWG members felt that 
there did not appear to be sufficient data to establish criteria 
specific enough to stand as a regulatory requirement and proposed that 
the issue be addressed through non-regulatory guidance material.
    Anomalies in longitudinal control force during sideslip maneuvers 
have been of concern to some accident investigators and regulatory 
specialists. At one time, we proposed that pushover maneuvers be 
conducted while in sideslips. Transport Canada considered that 
performing sideslips in a pushover maneuver was excessive, but 
recognizing the concern, proposed an additional requirement that would 
specifically assess longitudinal control stick forces while in sideslip 
maneuvers.
    We consider that a consensus was reached on the need to address 
this issue; the only difference appears to be whether it should be 
addressed in advisory material or in the proposed rule. We consider 
that this issue raises important safety concerns that must be addressed 
as a specific evaluation requirement. Therefore, it is appropriate to 
place it in the rule rather than in an AC. We recognize that AC 
material may also be needed to provide guidance on an acceptable means 
of compliance.

C. Non-Consensus Issue 3--Sec. Sec.  25.143(j)(1) and 25.207(h)

    The proposed new Sec. Sec.  25.143(j)(1) and 25.207(h) would apply 
different requirements when different means are used for the pilot to 
visually recognize icing conditions. Compliance with all of the Sec.  
25.143 controllability requirements for non-icing conditions would 
apply if activation of the ice protection system depends on seeing a 
specified ice accretion on a reference surface (for example, on an ice 
accretion probe, or a wing leading edge). However, less stringent 
requirements using a lesser ice accretion would apply to any other 
means of identifying icing conditions, including seeing the first 
indication of an ice accretion on a reference surface.
    The FTHWG did not reach a consensus on the proposed Sec.  
25.143(j)(1). The Air Line Pilots Association (ALPA), which was 
represented in the FTHWG, disagrees with the proposal. The ALPA 
considers visually recognizing the first indication of ice accreting on 
a reference surface to be the same situation as visually recognizing a 
specific amount of ice accretion on a reference surface. To the ALPA, 
both are means of visual recognition that require the flightcrew to 
monitor conditions outside the cockpit. Whenever it is necessary for 
the pilots to check outside the cockpit (which the ALPA does not 
consider to be equivalent to a primary instrument visual scan pattern), 
the ALPA believes that the same basic maneuver capabilities, stall 
protection requirements, and ice accretion amounts should apply.
    The ALPA proposes the following alternative text for Sec.  
25.143(j)(1):
    ``If normal operation of any ice protection system is dependent 
upon visual recognition of ice accretion, the requirements of Sec.  
25.143 are applicable with the ice accretion defined in proposed 
appendix C, part II(e).''
    The ALPA has similar concerns with the proposed Sec.  25.207(h)(1) 
and proposes the following alternative text:
    ``If normal operation of any ice protection system is dependent 
upon visual recognition of ice accretion, the requirements of this 
section, except

[[Page 67293]]

paragraphs (c) and (d), are applicable with the ice accretion defined 
in appendix C, part II(e).''
    We disagree with the alternative proposals for Sec. Sec.  
25.143(j)(1) and 25.207(h)(1).
    The FTHWG found that there are significant differences in the 
aerodynamic effects on an airplane between the two different means of 
visual recognition of icing conditions identified in the ALPA 
alternative proposal discussion. The best example of the means covered 
by Sec. Sec.  25.143(j)(1) and 25.207(h)(1), as proposed in this 
notice, are airplanes with pneumatic deicing boots. The operating 
procedures call for a specified amount of ice build-up before 
activating the ice protection system, a process that is repeated often 
during an icing encounter. In this case, the airplane is assured of 
being operated with some level of aerodynamic degradation before 
activation of the ice protection system.
    The best example of the second type of visual recognition of icing 
conditions are airplane models that are equipped with an ice accretion 
probe in the pilot's field of view outside the airplane. The published 
procedure calls for activating the ice protection system at the first 
indication of ice buildup on the accretion probe. Such accretion 
probes, or an equivalent such as a windshield wiper post, are highly 
efficient ice collectors, and typically will accrete visible ice prior 
to ice accretion on aerodynamic surfaces. Under this means of detecting 
icing conditions, there may be little or no ice buildup on aerodynamic 
surfaces before activation and normal operation of the ice protection 
system, and little or no aerodynamic degradation. These two means of 
visually recognizing that icing conditions are present are distinctly 
different.

D. Non-Consensus Issue 4--Appendix C

    The ALPA representative on the FTHWG did not consider that the 
combination of the proposed regulatory changes and associated proposed 
advisory material provided a definitive enough description of the 
required ice accretions, particularly with regard to the variables that 
must be considered in determining the critical ice accretion for a 
particular flight phase. The ALPA alternative proposal recommends 
adding specific references to ``all flight conditions within the 
operational limits of the airplane'' and ``configuration changes'' to 
the general ice accretion requirements of proposed part II(a) of 
appendix C to ensure that the full range of possible accretion 
locations for atmospheric conditions are considered. The alternative 
text would read:

    Section 25.21(g) states that if certification for flight in 
icing conditions is desired, the applicable requirements of subpart 
B must be met in the icing conditions of appendix C, unless 
otherwise prescribed. The most critical ice accretion in terms of 
handling characteristics and performance for each flight phase must 
be determined, taking into consideration the atmospheric conditions 
of part I of this appendix, and all flight conditions within the 
operational limits of the airplane (for example, configuration, 
configuration changes, speed, angle-of-attack, and altitude). The 
following ice accretions must be determined:

    The NASA research following the Model ATR-72 accident at Roselawn, 
Indiana, in 1994, observed that decreasing AOA causes an increase in 
aft ice accretion limit on the upper surface of an airfoil. Likewise, 
the fact that airflow separation on the negative pressure side (upper 
surface for a typical wing) is caused by ice accretions on the upper 
surface is discussed. Research performed by Dr. Michael B. Bragg and 
others at the University of Illinois has demonstrated significant 
variation in the effects on airfoil aerodynamics of a simulated ice 
accretion depending upon its location on the negative pressure side of 
the airfoil.
    Differing airspeeds and high lift device configurations 
significantly change the AOA and, consequently, the location of the 
stagnation point around which any ice accretion forms on an airfoil. 
For normal operation, this should make no difference on surfaces that 
are protected by the icing system. But for unprotected surfaces, in the 
failure case and for ice that accumulates prior to normal system 
operation, changing the location of ice on the negative pressure side 
of the airfoil may be significant. Procedural restrictions (that is, no 
holding with flaps extended, speed or configuration restrictions in 
case of ice system failure, etc.) could be used to limit the 
configurations necessary to determine the most critical ice accretion. 
However, the full range of possible accumulation locations must be 
considered.
    In their report on the Embraer Model EMB 120 accident at Monroe, 
Michigan, in 1997, the NTSB concluded that:

    The icing certification process has been inadequate because it 
has not required manufacturers to demonstrate the airplane's flight 
handling and stall characteristics under a sufficiently realistic 
range of adverse accretion/flight handling conditions. (Finding 
27)

    The recommendations submitted by the FTHWG, and this proposed rule, 
consider ice accretions for all phases of flight and all configurations 
of high lift devices. The proposed rule would require consideration of 
the effects of the ice accretion during the phases of flight with high 
lift devices extended. The associated proposed advisory material 
specifically recommends that natural icing flight testing with high 
lift devices extended in the approach and landing conditions be 
conducted.
    We do not concur with the alternative discussed above. The research 
referred to above determined the effect on lift and drag of a spoiler-
like shape located at various chord locations of a two dimensional 
airfoil. (A two dimensional airfoil is a wing with an infinite 
wingspan, that is, there are no wingtips. It is common practice for 
wind tunnel testing to use wings that span the test section from one 
wall of the wind tunnel to the other. Results obtained for a two 
dimensional airfoil must usually be adjusted to properly represent a 
real wing.) These data do not support the alternative position because 
no data were presented in the references to connect either this shape 
or its location with airplane flight conditions or icing conditions, 
either inside or outside of proposed appendix C. There were no data 
showing the effect of the shape on an airfoil with high lift devices 
extended.
    The effect of any shape on a two-dimensional airfoil is much larger 
than the effect of a similar shape on a complete airplane with high 
lift devices extended, and the effect of such a shape diminishes with 
increasing airplane size.
    The effect of ice accretions similar to the shapes tested in the 
referenced report were also considered by the FTHWG when it discussed 
ice accreted in conditions outside of proposed appendix C. The majority 
of the FTHWG recommended not including these accretions in the 
recommendations because the only icing design envelope available is 
proposed appendix C.

IV. Rulemaking Notices and Analyses

Paperwork Reduction Act

    The Paperwork Reduction Act of 1995 (44 U.S.C. 3507(d)) requires 
that the FAA to consider the impact of paperwork and other information 
collection burdens imposed on the public. We have determined that there 
are no current new information collection requirements associated with 
this proposed rule.

International Compatibility

    In keeping with U.S. obligations under the Convention on 
International

[[Page 67294]]

Civil Aviation, it is FAA policy to comply with International Civil 
Aviation Organization (ICAO) Standards and Recommended Practices to the 
maximum extent practicable. The FAA has determined that there are no 
ICAO Standards and Recommended Practices that correspond to these 
proposed regulations.

Executive Order 13132, Federalism

    The FAA analyzed this proposed rule under the principles and 
criteria of Executive Order 13132, Federalism. We determined that this 
action would not have a substantial direct effect on the States, on the 
relationship between the national Government and the States, or on the 
distribution of power and responsibilities among the various levels of 
government, and therefore would not have federalism implications.

Regulatory Evaluation, Regulatory Flexibility Determination, 
International Trade Impact Assessment, and Unfunded Mandates Assessment

    This portion of the preamble summarizes the FAA's analysis of the 
economic impacts of a proposed rule amending part 25 of 14 CFR to 
change the regulations applicable to transport category airplanes 
certificated for flight in icing conditions. It also includes summaries 
of the initial regulatory flexibility determination. We suggest readers 
seeking greater detail read the full regulatory evaluation, which is in 
the docket for this rulemaking.
Introduction
    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs that each Federal agency 
propose or adopt a regulation only upon a reasoned determination that 
the benefits of the intended regulation justify its costs. Second, the 
Regulatory Flexibility Act of 1980 requires agencies to analyze the 
economic impact of regulatory changes on small entities. Third, the 
Trade Agreements Act (19 U.S.C. 2531-2533) prohibits agencies from 
setting standards that create unnecessary obstacles to the foreign 
commerce of the United States. In developing U.S. standards, this Trade 
Act requires agencies to consider international standards and, where 
appropriate, to be the basis of U.S. standards. Fourth, the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4) requires agencies to 
prepare a written assessment of the costs, benefits, and other effects 
of proposed or final rules that include a Federal mandate likely to 
result in the expenditure by State, local, or tribal governments, in 
the aggregate, or by the private sector, of $100 million or more 
annually (adjusted for inflation).
    In conducting these analyses, FAA has determined this rule (1) has 
benefits that justify its costs, (2) is not a ``significant regulatory 
action'' as defined in section 3(f) of Executive Order 12866, and is 
not ``significant'' as defined in DOT's Regulatory Policies and 
Procedures; (3) would not have a significant economic impact on a 
substantial number of small entities; (4) would have a neutral impact 
on international trade; and (5) does not impose an unfunded mandate on 
state, local, or tribal governments, or on the private sector. These 
analyses, available in the docket, are summarized below.
Total Benefits and Costs of This Rulemaking
    The estimated cost of this proposed rule is $66.4 million ($22.0 
million in present value at seven percent). The estimated potential 
benefits of avoiding 13 fatalities are $89.9 million ($23.7 million in 
present value at seven percent).
Who Is Potentially Affected by This Rulemaking
     Operators of part 25 U.S.-registered aircraft conducting 
operations under 14 CFR parts 121, 129, 135, and
     Manufacturers of those part 25 aircraft.
Our Cost Assumptions and Sources of Information
    This evaluation makes the following assumptions:
     The base year is 2003.
     This proposed rule is assumed to become a final rule in 2 
years, and will then be effective immediately.
     The production run for newly certificated airplane models 
is 20 years.
     The average life of an airplane is 25 years.
     We analyzed the costs and benefits of this proposed rule 
over the 45-year period (20 + 25 = 45) 2005 through 2049.
     We used a 10-year certification compliance period. For the 
10-year life-cycle period, the FAA calculated an average of four new 
certifications would occur.
     We performed sensitivity analysis on present value 
discount rates of one, three, and the base case seven percent.
     New airplane certifications will occur in year one of the 
analysis time period.
     Value of fatality avoided--$3.0 million (Source: 
``Treatment of Value of Life and Injury In Economic Analysis,'' (FAA 
APO Bulletin, February 2002).)
Benefits of This Rulemaking
    The benefits of this proposed rule consist of the value of lives 
saved due to avoiding accidents involving part 25 airplanes operating 
in icing conditions. We estimate that a total of 13 fatalities could 
potentially be avoided by adopting the proposed rule. We use $3.0 
million as the value of an avoided fatality. Over the 45-year period of 
analysis, the potential benefit of the proposed rule would be $89.9 
million ($23.7 million in present value at seven percent).
Cost of This Rulemaking
    We estimate the costs of this proposed rule to be about $66.4 
million ($22.0 million in present value at seven percent) over the 45-
year analysis period. The total cost of $66.4 million equals the fixed 
certification costs of $6.7 million incurred in the first year plus the 
variable annual fuel burn cost of $59.7 million.
Regulatory Flexibility Determination
    The Regulatory Flexibility Act of 1980 (RFA) establishes ``as a 
principle of regulatory issuance that agencies shall endeavor, 
consistent with the objective of the rule and of applicable statutes, 
to fit regulatory and informational requirements to the scale of the 
business, organizations, and governmental jurisdictions subject to 
regulation.'' To achieve that principle, the RFA requires agencies to 
solicit and consider flexible regulatory proposals and to explain the 
rationale for their actions. The RFA covers a wide-range of small 
entities, including small businesses, not-for-profit organizations and 
small governmental jurisdictions.
    Agencies must perform a review to determine whether a proposed or 
final rule will have a significant economic impact on a substantial 
number of small entities. If the agency determines that it will, the 
agency must prepare a regulatory flexibility analysis as described in 
the Act.
    However, if an agency determines that a proposed or final rule is 
not expected to have a significant economic impact on a substantial 
number of small entities, section 605(b) of the 1980 RFA provides that 
the head of the agency may so certify and a regulatory flexibility 
analysis is not required. The certification must include a statement 
providing the factual basis for this determination, and the reasoning 
should be clear. This proposed rule would not have a significant 
economic impact on a substantial number of small entities.

[[Page 67295]]

International Trade Impact Assessment
    The Trade Agreement Act of 1979 prohibits Federal agencies from 
establishing any standards or engaging in related activities that 
create unnecessary obstacles to the foreign commerce of the United 
States. Legitimate domestic objectives, such as safety, are not 
considered unnecessary obstacles. The statute also requires 
consideration of international standards and, where appropriate, that 
they be the basis for U.S. standards. The FAA has assessed the 
potential effect of this proposed rule and determined that it would 
impose the same costs on domestic and international entities and thus 
have a neutral trade impact.
Unfunded Mandates Assessment
    The Unfunded Mandates Reform Act of 1995 (the Act) is intended, 
among other things, to curb the practice of imposing unfunded Federal 
mandates on State, local, and tribal governments. Title II of the Act 
requires each Federal agency to prepare a written statement assessing 
the effects of any Federal mandate in a proposed or final agency rule 
that may result in an expenditure of $100 million or more (adjusted 
annually for inflation) in any one year by State, local, and tribal 
governments, in the aggregate, or by the private sector; such a mandate 
is deemed to be a ``significant regulatory action.'' The FAA currently 
uses an inflation-adjusted value of $120.7 million in lieu of $100 
million. This proposed rule does not contain such a mandate. The 
requirements of Title II of the Act, therefore, do not apply.

Regulations Affecting Intrastate Aviation in Alaska

    Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat. 
3213) requires the Administrator, when modifying regulations in Title 
14 of the CFR in a manner affecting intrastate aviation in Alaska, to 
consider the extent to which Alaska is not served by transportation 
modes other than aviation, and to establish such regulatory 
distinctions as he or she considers appropriate. Because this proposed 
rule would apply to the certification of future designs of transport 
category airplanes and their subsequent operation, it could, if 
adopted, affect intrastate aviation in Alaska. The FAA therefore 
specifically requests comments on whether there is justification for 
applying the proposed rule differently in intrastate operations in 
Alaska.

Plain Language

    Executive Order 12866 (58 FR 51735, Oct. 4, 1993) requires each 
agency to write regulations that are simple and easy to understand. We 
invite your comments on how to make these proposed regulations easier 
to understand, including answers to questions such as the following:
    Are the requirements in the proposed regulations clearly stated?
     Do the proposed regulations contain unnecessary technical 
language or jargon that interferes with their clarity?
     Would the proposed regulations be easier to understand if 
they were divided into more (but shorter) sections?
     Is the description in the NPRM preamble helpful in 
understanding the proposed regulations?
    Please send your comments to the address specified in the FOR 
FURTHER INFORMATION CONTACT section. [new template uses ADDRESSES]

Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act in the absence of extraordinary circumstances. The FAA has 
determined this proposed rulemaking action qualifies for the 
categorical exclusion identified in paragraph number 312f and involves 
no extraordinary circumstances.

Regulations That Significantly Affect Energy Supply, Distribution, or 
Use

    The FAA has analyzed this NPRM under Executive Order 13211, Actions 
Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). We have determined that it is not 
a ``significant energy action'' under the executive order because it is 
not a ``significant regulatory action'' under Executive Order 12866, 
and it is not likely to have a significant adverse effect on the 
supply, distribution, or use of energy.

V. Appendixes to the Preamble

           Appendix I.--List of Acronyms Used in This Document
 [For your reference and ease of reading, the following list defines the
 acronyms that are used throughout this document. This appendix will not
               appear in the Code of Federal Regulations.]
------------------------------------------------------------------------
               Acronym                             Definition
------------------------------------------------------------------------
AC...................................  Advisory Circular.
ACJ..................................  Advisory Circular Joint (issued
                                        by JAA).
AFM..................................  Airplane Flight Manual.
ALPA.................................  Air Line Pilots Association.
AMJ..................................  Advisory Material Joint (issued
                                        by JAA).
AOA..................................  Angle-of-Attack.
ARAC.................................  Aviation Rulemaking Advisory
                                        Committee.
CAS..................................  Calibrated Airspeed.
CS...................................  Certification Specifications
                                        (EASA airworthiness standards).
EASA.................................  European Aviation Safety Agency.
FAA..................................  Federal Aviation Administration.
FTHWG................................  Flight Test Harmonization Working
                                        Group.
ICTS.................................  Ice-Contaminated Tailplane Stall.
IPHWG................................  Ice Protection Harmonization
                                        Working Group.
JAA..................................  Joint Aviation Authorities.
JAR..................................  Joint Aviation Requirements (JAA
                                        airworthiness standards).
LFE..................................  Limit Flight Envelope.
NASA.................................  National Aeronautics and Space
                                        Administration.
NFE..................................  Normal Flight Envelope.
NPA..................................  Notice of Proposed Amendment
                                        (issued by JAA or EASA).
NPRM.................................  Notice of Proposed Rulemaking.
NTSB.................................  National Transportation Safety
                                        Board.
OFE..................................  Operational Flight Envelope.

[[Page 67296]]

 
SLD..................................  Supercooled Large Drop.
V1...................................  The maximum speed in the takeoff
                                        at which the pilot must take the
                                        first action (for example, apply
                                        brakes, reduce thrust, deploy
                                        speed brakes) to stop the
                                        airplane within the accelerate-
                                        stop distance. V1 also means the
                                        minimum speed in the takeoff,
                                        following a failure of the
                                        critical engine at VEF, at which
                                        the pilot can continue the
                                        takeoff and achieve the required
                                        height above the takeoff surface
                                        within the takeoff distance.
V2...................................  Takeoff Safety Speed. (The target
                                        speed to be reached by the time
                                        the airplane is 35 feet above
                                        the takeoff surface.)
VDF/MDF..............................  Demonstrated Flight Diving Speed.
VEF..................................  Engine Failure Speed. The speed
                                        at which the critical engine is
                                        assumed to fail during takeoff.
VFC/MFC..............................  Maximum Speed for Stability
                                        Characteristics.
VFE..................................  Maximum Flaps Extended Speed.
VFTO.................................  Final Takeoff Speed. The speed at
                                        which compliance is shown with
                                        the final takeoff climb gradient
                                        requirements of Sec.
                                        25.121(c).
VMC..................................  Minimum Control Speed with the
                                        critical engine inoperative.
VMCA.................................  Air Minimum Control Speed.
                                        (Commonly used terminology for
                                        VMC.)
VMCG.................................  Ground Minimum Control Speed.
VMCL.................................  Landing Minimum Control Speed.
VMO/MMO..............................  Maximum Operating Limit Speed.
VMU..................................  Minimum Unstick Speed. The
                                        minimum airspeed at and above
                                        which the airplane can safely
                                        lift off the ground and continue
                                        the takeoff.
VR...................................  Rotation Speed. The speed at
                                        which the pilot first makes an
                                        input to the airplane controls
                                        to rotate the airplane to the
                                        takeoff pitch attitude.
VREF.................................  Landing Reference Speed.
VS 1	g...............................  1-g Stall Speed. The calibrated
                                        airspeed at which aerodynamic
                                        forces alone can support the
                                        airplane in 1-g flight.
VSR..................................  Reference Stall Speed. VSR may
                                        not be less than VS 1	g. For
                                        airplanes with a device that
                                        abruptly pushes the nose down at
                                        a selected angle of attack, (for
                                        example, a stick pusher), VSR
                                        may not be less than 2 knots or
                                        2 percent, whichever is greater,
                                        above the speed at which the
                                        device operates.
VSR0.................................  Reference Stall Speed in the
                                        landing configuration.
------------------------------------------------------------------------


              Appendix 2.--List of Terms Used in This NPRM
   [For the reader's reference and ease of reading, the following list
defines terms that are used throughout this document. This appendix will
             not appear in the Code of Federal Regulations.]
------------------------------------------------------------------------
                       Term                              Definition
------------------------------------------------------------------------
Airfoil...........................................  The shape of the
                                                     wing when looking
                                                     at its profile.
Airplane handling qualities.......................  The response of the
                                                     airplane to control
                                                     inputs as assessed
                                                     primarily by a
                                                     pilot evaluating
                                                     the ease of
                                                     accomplishing
                                                     maneuvering tasks.
                                                     Airplane handling
                                                     qualities refer to
                                                     the stability,
                                                     controllability,
                                                     and maneuverability
                                                     of the airplane.
Airplane performance..............................  The capability of
                                                     the airplane in
                                                     terms of speeds,
                                                     distances, weights,
                                                     flight paths, etc.,
                                                     expressed in terms
                                                     of characteristics
                                                     like takeoff and
                                                     landing distances,
                                                     en route altitude
                                                     capability, climb
                                                     and descent rates,
                                                     flight paths, fuel
                                                     burn, payload
                                                     capability, range,
                                                     etc.
En route ice......................................  The critical ice
                                                     accretion
                                                     appropriate to
                                                     normal operation of
                                                     the ice protection
                                                     system during the
                                                     en route phase of
                                                     flight.
Final takeoff ice.................................  The most critical
                                                     ice accretion
                                                     appropriate to
                                                     normal operation of
                                                     the ice protection
                                                     system during the
                                                     final takeoff
                                                     segment. Ice
                                                     accretion is
                                                     assumed to start at
                                                     liftoff in the
                                                     takeoff maximum
                                                     icing conditions of
                                                     14 CFR part 25,
                                                     appendix C, part 1,
                                                     paragraph (c).
Force reversal....................................  A reversal in the
                                                     direction of the
                                                     force that the
                                                     pilot needs to
                                                     apply to perform a
                                                     specified maneuver
                                                     or achieve a
                                                     specified load
                                                     factor. For
                                                     example, in a
                                                     maneuver to reduce
                                                     the load factor, a
                                                     push force on the
                                                     pitch control is
                                                     initially needed to
                                                     begin the maneuver,
                                                     but changes to a
                                                     pull force as the
                                                     load factor is
                                                     reduced.
Holding ice.......................................  The critical ice
                                                     accretion
                                                     appropriate to
                                                     normal operation of
                                                     the ice protection
                                                     system during the
                                                     holding phase of
                                                     flight.
Hinge moment......................................  The rotational force
                                                     about the hinge of
                                                     a control surface.
                                                     Depending on the
                                                     design of the
                                                     airplane's flight
                                                     control system,
                                                     large hinge moments
                                                     can result in large
                                                     forces at the
                                                     pilot's control,
                                                     and hinge moment
                                                     reversals can
                                                     result in forces
                                                     reversals.
Ice-contaminated tailplane stall..................  Ice accretions on
                                                     the tailplane
                                                     leading to either
                                                     completely stalled
                                                     airflow over the
                                                     horizontal
                                                     stabilizer, or an
                                                     elevator hinge
                                                     moment reversal due
                                                     to separated flow
                                                     on the lower
                                                     surface of the
                                                     horizontal
                                                     stabilizer.
Landing ice.......................................  The critical ice
                                                     accretion
                                                     appropriate to
                                                     normal operation of
                                                     the ice protection
                                                     system during the
                                                     landing phase of
                                                     flight. This is
                                                     usually the same as
                                                     holding ice.
Load factor.......................................  The lift divided by
                                                     the weight,
                                                     expressed in units
                                                     of gravity, or
                                                     ``g.'' For example,
                                                     in straight and
                                                     level flight, the
                                                     lift equals the
                                                     weight and the load
                                                     factor is 1 g.
Pushover maneuver.................................  A maneuver resulting
                                                     from the pilot
                                                     applying a push
                                                     force to the
                                                     airplane pitch
                                                     control to pitch
                                                     the airplane's nose
                                                     down.
Sandpaper ice.....................................  A thin, rough layer
                                                     of ice.
Stall.............................................  Loss of lift caused
                                                     by the airflow
                                                     becoming detached
                                                     from the upper
                                                     surface of a
                                                     lifting surface
                                                     such as a wing or
                                                     tailplane.

[[Page 67297]]

 
Takeoff ice.......................................  The critical ice
                                                     accretion
                                                     appropriate to
                                                     normal operation of
                                                     the ice protection
                                                     system during the
                                                     takeoff phase of
                                                     flight, assuming
                                                     accretion starts at
                                                     liftoff in the
                                                     takeoff maximum
                                                     icing conditions of
                                                     14 CFR part 25,
                                                     appendix C, part 1,
                                                     paragraph (c).
Tailplane.........................................  The horizontal wing
                                                     attached to the
                                                     tail assembly of
                                                     the airplane.
------------------------------------------------------------------------

Appendix 3: Relevant NTSB Recommendations

    If adopted, this rulemaking would respond to the following 
National Transportation Safety Board (NTSB) Safety Recommendations.
    1. Safety Recommendation A-91-87. ``Amend the icing 
certification rules to require flight tests wherein ice is 
accumulated in those cruise and approach flap configurations in 
which extensive exposure to icing conditions can be expected, and 
require subsequent changes in configuration, to include landing 
flaps.'' [complete text available in the docket]
    This safety recommendation resulted from an accident on December 
26, 1989, at Pasco, Washington, where the airplane stalled due to 
ice-contamination on the tailplane.\6\ The radar data revealed that 
the airplane was in the clouds in icing conditions for almost 9\1/2\ 
minutes. The NTSB determined that the probable cause of this 
accident was the flightcrew's decision to continue an unstabilized 
ILS approach that led to a stall, most likely of the horizontal 
stabilizer, and loss of control at low altitude. Contributing to the 
stall and loss of control was the accumulation of airframe ice that 
degraded the aerodynamic performance of the airplane.\7\ The 
airplane was destroyed and the two pilots and all four passengers 
received fatal injuries. As discussed in more detail later, this 
notice proposes to require applicants to demonstrate during type 
certification that their airplane is not susceptible to ice-
contaminated tailplane stall.
---------------------------------------------------------------------------

    \6\ United Express flight 2415 (Sundance 415), a British 
Aerospace BA-3101 Jetstream, operated by NPA Inc., (NPA is the name 
of the airline and is not an abbreviation).
    \7\ ``Effect of Ice on Aircraft Handling Characteristics (1984 
Trials),'' Jetstream 31--G-JSSD, British Aerospace Flight Test 
Report FTR.177/JM, dated May 13, 1985.
---------------------------------------------------------------------------

    2. Safety Recommendation A-98-94. ``Require manufacturers of all 
turbine-engine driven airplanes (including the EMB-120) to provide 
minimum maneuvering airspeed information for all airplane 
configurations, phases, and conditions of flight (icing and non-
icing conditions); minimum airspeeds also should take into 
consideration the effects of various types, amounts, and locations 
of ice accumulations, including thin amounts of very rough ice, ice 
accumulated in supercooled large droplet icing conditions, and 
tailplane icing.'' [complete text available on the NTSB Web site at: 
http://ntsb.gov/Recs/letters/1998/A98_88_106.pdf]
    This safety recommendation resulted from an accident on January 
9, 1997, near Monroe, Michigan.\8\ In that accident, the flightcrew 
were attempting a turning maneuver and did not know there was ice on 
the wing's leading edge. With the degraded aerodynamics due to the 
ice on the wing's leading edge, the airplane was at too low an 
airspeed to conduct the turning maneuver without stalling. This 
caused a rapid descent after an uncommanded roll excursion, 
resulting in a crash. The airplane was destroyed and the 2 flight 
crewmembers, 1 flight attendant, and 26 passengers all died. The 
NTSB determined that the probable cause of this accident was the 
FAA's failure to establish adequate aircraft certification standards 
for flight in icing conditions, and to require the establishment of 
adequate minimum airspeed for icing conditions.\9\
---------------------------------------------------------------------------

    \8\ Comair flight 3272, Empresa Brasileira de Aeronautica, S/A 
(Embraer) EMB-120, operated by COMAIR Airlines, Inc.
    \9\ National Transportation Safety Board, 1998. ``In-Flight 
Icing Encounter and Uncontrolled Collision With Terrain, Comair 
Flight 3272, Embraer EMB-120RT, N265CA, Monroe, Michigan, January 9, 
1997.'' Aircraft Accident Report NTSB/AR-98/04. Washington, DC.
---------------------------------------------------------------------------

    As discussed in more detail later, this notice proposes to 
require applicants to demonstrate during type certification that 
their airplane has adequate maneuvering capabilities in icing 
conditions. The requirements added to part 25 by the 1-g stall rule 
\10\ and the requirements proposed in this NPRM would ensure that 
the minimum operating speeds determined during the certification of 
all future transport category airplanes provide adequate maneuver 
capability in both non-icing and icing conditions.
---------------------------------------------------------------------------

    \10\ Docket No. FAA-2002-13982, published in the Federal 
Register (67 FR 70812, November 26, 2002).
---------------------------------------------------------------------------

    3. Safety Recommendation A-98-96. ``Require the manufacturers 
and operators of all airplanes that are certificated to operate in 
icing conditions to install stall warning/protection systems that 
provide a cockpit warning (aural warning and/or stick shaker) before 
the onset of stall when the airplane is operating in icing 
conditions.'' [complete text available on the NTSB Web site at: 
http://ntsb.gov/Recs/letters/1998/A98_88_106.pdf]
    This safety recommendation resulted from the same accident 
discussed under Safety Recommendation A-98-94, above. The airplane 
stalled before either the stall warning system or the stall 
protection system activated. As discussed in more detail later, this 
notice proposes to require applicants to demonstrate during type 
certification that their airplane provides adequate warning of an 
impending stall in icing conditions.
    Although we do not currently have a part 25 regulatory 
requirement for stall warning to be provided by a warning device in 
the cockpit, general industry design practice is to use a device 
called a stick shaker to shake the control column to warn the pilot 
of an impending stall.

XIV. Proposed Amendment

List of Subjects in 14 CFR Part 25:

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend part 25 of Title 14, Code of Federal 
Regulations, as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

    1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, and 44704

    2. Amend Sec.  25.21 by adding a new paragraph (g) to read as 
follows:


Sec.  25.21  Proof of compliance.

* * * * *
    (g) The requirements of this subpart associated with icing 
conditions apply only if certification for flight in icing conditions 
is desired. If certification for flight in icing conditions is desired, 
the following requirements also apply:
    (1) Each requirement of this subpart, except Sec. Sec.  25.121(a), 
25.123(c), 25.143(b)(1) and (b)(2), 25.149, 25.201(c)(2), 25.207(c) and 
(d), 25.239, and 25.251(b) through (e), must be met in icing 
conditions. Compliance must be shown using the ice accretions defined 
in appendix C, assuming normal operation of the airplane and its ice 
protection system in accordance with the operating limitations and 
operating procedures established by the applicant and provided in the 
Airplane Flight Manual.
    (2) No changes in the load distribution limits of Sec.  25.23, the 
weight limits of Sec.  25.25 (except where limited by performance 
requirements of this

[[Page 67298]]

subpart), and the center of gravity limits of Sec.  25.27, from those 
for non-icing conditions, are allowed for flight in icing conditions or 
with ice accretion.
    3. Amend Sec.  25.103 by revising paragraph (b)(3) to read as 
follows:


Sec.  25.103  Stall speed.

* * * * *
    (b) * * *
    (3) The airplane in other respects (such as flaps, landing gear, 
and ice accretions) in the condition existing in the test or 
performance standard in which VSR is being used;
* * * * *
    4. Amend Sec.  25.105 by revising paragraph (a) to read as follows:


Sec.  25.105  Takeoff.

    (a) The takeoff speeds prescribed by Sec.  25.107, the accelerate-
stop distance prescribed by Sec.  25.109, the takeoff path prescribed 
by Sec.  25.111, the takeoff distance and takeoff run prescribed by 
Sec.  25.113, and the net takeoff flight path prescribed by Sec.  
25.115, must be determined in the selected configuration for takeoff at 
each weight, altitude, and ambient temperature within the operational 
limits selected by the applicant--
    (1) In non-icing conditions; and
    (2) In icing conditions, if in the configuration of Sec.  25.121(b) 
with the takeoff ice accretion defined in appendix C:
    (i) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent 
of VSR; or
    (ii) The degradation of the gradient of climb determined in 
accordance with Sec.  25.121(b) is greater than one-half of the 
applicable actual-to-net takeoff flight path gradient reduction defined 
in Sec.  25.115(b).
* * * * *
    5. Amend Sec.  25.107 by revising paragraph (c)(3) and (g)(2) and 
adding new paragraph (h) to read as follows:


Sec.  25.107  Takeoff speeds.

* * * * *
    (c) * * *
    (3) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
* * * * *
    (g) * * *
    (2) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    (h) In determining the takeoff speeds V1, VR, 
and V2 for flight in icing conditions, the values of 
VMCG, VMC, and VMU determined for non-
icing conditions may be used.
    6. Amend Sec.  25.111 by revising paragraph (c)(3)(iii), (c)(4), 
and adding a new paragraph (c)(5) to read as follows:


Sec.  25.111  Takeoff path.

* * * * *
    (c) * * *
    (3) * * *
    (iii) 1.7 percent for four-engine airplanes.
    (4) The airplane configuration may not be changed, except for gear 
retraction and automatic propeller feathering, and no change in power 
or thrust that requires action by the pilot may be made until the 
airplane is 400 feet above the takeoff surface; and
    (5) If Sec.  25.105(a)(2) requires the takeoff path to be 
determined for flight in icing conditions, the airborne part of the 
takeoff must be based on the airplane drag:
    (i) With the takeoff ice accretion defined in appendix C, from a 
height of 35 feet above the takeoff surface up to the point where the 
airplane is 400 feet above the takeoff surface; and
    (ii) With the final takeoff ice accretion defined in appendix C, 
from the point where the airplane is 400 feet above the takeoff surface 
to the end of the takeoff path.
* * * * *
    7. Revise Sec.  25.119 to read as follows:


Sec.  25.119  Landing climb: All-engines-operating.

    In the landing configuration, the steady gradient of climb may not 
be less than 3.2 percent, with the engines at the power or thrust that 
is available 8 seconds after initiation of movement of the power or 
thrust controls from the minimum flight idle to the go-around power or 
thrust setting--
    (a) In non-icing conditions, with a climb speed of VREF 
determined in accordance with Sec.  25.125(b)(2)(i); and
    (b) In icing conditions with the landing ice accretion defined in 
appendix C, and with a climb speed of VREF determined in 
accordance with Sec.  25.125(b)(2)(ii).
    8. Amend Sec.  25.121 by revising paragraphs (b), (c), and (d) to 
read as follows:


Sec.  25.121  Climb: One-engine inoperative.

* * * * *
    (b) Takeoff; landing gear retracted. In the takeoff configuration 
existing at the point of the flight path at which the landing gear is 
fully retracted, and in the configuration used in Sec.  25.111 but 
without ground effect:
    (1) The steady gradient of climb may not be less than 2.4 percent 
for two-engine airplanes, 2.7 percent for three-engine airplanes, and 
3.0 percent for four-engine airplanes, at V2 with:
    (i) The critical engine inoperative, the remaining engines at the 
takeoff power or thrust available at the time the landing gear is fully 
retracted, determined under Sec.  25.111, unless there is a more 
critical power operating condition existing later along the flight path 
but before the point where the airplane reaches a height of 400 feet 
above the takeoff surface; and
    (ii) The weight equal to the weight existing when the airplane's 
landing gear is fully retracted, determined under Sec.  25.111.
    (2) The requirements of paragraph (b)(1) of this section must be 
met:
    (i) In non-icing conditions; and
    (ii) In icing conditions with the takeoff ice accretion defined in 
appendix C, if in the configuration of Sec.  25.121(b) with the takeoff 
ice accretion:
    (A) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent 
of VSR; or
    (B) The degradation of the gradient of climb determined in 
accordance with Sec.  25.121(b) is greater than one-half of the 
applicable actual-to-net takeoff flight path gradient reduction defined 
in Sec.  25.115(b).
    (c) Final takeoff. In the en route configuration at the end of the 
takeoff path determined in accordance with Sec.  25.111:
    (1) The steady gradient of climb may not be less than 1.2 percent 
for two-engine airplanes, 1.5 percent for three-engine airplanes, and 
1.7 percent for four-engine airplanes, at VFTO with--
    (i) The critical engine inoperative and the remaining engines at 
the available maximum continuous power or thrust; and
    (ii) The weight equal to the weight existing at the end of the 
takeoff path, determined under Sec.  25.111.
    (2) The requirements of paragraph (c)(1) of this section must be 
met:
    (i) In non-icing conditions; and
    (ii) In icing conditions with the final takeoff ice accretion 
defined in appendix C, if in the configuration of Sec.  25.121(b) with 
the takeoff ice accretion:
    (A) The stall speed at maximum takeoff weight exceeds that in non-
icing conditions by more than the greater of 3 knots CAS or 3 percent 
of VSR; or
    (B) The degradation of the gradient of climb determined in 
accordance with Sec.  25.121(b) is greater than one-half of the 
applicable actual-to-net takeoff flight path gradient reduction defined 
in Sec.  25.115(b).
    (d) Approach. In a configuration corresponding to the normal all-
engines-operating procedure in which VSR for

[[Page 67299]]

this configuration does not exceed 110 percent of the VSR 
for the related all-engines-operating landing configuration:
    (1) The steady gradient of climb may not be less than 2.1 percent 
for two-engine airplanes, 2.4 percent for three-engine airplanes, and 
2.7 percent for four-engine airplanes, with--
    (i) The critical engine inoperative, the remaining engines at the 
go-around power or thrust setting;
    (ii) The maximum landing weight;
    (iii) A climb speed established in connection with normal landing 
procedures, but not exceeding 1.4 VSR; and
    (iv) Landing gear retracted.
    (2) The requirements of paragraph (d)(1) of this section must be 
met:
    (i) In non-icing conditions; and
    (ii) In icing conditions with the holding ice accretion defined in 
appendix C. The climb speed selected for non-icing conditions may be 
used if the climb speed for icing conditions, computed in accordance 
with paragraph (d)(1)(iii) of this section, does not exceed that for 
non-icing conditions by more than the greater of 3 knots CAS or 3 
percent.
    9. Amend Sec.  25.123 by revising paragraphs (a) introductory text 
and (b) to read as follows:


Sec.  25.123  En route flight paths.

    (a) For the en route configuration, the flight paths prescribed in 
paragraph (b) and (c) of this section must be determined at each 
weight, altitude, and ambient temperature, within the operating limits 
established for the airplane. The variation of weight along the flight 
path, accounting for the progressive consumption of fuel and oil by the 
operating engines, may be included in the computation. The flight paths 
must be determined at a speed not less than VFTO, with--
* * * * *
    (b) The one-engine-inoperative net flight path data must represent 
the actual climb performance diminished by a gradient of climb of 1.1 
percent for two-engine airplanes, 1.4 percent for three-engine 
airplanes, and 1.6 percent for four-engine airplanes--
    (1) In non-icing conditions; and
    (2) In icing conditions with the en route ice accretion defined in 
appendix C, if:
    (i) A speed of 1.18 VSR with the en route ice accretion 
exceeds the en route speed selected for non-icing conditions by more 
than the greater of 3 knots CAS or 3 percent of VSR; or
    (ii) The degradation of the gradient of climb is greater than one-
half of the applicable actual-to-net flight path reduction defined in 
paragraph (b) of this section.
* * * * *
    10. Revise Sec.  25.125 to read as follows:


Sec.  25.125  Landing.

    (a) The horizontal distance necessary to land and to come to a 
complete stop (or to a speed of approximately 3 knots for water 
landings) from a point 50 feet above the landing surface must be 
determined (for standard temperatures, at each weight, altitude, and 
wind within the operational limits established by the applicant for the 
airplane):
    (1) In non-icing conditions; and
    (2) In icing conditions with the landing ice accretion defined in 
appendix C if VREF for icing conditions exceeds 
VREF for non-icing conditions by more than 5 knots CAS.
    (b) In determining the distance in (a):
    (1) The airplane must be in the landing configuration.
    (2) A stabilized approach, with a calibrated airspeed of not less 
than VREF, must be maintained down to the 50-foot height.
    (i) In non-icing conditions, VREF may not be less than:
    (A) 1.23 VSR0;
    (B) VMCL established under Sec.  25.149(f); and
    (C) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    (ii) In icing conditions, VREF may not be less than:
    (A) The speed determined in paragraph (b)(2)(i) of this section;
    (B) 1.23 VSR0 with the landing ice accretion defined in 
appendix C if that speed exceeds VREF for non-icing 
conditions by more than 5 knots CAS; and
    (C) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h) with the landing ice accretion defined in appendix C.
    (3) Changes in configuration, power or thrust, and speed, must be 
made in accordance with the established procedures for service 
operation.
    (4) The landing must be made without excessive vertical 
acceleration, tendency to bounce, nose over, ground loop, porpoise, or 
water loop.
    (5) The landings may not require exceptional piloting skill or 
alertness.
    (c) For landplanes and amphibians, the landing distance on land 
must be determined on a level, smooth, dry, hard-surfaced runway. In 
addition--
    (1) The pressures on the wheel braking systems may not exceed those 
specified by the brake manufacturer;
    (2) The brakes may not be used so as to cause excessive wear of 
brakes or tires; and
    (3) Means other than wheel brakes may be used if that means--
    (i) Is safe and reliable;
    (ii) Is used so that consistent results can be expected in service; 
and
    (iii) Is such that exceptional skill is not required to control the 
airplane.
    (d) For seaplanes and amphibians, the landing distance on water 
must be determined on smooth water.
    (e) For skiplanes, the landing distance on snow must be determined 
on smooth, dry, snow.
    (f) The landing distance data must include correction factors for 
not more than 50 percent of the nominal wind components along the 
landing path opposite to the direction of landing, and not less than 
150 percent of the nominal wind components along the landing path in 
the direction of landing.
    (g) If any device is used that depends on the operation of any 
engine, and if the landing distance would be noticeably increased when 
a landing is made with that engine inoperative, the landing distance 
must be determined with that engine inoperative unless the use of 
compensating means will result in a landing distance not more than that 
with each engine operating.
    11. Amend Sec.  25.143 by revising paragraphs (c), (d), (e), (f), 
and (g), and by adding new paragraphs (h), (i), and (j) to read as 
follows:


Sec.  25.143  General.

* * * * *
    (c) The airplane must be shown to be safely controllable and 
maneuverable with the critical ice accretion appropriate to the phase 
of flight defined in appendix C, and with the critical engine 
inoperative and its propeller (if applicable) in the minimum drag 
position:--
    (1) At the minimum V2 for takeoff;
    (2) During an approach and go-around; and
    (3) During an approach and landing.
    (d) The following table prescribes, for conventional wheel type 
controls, the maximum control forces permitted during the testing 
required by paragraph (a) through (c) of this section:

[[Page 67300]]



------------------------------------------------------------------------
 Force, in pounds, applied to the
  control wheel or rudder pedals      Pitch         Roll         Yaw
------------------------------------------------------------------------
For short term application for              75           50  ...........
 pitch and roll control--two
 hands available for control.....
For short term application for              50           25  ...........
 pitch and roll control--one hand
 available for control...........
For short term application for     ...........  ...........          150
 yaw control.....................
For long term application........           10            5           20
------------------------------------------------------------------------

    (e) Approved operating procedures or conventional operating 
practices must be followed when demonstrating compliance with the 
control force limitations for short term application that are 
prescribed in paragraph (d) of this section. The airplane must be in 
trim, or as near to being in trim as practical, in the preceding steady 
flight condition. For the takeoff condition, the airplane must be 
trimmed according to the approved operating procedures.
    (f) When demonstrating compliance with the control force 
limitations for long term application that are prescribed in paragraph 
(d) this section, the airplane must be in trim, or as near to being in 
trim as practical.
    (g) When maneuvering at a constant airspeed or Mach number (up 
VFC/MFC), the stick forces and the gradient of 
the stick versus maneuvering load factor must lie within satisfactory 
limits. The stick forces must not be so great as to make excessive 
demands on the pilot's strength when maneuvering the airplane, and must 
not be so low that the airplane can easily be overstressed 
inadvertently. Changes of gradient that occur with changes of load 
factor must not cause undue difficulty maintaining control of the 
airplane, and local gradients must not be so low as to result in a 
danger of overcontrolling.
    (h) The maneuvering capabilities in a constant speed coordinated 
turn at forward center of gravity, as specified in the following table, 
must be free of stall warning or other characteristics that might 
interfere with normal maneuvering:

----------------------------------------------------------------------------------------------------------------
                                                                        Maneuvering
                                                                      bank angle in a
             Configuration                          Speed               coordinated       Thrust/power setting
                                                                            turn
----------------------------------------------------------------------------------------------------------------
Takeoff................................  V2.........................         30[deg]   Asymmetric WAT-
                                                                                        limited.\1\
Takeoff................................  V2 + XX\2\.................         40[deg]   All-engines-operating
                                                                                        climb.\3\
En route...............................  VFTO.......................         40[deg]   Asymmetric WAT-
                                                                                        limited.\1\
Landing................................  VREF.......................         40[deg]   Symmetric for -3[deg]
                                                                                        flight path angle.
----------------------------------------------------------------------------------------------------------------
\1\ A combination of weight, altitude, and temperature (WAT) such that the thrust or power setting produces the
  minimum climb gradient specified in Sec.   25.121 for the flight condition.
\2\ Airspeed approved for all-engines-operating initial climb.
\3\ That thrust or power setting which, in the event of failure of the critical engine and without any crew
  action to adjust the thrust or power of the remaining engines, would result in the thrust or power specified
  for the takeoff condition at V2, or any lesser thrust or power setting that is used for all-engines-operating
  initial climb procedures.

    (i) When demonstrating compliance with Sec.  25.143 in icing 
conditions--
    (1) Controllability must be demonstrated with the ice accretion 
defined in appendix C that is most critical for the particular flight 
phase;
    (2) It must be shown that a push force is required throughout a 
pushover maneuver down to a zero g load factor, or the lowest load 
factor obtainable if limited by elevator power. It must be possible to 
promptly recover from the maneuver without exceeding 50 pounds pull 
control force; and
    (3) Any changes in force that the pilot must apply to the pitch 
control to maintain speed with increasing sideslip angle must be 
steadily increasing with no force reversals.
    (j) For flight in icing conditions before the ice protection system 
has been activated and is performing its intended function, the 
following requirements apply:
    (1) If activating the ice protection system depends on the pilot 
seeing a specified ice accretion on a reference surface (not just the 
first indication of icing), the requirements of Sec.  25.143 apply with 
the ice accretion defined in appendix C, part II(e).
    (2) For other means of activating the ice protection system, it 
must be demonstrated in flight with the ice accretion defined in 
appendix C, part II(e) that:
    (i) The airplane is controllable in a pull-up maneuver up to 1.5 g 
load factor; and
    (ii) There is no longitudinal control force reversal during a 
pushover maneuver down to 0.5 g load factor.
    12. Amend Sec.  25.207 by revising paragraph (b), revising 
paragraphs (e) and (f), and adding paragraphs (g) and (h) to read as 
follows:


Sec.  25.207  Stall warning.

* * * * *
    (b) The warning must be furnished either through the inherent 
aerodynamic qualities of the airplane or by a device that will give 
clearly distinguishable indications under expected conditions of 
flight. However, a visual stall warning device that requires the 
attention of the crew within the cockpit is not acceptable by itself. 
If a warning device is used, it must provide a warning in each of the 
airplane configurations prescribed in paragraph (a) of this section at 
the speed prescribed in paragraphs (c) and (d) of this section. Except 
for the stall warning prescribed in paragraph (h)(2)(ii) of this 
section, the stall warning for flight in icing conditions prescribed in 
paragraph (e) of this section must be provided by the same means as the 
stall warning for flight in non-icing conditions.
    (c) * * *
    (d) * * *
    (e) In icing conditions, the stall warning margin in straight and 
turning flight must be sufficient to allow the pilot to prevent 
stalling (as defined in Sec.  25.201(d)) when the pilot starts a 
recovery maneuver not less than three seconds after the onset of stall 
warning. When demonstrating compliance with this paragraph, the pilot 
must perform the recovery maneuver in the same way as for the airplane 
in non-icing conditions. Compliance with this requirement must be 
demonstrated in flight with the speed reduced at rates not exceeding 
one knot per second, with--
    (1) The en route ice accretion defined in appendix C for the en 
route configuration;

[[Page 67301]]

    (2) The holding ice accretion defined in appendix C for the holding 
and approach configurations;
    (3) The landing ice accretion defined in appendix C for the landing 
and go-around configurations; and
    (4) The more critical of the takeoff ice and final takeoff ice 
accretions defined in appendix C for each configuration used in the 
takeoff phase of flight.
    (f) The stall warning margin must be sufficient in both non-icing 
and icing conditions to allow the pilot to prevent stalling when the 
pilot starts a recovery maneuver not less than one second after the 
onset of stall warning in slow-down turns with at least 1.5 g load 
factor normal to the flight path and airspeed deceleration rates of at 
least 2 knots per second. When demonstrating compliance with this 
paragraph for icing conditions, the pilot must perform the recovery 
maneuver in the same way as for the airplane in non-icing conditions. 
Compliance with this requirement must be demonstrated in flight with--
    (1) The flaps and landing gear in any normal position;
    (2) The airplane trimmed for straight flight at a speed of 1.3 
VSR; and
    (3) The power or thrust necessary to maintain level flight at 1.3 
VSR.
    (g) Stall warning must also be provided in each abnormal 
configuration of the high lift devices that is likely to be used in 
flight following system failures (including all configurations covered 
by Airplane Flight Manual procedures).
    (h) For flight in icing conditions before the ice protection system 
has been activated and is performing its intended function, the 
following requirements apply, with the ice accretion defined in 
appendix C, part II(e):
    (1) If activating the ice protection system depends on the pilot 
seeing a specified ice accretion on a reference surface (not just the 
first indication of icing), the requirements of this section apply, 
except for paragraphs (c) and (d) of this section.
    (2) For other means of activating the ice protection system, the 
stall warning margin in straight and turning flight must be sufficient 
to allow the pilot to prevent stalling without encountering any adverse 
flight characteristics when the speed is reduced at rates not exceeding 
one knot per second and the pilot performs the recovery maneuver in the 
same way as for flight in non-icing conditions.
    (i) If stall warning is provided by the same means as for flight in 
non-icing conditions, the pilot may not start the recovery maneuver 
earlier than one second after the onset of stall warning.
    (ii) If stall warning is provided by a different means than for 
flight in non-icing conditions, the pilot may not start the recovery 
maneuver earlier than 3 seconds after the onset of stall warning. Also, 
compliance must be shown with Sec.  25.203 using the demonstration 
prescribed by Sec.  25.201, except that the deceleration rates of Sec.  
25.201(c)(2) need not be demonstrated.
    13. Amend Sec.  25.237 by revising paragraph (a) to read as 
follows:


Sec.  25.237  Wind velocities.

    (a) For landplanes and amphibians, the following applies:
    (1) A 90-degree cross component of wind velocity, demonstrated to 
be safe for takeoff and landing, must be established for dry runways 
and must be at least 20 knots or 0.2 VSRO, whichever is 
greater, except that it need not exceed 25 knots.
    (2) The crosswind component for takeoff established without ice 
accretions is valid in icing conditions.
    (3) The landing crosswind component must be established for:
    (i) Non-icing conditions, and
    (ii) Icing conditions with the landing ice accretion defined in 
appendix C.
* * * * *
    14. Amend Sec.  25.253 by revising paragraph (b), and adding a new 
paragraph (c) to read as follows:


Sec.  25.253  High-speed characteristics.

* * * * *
    (b) Maximum speed for stability characteristics. VFC/
MFC. VFC/MFC is the maximum speed at 
which the requirements of Sec. Sec.  25.143(g), 25.147(e), 
25.175(b)(1), 25.177, and 25.181 must be met with flaps and landing 
gear retracted. Except as noted in Sec.  25.253(c), VFC/
MFC may not be less than a speed midway between 
VMO/MMO and VDF/MDF, except 
that for altitudes where Mach number is the limiting factor, 
MFC need not exceed the Mach number at which effective speed 
warning occurs.
    (c) Maximum speed for stability characteristics in icing 
conditions. The maximum speed for stability characteristics with the 
ice accretions defined in appendix C, at which the requirements of 
Sec. Sec.  25.143(g), 25.147(e), 25.175(b)(1), 25.177, and 25.181 must 
be met, is the lower of:
    (1) 300 knots CAS;
    (2) VFC; or
    (3) A speed at which it is demonstrated that the airframe will be 
free of ice accretion due to the effects of increased dynamic pressure.
    15. Amend Sec.  25.773 by revising paragraph (b)(1)(ii) to read as 
follows:


Sec.  25.773  Pilot compartment view.

* * * * *
    (b) * * *
    (1) * * *
    (i) * * *
    (ii) The icing conditions specified in Sec.  25.1419 if 
certification for flight in icing conditions is requested.
* * * * *
    16. Amend Sec.  25.941 by revising paragraph (c) to read as 
follows:


Sec.  25.941  Inlet, engine, and exhaust compatibility.

* * * * *
    (c) In showing compliance with paragraph (b) of this section, the 
pilot strength required may not exceed the limits set forth in Sec.  
25.143(d), subject to the conditions set forth in paragraphs (e) and 
(f) of Sec.  25.143.
    17. Amend Sec.  25.1419 by revising the introductory text to read 
as follows:


Sec.  25.1419  Ice protection.

    If certification for flight in icing conditions is desired, the 
airplane must be able to safely operate in the continuous maximum and 
intermittent maximum icing conditions of appendix C. To establish 
this--
* * * * *
    18. Amend appendix C of part 25 by adding a new part I heading and 
a new paragraph (c) to part I; and adding a new part II to read as 
follows:

Appendix C of Part 25

Part I--Atmospheric Icing Conditions

    (a) * * *
    (c) Takeoff maximum icing. The maximum intensity of atmospheric 
icing conditions for takeoff (takeoff maximum icing) is defined by the 
cloud liquid water content of 0.35 g/m3, the mean effective 
diameter of the cloud droplets of 20 microns, and the ambient air 
temperature at ground level of minus 9 degrees Celsius (-9[deg]C). The 
takeoff maximum icing conditions extend from ground level to a height 
of 1,500 feet above the level of the takeoff surface.

Part II--Airframe Ice Accretions for Showing Compliance With Subpart B

    (a) Ice accretions--General. Section 25.21(g) states that if 
certification for flight in icing conditions is desired, the applicable 
requirements of subpart B must be met in the icing conditions of 
appendix C. The most critical ice accretion in terms of handling 
characteristics and performance for each flight phase must be 
determined, taking into consideration the atmospheric conditions of 
part I of this appendix, and the flight conditions (for example, 
configuration, speed, angle-of-attack,

[[Page 67302]]

and altitude). The following ice accretions must be determined:
    (1) Takeoff ice is the most critical ice accretion on unprotected 
surfaces, and any ice accretion on the protected surfaces appropriate 
to normal ice protection system operation, occurring between liftoff 
and 400 feet above the takeoff surface, assuming accretion starts at 
liftoff in the takeoff maximum icing conditions of part I, paragraph 
(c) of this appendix.
    (2) Final takeoff ice is the most critical ice accretion on 
unprotected surfaces, and any ice accretion on the protected surfaces 
appropriate to normal ice protection system operation, between 400 feet 
and 1,500 feet above the takeoff surface, assuming accretion starts at 
liftoff in the takeoff maximum icing conditions of part I, paragraph 
(c) of this appendix.
    (3) En route ice is the critical ice accretion on the unprotected 
surfaces, and any ice accretion on the protected surfaces appropriate 
to normal ice protection system operation, during the en route phase.
    (4) Holding ice is the critical ice accretion on the unprotected 
surfaces, and any ice accretion on the protected surfaces appropriate 
to normal ice protection system operation, during the holding flight 
phase.
    (5) Landing ice is the critical ice accretion on the unprotected 
surfaces, and any ice accretion on the protected surfaces appropriate 
to normal ice protection system operation following exit from the 
holding flight phase and transition to the final landing configuration.
    (6) Sandpaper ice is a thin, rough layer of ice.
    (b) In order to reduce the number of ice accretions to be 
considered when demonstrating compliance with the requirements of Sec.  
25.21(g), any of the ice accretions defined in paragraph (a) of this 
section may be used for any other flight phase if it is shown to be 
more conservative than the specific ice accretion defined for that 
flight phase.
    (c) The ice accretion that has the most adverse effect on handling 
characteristics may be used for airplane performance tests provided any 
difference in performance is conservatively taken into account.
    (d) Ice accretions for the takeoff phase. For both unprotected and 
protected parts, the ice accretion may be determined by calculation, 
assuming the takeoff maximum icing conditions defined in appendix C, 
and assuming that:
    (1) Airfoils, control surfaces and, if applicable, propellers are 
free from frost, snow, or ice at the start of the takeoff;
    (2) The ice accretion starts at liftoff;
    (3) The critical ratio of thrust/power-to-weight;
    (4) Failure of the critical engine occurs at VEF; and
    (5) Crew activation of the ice protection system is in accordance 
with a normal operating procedure provided in the Airplane Flight 
Manual, except that after beginning the takeoff roll, it must be 
assumed that the crew takes no action to activate the ice protection 
system until the airplane is at least 400 feet above the takeoff 
surface.
    (e) Ice accretion before the ice protection system has been 
activated and is performing its intended function. The ice accretion 
before the ice protection system has been activated and is performing 
its intended function is the ice accretion formed on the unprotected 
and normally protected surfaces before activation and effective 
operation of the ice protection system in continuous maximum 
atmospheric icing conditions.

    Issued in Washington, DC, on October 24, 2005.
John J. Hickey,
Director, Aircraft Certification Service.
[FR Doc. 05-21793 Filed 11-3-05; 8:45 am]
BILLING CODE 4910-13-P