[Federal Register Volume 61, Number 89 (Tuesday, May 7, 1996)]
[Rules and Regulations]
[Pages 20646-20667]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-10744]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 95-NM-146-AD; Amendment 39-9604; AD 96-09-28]
RIN 2120-AA64


Airworthiness Directives; Aerospatiale Model ATR-42 and ATR-72 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment supersedes an existing airworthiness directive 
(AD), applicable to all Aerospatiale Model ATR-42 and ATR-72 series 
airplanes. Unless modifications are accomplished or alternative 
procedures and training are adopted, that AD currently prohibits 
operation of the airplane in certain icing conditions, and requires 
restrictions on the use of the autopilot in certain conditions. That AD 
was prompted by an FAA determination that, during flight, in certain 
icing conditions, and with the airplane in a specific flight 
configuration, a ridge of ice can form on the wing and cause an 
interruption in the airflow over the ailerons, aileron deflection, and 
resultant lateral control forces. The actions specified by that AD are 
intended to prevent a roll upset from which the flight crew may be 
unable to recover. This action adds requirements for modification of 
the deicing boots on the leading edge of the wing and various follow-on 
actions. This action also removes certain limitations and procedures.

DATES: Effective June 11, 1996.
    The incorporation by reference of certain publications, as listed 
in the regulations, is approved by the Director of the Federal Register 
as of June 11, 1996.
    The incorporation by reference of Aerospatiale Service Bulletin 
ATR72-27-1039, dated January 12, 1995, listed in the regulations was 
approved previously by the Director of the Federal Register as of March 
8, 1995 (60 FR 9616, February 21, 1995).

ADDRESSES: The service information referenced in this AD may be 
obtained from Aerospatiale, 316 Route de Bayonne, 31060 Toulouse, Cedex 
03, France. This information may be examined at the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, Rules Docket, 
1601 Lind Avenue, SW., Renton, Washington; or at the Office of the 
Federal Register, 800 North Capitol Street, NW., suite 700, Washington, 
DC.

FOR FURTHER INFORMATION CONTACT: Gary Lium, Aerospace Engineer, 
Standardization Branch, ANM-113,

[[Page 20647]]

FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (206) 227-1112; fax (206) 227-1149.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) by superseding AD 95-02-51, 
amendment 39-9152 (60 FR 9616, February 21, 1995), which is applicable 
to all Aerospatiale Model ATR-42 and ATR-72 series airplanes, was 
published as a supplemental notice of proposed rulemaking (NPRM) in the 
Federal Register on January 25, 1996 (61 FR 2147). The action proposed 
to prohibit operation of the airplane in certain icing conditions 
unless modifications are accomplished or alternatives procedures and 
training are adopted, and to require restrictions on the use of the 
autopilot in certain conditions. The action also proposed to add 
requirements for modification of the deicing boots on the leading edge 
of the wing and various follow-on actions. In addition, the action 
proposed to remove certain limitations and procedures.

Disposition of Comments

    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    In addition to the proposed rule described previously, in January 
1996, the FAA issued 17 other similar proposals that address the 
subject unsafe condition on various airplane models (see below for a 
listing of all 18 proposed rules). These 17 proposals also were 
published in the Federal Register on January 25, 1996. This final rule 
contains the FAA's responses to all public comments received for each 
of these proposed rules.

----------------------------------------------------------------------------------------------------------------
           Docket No.                   Manufacturer/airplane model              Federal Register  citation     
----------------------------------------------------------------------------------------------------------------
96-CE-01-AD-                      de Havilland DHC-6 Series-.............  61 FR 2175                           
96-CE-02-AD-                      EMBRAER EMB-110P1/EMB-110P2-...........  61 FR 2183 -                         
96-CE-03-AD-                      Beech 99/200/1900 Series-..............  61 FR 2180                           
96-CE-04-AD-                      Dornier 228 Series-....................  61 FR 2172                           
96-CE-05-AD-                      Cessna 208/208B-.......................  61 FR 2178                           
96-CE-06-AD-                      Fairchild Aircraft SA226/SA227 Series..  61 FR 2189 -                         
96-CE-07-AD-                      Jetstream 3101/3201-...................  61 FR 2186                           
96-NM-13-AD-                      Jetstream BAe ATP-.....................  61 FR 2144                           
96-NM-14-AD-                      Jetstream 4101-........................  61 FR 2142                           
96-NM-15-AD-                      British Aerospace HS 748 Series........  61 FR 2139                           
96-NM-16-AD-                      Saab SF340A/SAAB 340B/SAAB 2000 Series.  61 FR 2169 -                         
96-NM-17-AD-                      CASA C-212/CN-235 Series-..............  61 FR 2166                           
96-NM-18-AD-                      Dornier 328-100 Series-................  61 FR 2157                           
96-NM-19-AD-                      EMBRAER EMB-120 Series-................  61 FR 2163                           
96-NM-20-AD-                      de Havilland DHC-7/DHC-8 Series........  61 FR 2154 -                         
96-NM-21-AD-                      Fokker F27 Mark 100/200/300/400/500/600/ 61 FR 2160 -                         
                                   700/050 Series-.                                                             
96-NM-22-AD-                      Short Brothers SD3-30/SD3-60/SD3-SHERPA  61 FR 2151 -                         
                                   Series.                                                                      
95-NM-146-AD-                     Aerospatiale ATR-42/ATR-72 Series......  61 FR 2147                           
----------------------------------------------------------------------------------------------------------------

-Comment 1. Support for the Proposals

    Numerous commenters support the FAA's intent to minimize the 
potential hazards associated with operating airplanes of any type 
design in severe icing conditions. One commenter states that the 
limitation prohibiting the use of flaps while enroute and during 
holding in icing conditions will be a positive contribution to safety. 
Additionally, several commenters support the requirement of the 
proposed AD for Aerospatiale airplanes for installation of modified 
deicing boots on the outer leading edges of the wings. One of these 
commenters states that the incorporation of AFM procedures, in addition 
to installation of the modified boots, provide a substantial margin of 
safety for the Aerospatiale fleet.

Comment 2. Requests Concerning References to ``Freezing Rain/Freezing 
Drizzle''

    Raytheon requests that references to a class of meteorological 
conditions in the limitations described as ``freezing rain or freezing 
drizzle'' should be removed from the proposed rules. Raytheon contends 
that instructions for the flight crew should be restricted to hazardous 
conditions that are defined by the accumulation of ice. The commenter 
states that the term ``severe icing'' has a specific meaning as defined 
in the Aeronautical Information Manual: ``The rate of accumulation is 
such that the icing/anti-icing equipment fails to reduce or control the 
hazard. Immediate diversion is necessary.'' The commenter states that, 
although freezing rain or freezing drizzle may involve drops larger 
than those specified in Appendix C of part 25 (``Airworthiness 
Standards: Transport Category Airplanes'') of the Federal Aviation 
Regulations (14 CFR part 25), flight into those conditions does not 
always result in accumulation of ice beyond the capability of the 
aircraft nor is severe icing always the result of freezing rain or 
freezing drizzle. Raytheon concludes that the limitation specified in 
paragraph (a)(1) of the proposals which reads, ``Flight in 
meteorological conditions described as freezing rain or freezing 
drizzle, as determined by the following visual cues, is prohibited,'' 
is an inference or conclusion that does not follow from the premises.
    The European Regional Airlines (ERA) Association states that the 
proposals define visual cues to be used to identify ``freezing rain'' 
and ``freezing drizzle,'' but these criteria are inconsistent with the 
criteria defined by the International Civil Aviation Organization 
(ICAO) and used by weather observers in aviation meteorological support 
services. The FAA infers from this remark that ERA requests the use of 
ICAO terminology associated with the visual cues.
    The FAA concurs partially. The FAA concurs that most of the 
references to ``freezing rain/freezing drizzle'' can be removed from 
the final rules. The FAA has revised the final rules to replace certain 
references to freezing rain and freezing drizzle with the words 
``severe icing.'' The FAA finds that since the visual cues contained in 
paragraph (a)(1) of these final rules indicate that icing conditions 
have exceeded the limits of the ice protection equipment, the use of 
the terminology ``severe icing'' is appropriate. As stated by one 
commenter, ``severe icing'' is terminology used to describe icing 
conditions that exceed the capabilities

[[Page 20648]]

of the ice protection equipment. The terminology ``severe icing'' is 
commonly used and understood within the aviation community. 
Additionally, there should be no confusion over the use of this term in 
the final rules because the AFM revisions required by these AD's define 
the terminology ``severe icing'' by specifying the visual cues that 
indicate when the capabilities of the ice protection equipment have 
been exceeded. However, the FAA would consider a request for approval 
of an alternative method of compliance to use terminology other than 
``severe icing'' in an AFM, in accordance with the provisions of these 
AD's, provided that adequate justification is presented to support such 
a request.
    Any inconsistencies that may exist between the criteria used by 
weather specialists to define ``severe icing'' and the criteria stated 
in these final rules are not relevant for these AD's because these AD's 
do not require the flight crew to take any action based on information 
provided by a weather observer. For these AD's, the flight crew must 
only take action if certain visual cues are present on the airplane.
    The FAA has determined that reference to freezing rain and freezing 
drizzle should not be removed from the text of the ``Caution'' that 
appears in paragraph (a)(2) of the proposals. [Note: The ``Caution'' 
appears as the ``Warning'' in paragraph (a)(1) of the final rules. An 
explanation of this change is contained in the disposition of Comment 
49 of these final rules.] Reference to freezing rain and freezing 
drizzle in that portion of text is made simply to provide a description 
of conditions that may result in ice build-up that exceeds the 
capabilities of the ice protection system.

Comment 3. Request for Review of ``Severe Icing'' Terminology

    One commenter, the Civil Aviation Authority (CAA), which is the 
airworthiness authority for the United Kingdom, requests that use of 
the terminology ``severe icing'' be reviewed. The CAA does not believe 
it is appropriate that this terminology becomes accepted for 
supercooled large droplet (SLD) conditions. The CAA indicates that a 
common interpretation for ``severe icing'' is that beyond the limit 
specified in Appendix C of part 25 of the Federal Aviation Regulations 
(14 CFR part 25), which is at or just over the capability of the ice 
protection system.
    The FAA has reviewed the use of the terminology ``severe icing'' as 
related to SLD. The FAA finds that ice resulting from SLD conditions 
may not always meet the criterion specified in the common 
interpretation of ``severe icing,'' as described by the commenter. The 
FAA notes that while SLD conditions may result in the formation of 
severe icing, severe icing also may accrue in conditions such as liquid 
water content, temperature, or extent of cloud, when those conditions 
exceed the limits specified in Appendix C of part 25 of the Federal 
Aviation Regulations (14 CFR part 25). As explained previously, most 
references to freezing rain and freezing drizzle have been replaced 
with the terminology ``severe icing.'' Additionally, the AFM's for the 
affected airplanes include a definition of severe icing.

Comment 4. Request To Withdraw the Proposals: Significant Economic 
Impact on Operating Community

    A number of commenters request that the proposals be withdrawn 
because the effect of these proposed AD's will produce a significant 
economic impact on the operating community. The commenters indicate 
that many flights would need to be canceled in order to make all 
reasonable efforts to avoid encounters with freezing rain/freezing 
drizzle conditions--i.e., when these conditions are forecast, airplanes 
will be prohibited from flight into those conditions. One commenter 
remarks that, based on the actual weather in January 1996, nearly 75 
percent of its scheduled flights would have been canceled due to 
forecast or actual freezing rain or freezing drizzle conditions if the 
AD's had been in effect. The commenters do not believe that the FAA has 
considered the economic factors affected by the proposed actions, such 
as the number of flights lost per day, crew costs, passenger 
compensation, misconnected baggage, etc.
    If the FAA does not withdraw the proposals, one commenter states 
that the prohibition of flight in freezing rain or freezing drizzle, as 
specified in paragraph (a)(1) of the proposals, should be revised. The 
commenter suggests the following: ``The aircraft should be immediately 
flown clear of icing conditions if ice is seen forming on the upper 
surface of the wing behind the leading edge deice boots.'' The 
commenter believes that the current wording in the proposals would 
cause flight crews to cancel or delay departure not only when freezing 
rain or freezing drizzle exists, but also when those conditions are 
forecast.
    The FAA concurs partially. The FAA finds that some misunderstanding 
exists among the commenters concerning the intent of these AD's. Many 
of the commenters believe that the AD's will prevent affected airplanes 
from flight in forecast freezing rain and freezing drizzle. This is not 
the case. The FAA agrees that certain language contained in the AD's 
must be clarified to reflect its intent. The FAA has evaluated the 
wording proposed by one of the commenters and agrees with it in 
principal. However, the FAA has determined that the first limitation in 
paragraph (a)(1) of the final rules must be revised in order to 
accommodate visual cues other than that specified by the commenter, to 
incorporate terminology familiar to the flight crew, and to emphasize 
that these AD's address only in-flight icing encounters. Additionally, 
in order to ensure that appropriate coordination with Air Traffic 
Control is accomplished, the FAA has revised the instruction following 
the visual cues in paragraph (a)(1), and has moved that instruction to 
the end of the first limitation in paragraph (a)(1) of the final rules. 
The entire limitation reads as follows: ``During flight, severe icing 
conditions that exceed those for which the airplane is certificated 
shall be determined by the following visual cues. If one or more of 
these visual cues exists, immediately request priority handling from 
Air Traffic Control to facilitate a route or an altitude change to exit 
the icing conditions.'' (Operators should note that, in the final rule 
for Aerospatiale airplanes, only one visual cue is specified. That cue 
involves ice on the side window of the airplane.)
    Several commenters question certain issues related to dispatch of 
the airplane in severe icing conditions. One commenter states that the 
procedures specified in the proposed AD's fail to address the 
conditions that would prohibit takeoff in freezing rain and freezing 
drizzle. The commenter believes the visual cues provided in the 
proposals would only appear on an airplane during flight. Thus, 
allowable conditions for takeoff during times of forecast freezing rain 
or freezing drizzle are left to the individual operator's 
interpretation. Another commenter believes that the FAA has not 
established a basis for prohibiting flight in all reported freezing 
drizzle. The commenter contends that takeoff in freezing rain should 
always be prevented, but takeoff in freezing drizzle should be possible 
after applying appropriate deicing or anti-icing treatments. One 
commenter requests that the FAA clarify how the procedures for exiting 
freezing rain/freezing drizzle conditions would apply to takeoff and 
landing. The commenter states that landing during those conditions 
might,

[[Page 20649]]

in many cases, be the most expeditious method of avoiding a hazardous 
condition. Another commenter suggests that the AFM for Aerospatiale 
airplanes should be revised to reflect standard dispatch rules; 
however, the commenter provides no justification for this request.
    The FAA concurs that visual cues that would prohibit takeoff in 
freezing rain or freezing drizzle were not provided because the FAA's 
intent is that these AD's address only in-flight icing encounters. 
These AD's do not affect any existing regulations or FAA-approved 
operating procedures related to takeoff, dispatch, or release of an 
airplane in icing conditions. These AD's only prohibit remaining in 
icing conditions when certain visual cues are present on the airplane; 
these AD's do not prohibit flight into forecast or reported freezing 
drizzle. Operators must comply with existing rules that require an 
airplane to be free of ice prior to takeoff. Further, the FAA finds no 
need to revise the AFM for Aerospatiale airplanes to reflect standard 
dispatch rules. The FAA also considers that landing the airplane when 
freezing rain/freezing drizzle conditions are encountered would, in 
many cases, be the most expeditious method of exiting the conditions. 
Such landing would be in compliance with the limitation that requires 
the flight crew to exit the severe icing conditions.
    Two commenters indicate that the first note that appears in 
paragraph (a)(1) of the proposed rules could be interpreted to mean 
that if freezing rain or freezing drizzle is forecast anywhere along 
the route of flight, the airplane could not be dispatched. One of the 
commenters concludes that forecasting methodologies are inadequate and 
would need to be improved. The other commenter suggests that the FAA 
remove the word ``purely'' from the note. The same commenter requests 
that the FAA clarify that the airplane may be dispatched if the 
forecast may indicate freezing rain/freezing drizzle conditions. 
Another commenter indicates that the wording of the same note is 
unclear as to how the FAA defines a ``purely'' inadvertent encounter. 
The commenter states that examples of such purely inadvertent 
encounters would be helpful.
    One commenter asks the following questions in regard to the same 
note:

--What are ``reasonable efforts?''
--What does ``immediately exit'' mean? Are the procedures for 
immediately exiting listed in the Air Traffic Controller's Handbook or 
the Airman's Information Manual? Can a pilot operating the airplane in 
a holding pattern decide on his/her own to immediately descend below 
the freezing level without regard to other traffic?

    One commenter states that the note should be placed in the Normal 
Procedures Section of the AFM, rather than in the Limitations Section. 
The commenter provides no justification for this request.
    The FAA concurs that clarification of this note is necessary. The 
FAA originally included the note in the AD's to clarify the intent of 
the rules. Since the first instruction and the limitation that follows 
have been revised in these final rules, the FAA finds that inclusion of 
the clarifying note is no longer necessary. In order to avoid any 
possible misinterpretation of the intent of the limitation on flight in 
freezing rain or freezing drizzle, the FAA has removed the first note 
that appeared in paragraph (a)(1) of the proposals. These AD's do not 
prohibit flight into forecast or reported freezing rain or freezing 
drizzle. This means that the aircraft is not prohibited from takeoff, 
dispatch, or release simply because the forecast may indicate freezing 
rain or freezing drizzle, but is prohibited from continued flight in 
severe icing conditions.

Comment 5. Request To Withdraw the Proposals: No Unsafe Condition Has 
Been Established

    Several commenters request that the proposals be withdrawn because 
no unsafe condition has been established with respect to airplane 
handling characteristics in severe icing conditions. One commenter 
states that the preamble of the proposals does not provide data that 
establish an unsafe condition; the preamble only indicates that there 
are inadequate data to represent all possible conditions. Another 
commenter remarks that the FAA's dismissal of the significance of the 
test results with the specious comment, ``such airplanes could develop 
ice shapes other than those tested,'' is wholly speculative, and is an 
invalid basis on which to issue an AD under the provisions of part 39 
(``Airworthiness Directives'') of the Federal Aviation Regulations (14 
CFR part 39).
    The FAA does not concur that these AD's should be withdrawn. As 
stated in the preamble to the proposals, the FAA has not required that 
airplanes be shown to be capable of operating safely in icing 
conditions outside the icing certification envelope specified in 
Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part 
25). This means that any time an airplane is flown in icing conditions 
for which it is not certificated, there is a potential for an unsafe 
condition to exist or develop and the flight crew must take steps to 
exit those conditions expeditiously. Further, the FAA has determined 
that flight crews are not currently provided with adequate information 
necessary to determine when an airplane is operating in icing 
conditions for which it is not certificated or what action to take when 
such conditions are encountered. The absence of this information 
presents an unsafe condition because without that information, a pilot 
may remain in icing conditions for which the airplane has not been 
proven to be safe. These AD's correct the unsafe condition by requiring 
AFM revisions that provide the flight crews with visual cues to 
determine when icing conditions have been encountered for which the 
airplane is not certificated, and by providing procedures to safely 
exit those conditions.
    Additionally, in the preamble to the proposed rules, the FAA 
discussed the investigation of roll control anomalies to explain that 
this investigation was not a complete certification program. The 
testing was designed to examine only the roll handling characteristics 
of the airplane in certain droplets the size of freezing drizzle. The 
testing was not a certification test to approve the airplane for flight 
into freezing drizzle. The results of the tests were not used to 
determine if these final rules were required, but rather to determine 
if design changes were needed to prevent a catastrophic roll upset. The 
roll control testing and the AD's must be viewed as two unrelated 
actions.

Comment 6. Request To Withdraw the Proposals: Unsafe Condition is 
Outside Certification Limits

    One commenter states that the proposed AD's should be withdrawn 
because the issuance of AD's to address the problems of icing 
encounters outside of the limits for which the airplane is certificated 
is a completely inappropriate application of part 39 of the Federal 
Aviation Regulations (14 CFR part 39). Another commenter contends that 
since the Aerospatiale aircraft passed all present certification 
testing, what transpired beyond the limits of certification should not 
be held against that aircraft.
    The FAA does not concur that the AD's should be withdrawn on the 
basis that the unsafe condition is outside the icing certification 
envelope. Flight in icing conditions that are outside the icing 
certification envelope occurs during the normal service life of an 
airplane. Apart from the visual cues provided in these final rules, 
there is no

[[Page 20650]]

existing method provided to the flight crews to identify when the 
airplane is in a condition that exceeds the icing certification 
envelope. The appropriate vehicle for providing this method of 
identification is through issuance of an AD. The FAA acknowledges that 
the Aerospatiale airplane has been shown to comply with existing 
certification rules; however, no airplane is certificated for flight in 
icing conditions outside of Appendix C of part 25 of the Federal 
Aviation Regulations (14 CFR part 25).

Comment 7. Request To Withdraw the Proposals: Proposals Unfairly 
Discriminate Against Turbopropeller-Powered Aircraft

    Several commenters state that the proposed AD's should be withdrawn 
because the AD's unfairly discriminate against turbopropeller-powered 
aircraft. The commenters contend that by issuing these proposed rules, 
the FAA is creating a public perception that turbopropeller-powered 
aircraft are less safe than other aircraft.
    Numerous commenters oppose the statement contained in the preamble 
of the proposals which indicates that since turbopropeller-powered 
airplanes are more likely to operate at low altitudes and to make more 
frequent landings, they are more likely to encounter icing conditions 
that are outside the icing envelope. One commenter states that the mere 
fact that turbopropeller-powered airplanes make more frequent landings 
is irrelevant for the following reasons:

--Every flight encounters the same atmospheric conditions after takeoff 
and prior to landing, whether the airplane is powered by a 
turbopropeller or turbojet engine;
--There are numerous airplanes powered by turbojet engines that operate 
on segments equal in duration to those operated by many turbopropeller-
powered aircraft; numerous airplanes powered by turbojet engines make 
just as frequent landings; and
--Even if turbopropeller-powered aircraft do make more frequent 
landings, there is no negative inference to be drawn from that fact; 
more opportunities are available to ensure that ice has not formed on 
the aircraft if the aircraft lands more frequently.

    One commenter states that the altitudes where SLD conditions exist 
are the same altitudes at which jets would encounter those conditions 
during the departure and arrival phases of flight. Flight in SLD 
conditions that would have a negative effect on a turbopropeller-
powered airplane would have the same effect on a jet, since both are 
certificated under the same rules with regard to flight into adverse 
weather, and both fly at about the same speeds during the departure and 
arrival phases of flight. Additionally, another commenter adds that no 
airplane, whether it is powered by a turbopropeller, turbojet, or 
turbofan engine, is certificated for operation in SLD conditions.
    Another commenter indicates that icing encounters take place at 
altitudes below the cruising altitudes of most turbopropeller-powered 
aircraft used in scheduled service; this also occurs on airplanes 
powered by turbojet engines. Icing encounters occur during takeoff, 
climb, descent, holding, and landing phases of flight on both types of 
aircraft. The commenter adds that operating the airplane in a holding 
pattern for a prolonged period in severe icing conditions is hazardous 
for both turbojet and turbopropeller-powered aircraft. The commenter 
explains that, although the exposure time per flight hour of a long-
haul jet aircraft is less, the exposure on a per flight basis is 
exactly the same. The commenter states that, like landing gear life 
limits, the proper measure of exposure to freezing rain/freezing 
drizzle should be the number of flights, not the number of flight 
hours.
    Another commenter, Saab, states that Saab Model SAAB 2000 series 
airplanes have a unique power-to-weight ratio, which makes it 
comparable with airplanes of the same size and, in some relevant areas 
such as climb performance and single engine ceiling, even far superior. 
Operators of those airplanes can operate the aircraft over-the-weather 
at flight level (FL) 310. This means that these Saab airplanes operate 
on jet profiles and, therefore, are not exposed to the icing conditions 
that are outside the icing envelope any more than the airplanes that 
are excluded from the proposals.
    The FAA does not concur that the proposals should be withdrawn. The 
FAA does not intend to imply through issuance of these AD's that 
turbopropeller-powered airplanes are less safe than airplanes having 
other types of propulsion systems. As stated in the preamble of the 
proposals, the FAA addressed certain airplanes as a higher priority for 
two reasons:

--Turbopropeller-powered airplanes are more likely to operate at low 
altitudes and to make more frequent landings; therefore, they are more 
likely to encounter icing conditions that are outside the icing 
envelope specified in Appendix C of part 25 of the Federal Aviation 
Regulations (14 CFR part 25); and
--The flight crew of an airplane having an unpowered roll control 
system must rely solely on physical strength to counteract roll control 
anomalies, whereas a roll control anomaly that occurs on an airplane 
having a powered roll control system need not be offset directly by the 
flight crew.

    Since the issuance of the proposed rules, the FAA has reconsidered 
this reasoning. The FAA acknowledges that simply because an airplane is 
turbopropeller-powered and has a particular flight profile, that 
airplane should not be addressed as a higher priority. However, this 
does not diminish the significance of the necessity of the flight crew 
of an airplane having an unpowered roll control system to rely on 
physical strength to counteract roll control anomalies. The subject 
airplanes all have pneumatic deicing boots and unpowered aileron 
controls, which have been common denominators in the accident and 
incident history concerning flight in icing conditions and, in 
particular, during conditions when SLD was believed to be present. 
Therefore, airplanes having those design features are of immediate 
concern to the FAA and were addressed as a higher priority. 
Additionally, these AD's primarily address airplanes used in regularly 
scheduled passenger service in the United States.
    The FAA finds that the comment indicating that more frequent 
landings provides more opportunity to verify that ice has not formed is 
irrelevant. It also could be said that more frequent landings gives 
more opportunity for ice to form. The FAA agrees with the statement 
that holding for prolonged periods in severe icing conditions is 
hazardous for all aircraft types. The FAA is considering initiating an 
assessment of the need to prohibit all aircraft from continued flight 
in severe icing conditions as defined in these AD's.
    Although Transport Canada Aviation does not request that the 
proposed AD's be withdrawn, the commenter indicates that roll control 
anomalies could exist for all aircraft whether they have powered or 
unpowered roll control systems. Transport Canada Aviation adds that 
some jet-powered aircraft have unpowered ailerons.
    The FAA concurs that roll anomalies could exist for all aircraft 
whether they have powered or unpowered roll control systems. However, 
these AD's address airplanes having both deicing boots and unpowered 
aileron controls. The FAA

[[Page 20651]]

acknowledges that other airplanes that have powered ailerons may be 
subject to roll problems in severe icing conditions due to loss of 
lift. However, the FAA is not aware of a mechanism that would allow ice 
to produce an uncommanded control deflection on airplanes having 
powered flight control systems. In addition, airplanes having powered 
roll control systems do not have direct feedback of aerodynamic forces 
to the pilot. However, the FAA is considering initiating an assessment 
of the need to apply similar limitations to other aircraft types.

Comment 8. Request To Withdraw the Proposals: Affected Airplanes Are 
Not Same Type Design as Accident Airplane

    Several commenters contend that the proposals should be withdrawn 
because the FAA has not established clearly that the airplanes 
addressed in the proposed rules have the same type design as the 
Aerospatiale Model ATR-72 series airplane that was involved in an 
accident in October 1994 that occurred in severe icing conditions.
    One commenter questions the words ``same type design,'' and asks if 
those words refer to high wing, low wing, T-tail, or aircraft of 
another type design.
    Three commenters provide justification in support of a request that 
certain airplanes be exempt from these AD's:
     de Havilland Model DHC-7 and DHC-8 series airplanes: De 
Havilland states that the airplanes it manufactures share a 
conservative aerodynamic design philosophy that yields exceptional low-
speed handling qualities and demonstrated benign handling qualities in 
icing conditions. De Havilland adds that two-thirds of the roll control 
authority of these airplanes is provided by hydraulically powered roll 
spoilers. A second commenter adds that increased testing has been 
conducted on these airplanes.
     Fokker F27 Mark 100, 200, 300, 400, 500, 600, 700, and 050 
series airplanes: Fokker states that the leading edge boots on Fokker 
Model F27 series airplanes and Model F27 Mark 050 series airplanes 
extend to a chord wise position, 12.5 percent wing chord, which 
precludes all but the very largest droplets impinging on the 
unprotected surfaces. Fokker adds that since the accident airplane has 
unshielded horn balances and the affected Fokker airplanes do not have 
these unshielded horn balances, Fokker airplanes will not experience 
roll upset problems. Fokker indicates that aerodynamically balancing 
the control surfaces by means of unshielded horn balances was not 
applied because of the bad service experience of the Vickers Viking 
aircraft in 1946.
     Beech Model 200 and 200C airplanes: Raytheon states that 
these particular airplane models are not normally considered to be 
commuter aircraft, and that issuance of an AD would be contrary to the 
stated purpose of the proposals because most of these airplanes are 
used in non-revenue service. Raytheon states that these airplanes are 
all low wing aircraft. Aerospatiale Model ATR-72 series airplanes (the 
accident airplane) is 50 percent larger and carries over twice the 
number of passengers as these Beech aircraft. For these reasons, as 
well as other differences in the geometry of the airplanes (i.e., 
relative aileron span), Raytheon states that the supposition of an 
icing hazard in these aircraft is purely speculative.
    The FAA does not concur that any of the addressed airplanes should 
be exempt from these AD's. The FAA has examined the accident and 
incident history in icing conditions and, in particular, those events 
believed to involve SLD conditions. Results of this examination 
revealed that the type design characteristics that appear to be common 
in these events are pneumatic deicing boots and unpowered aileron 
controls. Airplanes having those type design characteristics appear to 
be more susceptible to control problems in severe icing conditions. In 
response to Fokker's remark that its airplanes will not experience roll 
control problems since those airplanes do not have unshielded horn 
balances, the FAA has determined that horn balances on the accident 
airplane were not the source of the uncommanded aileron motion. Design 
similarities of the wing, tail, or ailerons do not appear to be a 
common denominator among airplanes involved in accidents or incidents 
where SLD conditions may have been present.
    Saab asks for removal of the sentence that reads, ``Since an unsafe 
condition has been identified that is likely to exist or develop on 
other airplanes of the same type design . * * *'' Saab states that this 
sentence implies that Saab Model SF340A and SAAB 340B series airplanes 
have a problem and that this problem is ``likely to develop on other 
airplanes of the same type design.'' Yet, there have been no reported 
problems on those airplanes, which are not of the same type design as 
all other turbopropeller-powered airplanes. Transport Canada Aviation 
does not request that the proposals be withdrawn; however, the 
commenter requests that the FAA revise the same phrase discussed by 
Saab. Transport Canada Aviation requests that the phrase be reworded as 
follows: ``Since an unsafe condition has been identified where aircraft 
icing certification is not adequate to address the conditions that are 
outside of Appendix C of FAR part 25 . . . .''
    The FAA does not concur with Saab's request. The FAA acknowledges 
that there have been no reported problems involving severe icing 
conditions on Saab airplanes. However, Saab Model SF340A and SAAB 340B 
series airplanes have pneumatic deicing boots and unpowered aileron 
controls, which have been determined to be the common denominators 
among the airplanes involved in accidents and incidents in severe icing 
conditions. Therefore, the FAA has determined that when severe icing 
conditions are encountered on these Saab airplanes, those conditions 
must be exited.
    Although the FAA has no technical objection to the revised wording 
proposed by Transport Canada Aviation, this sentence does not reappear 
in the final rules. Therefore, no change to the final rule is 
necessary.

Comment 9. Request for Explanation of the Applicability of the AD's

    One commenter requests an explanation of the methodology used by 
the FAA to determine that AD's should not be issued for Cessna and 
Piper multi-engine aircraft. The commenter also asks if an AD similar 
to the proposed rules exists for Boeing Model 737 series airplanes. The 
commenter indicates that Model 737 series airplanes have demonstrated 
abnormal and unexplained roll tendencies.
    The FAA provides the following clarification for this commenter. No 
AD's have been issued for Piper airplanes or Boeing Model 737 series 
airplanes. However, as reflected in the table above, the FAA has issued 
an AD for Cessna Model 208 and 208B airplanes.
    Most of the aircraft affected by these final rules are used 
primarily in regularly scheduled passenger service in the United 
States. However, there are some airplanes affected by the final rules 
that are not used in regularly scheduled passenger service. Two of 
these are Cessna Model 208 and 208B airplanes. Those airplanes were 
included in the final rules because of their accident and incident 
history in icing conditions. The FAA is considering an assessment of 
the need to prohibit all aircraft from continued flight in severe icing 
conditions.

[[Page 20652]]

Comment 10. Request To Withdraw the Proposals: Service Experience of 
Affected Airplanes is Satisfactory

    Several commenters indicate that the FAA should withdraw the 
proposed AD's in light of the satisfactory service experience of the 
airplanes addressed in the proposals. The commenters believe that the 
FAA is singling out turbopropeller-powered aircraft without any regard 
for the operational record of those aircraft.
    Several commenters provide justification in support of this 
request:
     One commenter states that de Havilland airplanes have been 
successfully operated for over 30 years without one instance of roll 
upset or flight control problems.
     De Havilland indicates that de Havilland Model DHC-8 
series airplanes have been in service for 11 years and have accumulated 
6 million flights and 5 million flight hours without any incidents due 
to icing.
     De Havilland adds that de Havilland Model DHC-7 series 
airplanes have been in service for 18 years and have accumulated 3.7 
million flights and 2.7 million flight hours without any incidents due 
to icing.
     Another commenter has not experienced any icing related 
upsets or control irregularities in its fleet of de Havilland Model 
DHC-8 series airplanes and Beech Model 1900 series airplanes.
     One commenter operates 21 Beech Model 1900D airplanes, 32 
EMBRAER Model EMB-120 series airplanes, and 41 Aerospatiale Model ATR-
42 and ATR-72 series airplanes; none of these airplanes have 
experienced any icing incidents this season.
     One commenter indicates that airplanes produced by Beech, 
EMBRAER, and Jetstream Aircraft Limited (JAL) have no record of 
uncommanded roll due to asymmetrical build-up of ice on surfaces beyond 
the deicing boots.
     One commenter notes that it has not experienced any 
unusual icing characteristics on its fleet of EMBRAER Model EMB-120 
series airplanes and Aerospatiale Model ATR-72 series airplanes.
     Fairchild notes that in over 26 years and 15,000,000 
flight hours in passenger service, there has never been a reported 
incident where the controllability of Fairchild Aircraft SA226 and 
SA227 series airplanes were in jeopardy as a result of any icing 
encounters (including SLD icing encounters).
     The Luftfartsverket (LFV), which is the airworthiness 
authority for Sweden, states that no ice build-up behind the wing boots 
has ever been reported on Saab Model SF340A, SAAB 340B, or SAAB 2000 
series airplanes. Additionally, the leading edge on these airplanes can 
be inspected easily during flight.
     Saab remarks that no roll anomaly problems in icing 
conditions have occurred during the extensive service experience of 
Saab Model SF340A and SAAB 340B series airplanes.
     The FAA does not concur that the AD's should be withdrawn. 
The fact that an airplane has a perfect safety record in icing does not 
negate the fact that no airplane has been certificated for flight into 
SLD. The FAA has determined that a need exists to provide the flight 
crew with useful safety-related information regarding the limitations 
of the airplane concerning flight in severe icing conditions. The 
purpose of issuing these final rules is to provide the flight crew with 
such information.
    One commenter, Transport Canada Aviation, requests that the 
proposals apply only to those airplanes that have a demonstrated 
history of in-service problems as a priority. The commenter states that 
the hazards relating to operation in icing conditions exist for all 
types of aircraft. (The commenter does not request that the proposed 
rules be withdrawn.)
    The FAA does not concur with this request. As explained previously, 
the FAA has issued AD's for airplanes having pneumatic deicing boots 
and unpowered aileron controls as a priority. Airplanes having these 
design features are of immediate concern to the FAA because these 
features have been common denominators in the accident and incident 
history concerning flight in icing conditions and, in particular, 
during conditions when SLD was believed to be present. The FAA is 
considering the need for rulemaking to impose similar limitations on 
other aircraft.

Comment 11. Request To Withdraw the Proposals: Extensive Testing 
Revealed No Icing Problems

    Several commenters request that the proposals be withdrawn because 
extensive testing revealed no icing problems on many different 
turbopropeller-powered airplanes, even though those tests likely 
exceeded any icing certification tests ever performed on other civil 
aircraft types, including large jet-powered transport category 
airplanes. Fokker states that Fokker Model F27 series airplanes do not 
demonstrate unacceptable roll control characteristics in severe icing 
conditions; however, Fokker submits no data to substantiate this 
statement.
    The FAA does not concur. The FAA finds that successful completion 
of the roll upset evaluation is not a valid reason for withdrawing the 
AD's. On the contrary, if the evaluation had demonstrated anomalies, 
the FAA may have concluded that action beyond that required by these 
AD's was necessary to address the demonstrated unsafe condition. The 
testing was designed to examine only the roll handling characteristics 
of the airplane in certain droplets the size of freezing drizzle to 
determine if any design changes are necessary to prevent catastrophic 
control surface deflection. The testing was not a certification test to 
approve the airplane for flight into freezing drizzle since many of the 
components and their functions were not tested (e.g., pitch control, 
engine and propeller, performance, stall warning, windshield, air data 
sensors and fuel system vents). Further, freezing rain was not tested. 
Satisfactory demonstration of those tests does not remove the FAA's 
responsibility to provide a safe operating environment for the 
passengers and crew.
    JAL comments that its airplanes are not subject to the addressed 
unsafe condition, and that the FAA had concurred with this contention. 
JAL states that the FAA agreed that, by the controllability evaluation 
process, all Jetstream aircraft types had been demonstrated to be not 
susceptible to roll control anomalies in freezing rain or freezing 
drizzle conditions.
    The FAA does not concur with JAL's position concerning its 
airplanes. All Jetstream airplanes affected by these AD's successfully 
completed the roll upset evaluation. However, as stated previously, no 
airplanes were tested in freezing rain conditions. The roll upset 
evaluation only addressed conditions that were believed to have existed 
during an accident involving a transport category airplane that 
occurred in October 1994. Therefore, since no airplane has been tested 
in all freezing rain and freezing drizzle conditions, no airplane has 
been demonstrated to be safe for continued flight in these conditions.

Comment 12. Request To Withdraw the Proposals: Publish Advisory 
Materials and Require Training

    Several commenters request that, in lieu of issuing the proposed 
rules, the FAA publish appropriate advisory materials and require 
training for recognition, avoidance, and exit from severe icing 
encounters as part of the required severe weather training for pilots 
and dispatchers. Two commenters suggest that the FAA include such

[[Page 20653]]

requirements in the operating rules specified in part 121 
(``Certification and Operations: Domestic, Flag, and Supplemental Air 
Carriers and Commercial Operators of Large Aircraft'') of the Federal 
Aviation Regulations (14 CFR part 121). Another commenter indicates 
that, since jets and piston-engine aircraft also could develop ice 
shapes other than those tested, training should not be provided only to 
pilots of turbopropeller-powered airplanes, but to pilots of all 
aircraft. Some commenters also suggest that the FAA has successfully 
addressed other issues through increased awareness and training 
requirements, rather than by issuing AD's against every airplane type 
design to require revising the Limitations Section of the AFM. The 
commenters cite windshear, ground deicing, and clear air turbulence as 
examples of such issues. The commenters contend that, except where 
configuration changes are needed, such as in the case of windshear 
detection devices, improved awareness and training programs--not AD's--
have been highly effective in achieving needed safety improvements.
    The FAA does not concur. The FAA considers that substituting 
advisory material and mandatory training for issuance of an AD is not 
appropriate, nor would this adequately address the unsafe condition. 
The FAA fully supports the development of advisory materials and 
training. Part 121 (``Certification and Operations: Domestic, Flag, and 
Supplemental Air Carriers and Commercial Operators of Large Aircraft'') 
and part 135 (``Air Taxi Operators and Commercial Operators'') of the 
Federal Aviation Regulations (14 CFR parts 121 and 135) require that 
appropriate training concerning limitations such as those contained in 
these AD's be incorporated into air carriers' training programs. 
However, the FAA's position is that the development and use of such 
advisory materials and training alone are not adequate to address the 
subject unsafe condition. Currently, the AFM's specify that the 
affected airplanes are certificated for flight in icing conditions; 
however, the AFM's do not specify a method of determining whether the 
certification limits for those conditions have been exceeded. 
Consequently, the FAA finds that these AFM's must be revised to provide 
limitations for flight in icing conditions and to provide the flight 
crew with a method of determining when those limitations have been 
exceeded.
    The FAA does not concur that amending part 121 of the Federal 
Aviation Regulations (14 CFR part 121) in lieu of issuing these AD's is 
appropriate. The FAA's position is that the appropriate place to inform 
the flight crew of the limitations of the airplane is in the AFM. The 
appropriate vehicle for mandating such AFM revisions is through 
issuance of an AD. In addition, an AD will ensure that the 
incorporation of such AFM revisions is not left to each operator's 
individual discretion and that flight crews receive pertinent 
information. The FAA may consider an assessment of the need to provide 
training to pilots of all aircraft types for flight in severe icing 
conditions.
    The commenters reference windshear as an example of an issue that 
was handled successfully without issuance of an AD to revise the AFM's. 
In this case, the AFM's for all airplanes having an onboard windshear 
system were revised to provide the flight crew with procedures for 
responding when the system gives an alert. Although no AD was issued to 
mandate these AFM revisions, without revising the AFM, operators could 
not comply with the section of part 121 of the Federal Aviation 
Regulations (14 CFR part 121) that requires installation of the 
windshear detection devices. In conclusion, although AFM revisions were 
not required by an AD, AFM changes were mandated indirectly by a new 
part 121 regulation.
    The commenters also reference ground deicing. Part 91 (``General 
Operating and Flight Rules'') of the Federal Aviation Regulations (14 
CFR part 91) prohibits takeoff of an airplane unless the airframe is 
clear of ice; therefore, there is no need to provide additional 
limitations concerning the amount of ice that would be acceptable for 
takeoff. However, in the case of severe icing conditions addressed by 
these final rules, the AFM's currently allow flight in icing, but the 
AFM does not define when the limits of the certificated icing operation 
envelope have been exceeded.
    Concerning the issue of clear air turbulence, issuance of an AD was 
not required because an airspeed limitation associated with turbulent 
air penetration was already in the AFM's. Therefore, in this case, the 
issue was addressed in the AFM as well as through awareness and 
training.

Comment 13. Request To Withdraw the Proposals: Incorporate Operational 
Issues into a Training Curriculum

    Two commenters request that the proposals be withdrawn because the 
proposed AD's address an operational issue that should be incorporated 
into an operator's training curriculum. One commenter states that 
pilots must be made aware of the hazards of icing and that extended 
operation of an airplane in any icing encounter that results in 
significant airframe accretion of ice is unacceptable.
    The FAA does not concur that the AD's should be withdrawn based on 
the commenters' request. The FAA acknowledges that these AD's address 
an operational issue. When the requirements of these AD's are 
accomplished and the AFM limitations are revised, this material will be 
incorporated necessarily, as explained previously, into the training 
curriculum for the flight crews and dispatchers, if applicable, in the 
operator's approved training program. In this manner, pilots and 
dispatchers, if applicable, will be informed of the hazards of icing 
and that continued operation of an airplane in certain icing conditions 
is prohibited.

Comment 14. Request To Withdraw the Proposals: Require Training for Air 
Traffic Controllers and Weather Specialists

    Two commenters request that the FAA implement additional policy to 
require training for air traffic controllers and weather specialists in 
the recognition, avoidance, and procedures to exit severe icing 
conditions.
    The FAA does not concur that these AD's should be withdrawn. 
However, the FAA acknowledges that implementation of these AD's may 
necessitate additional training beyond that which is already required 
for air traffic controllers and weather specialists. The FAA may 
consider the need to provide training concerning recognition, 
avoidance, and procedures for exiting severe icing conditions. However, 
the intent of these AD's is to provide the flight crew with recognition 
cues for, and procedures for exiting from, severe icing conditions. The 
appropriate vehicle for requiring that such information be included in 
the AFM's is through issuance of an AD.

Comment 15. Request To Withdraw the Proposals: Add a Caution to the AFM

    One commenter requests that, in lieu of issuing the proposed AD's, 
a ``Caution'' should be added to the AFM to inform pilots to exit icing 
conditions if ice was observed to be forming aft of the protected 
surfaces of the wings. The commenter states that information regarding 
the use of flaps and the autopilot in icing conditions could also be 
incorporated into the AFM. The commenter does not indicate which 
section of the AFM should include this material.

[[Page 20654]]

    The FAA does not concur. The FAA finds that the requirement to exit 
severe icing conditions and information concerning use of the autopilot 
during flight in those conditions must be included in the Limitations 
Section of the AFM. Additionally, information concerning use of the 
flaps during those conditions should be included in the Procedures 
Section of the AFM. The appropriate vehicle for requiring these changes 
to the AFM is through issuance of an AD.

Comment 16. Request To Withdraw the Proposals: Require Alternative AFM 
Limitation

    One commenter requests that, in lieu of an AD, the FAA require an 
alternative AFM limitation that reads as follows: ``This aircraft is 
certified for flight into icing conditions as specified by Appendix C 
of Part 25. Actual icing encountered may be greater than Appendix C 
requirements.''
    The FAA does not concur. The suggested limitation does not provide 
guidance as to how a pilot can identify and safely exit icing 
conditions that have exceeded those specified in the icing envelope in 
Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part 
25). These AD's are intended to provide the flight crew with visual 
cues which indicate that icing conditions have exceeded the 
capabilities of the ice protection equipment, and with procedures to 
safely exit those conditions. No change to the AD's is necessary.

Comment 17. Request To Withdraw the Proposals: AFM Revisions Already 
Are Required

    One commenter requests that the proposals be withdrawn because 
section 121.133 (``Manual Requirements: `Preparation' '') of the 
Federal Aviation Regulations (14 CFR 121.133) already requires that 
operators incorporate revisions into the AFM's; therefore, issuance of 
the proposed AD's is unnecessary.
    The FAA does not concur. Section 121.133 of the Federal Aviation 
Regulations (14 CFR 121.133) does not specifically require that AFM's 
be updated to current revisions. Section 121.141 (``Airplane or 
Rotorcraft Flight Manual'') of the Federal Aviation Regulations (14 CFR 
121.141) requires that the current AFM be carried on the aircraft, but 
does not require incorporation of the most current revisions. 
Additionally, the commenter does not address the need to change the 
AFM's for airplanes that operate under parts 135 (``Air Taxi Operators 
and Commercial Operators'') and 91 (``General Operating and Flight 
Rules'') of the Federal Aviation Regulations (14 CFR parts 135 and 91). 
The appropriate vehicle for ensuring that the Limitations Section of 
the AFM's is changed is through issuance of an AD.

Comment 18. Request To Withdraw the Proposals: Use Existing AFM 
Revisions

    The General Aviation Manufacturers Association (GAMA), on behalf of 
its members, states that some of the affected manufacturers have 
prepared FAA-approved revisions for the AFM's for their products. GAMA 
indicates that those revisions incorporate specific information 
regarding cues for recognizing severe icing conditions and procedures 
for exiting such conditions, if encountered. Therefore, if the proposed 
AD's are adopted, the requirements of the AD's would supersede the 
information operators have already incorporated into the AFM's with 
less appropriate information that is not type design specific.
    One commenter, JAL, requests that certain existing AFM revisions 
for the affected Jetstream airplanes be cited in the proposed AD's for 
those airplanes in lieu of the content of the proposed AD's. (However, 
JAL does not request that the proposals be withdrawn for this 
particular reason.) JAL indicates that the existing AFM revisions have 
already been FAA-approved.
    The FAA does not concur with the commenters' requests. The FAA 
acknowledges that the AFM revisions required by these final rules will 
supersede previously approved AFM revisions. However, the FAA is 
unaware of any AFM that addresses all of the provisions specified in 
these final rules, nor of any AFM that contains specific visual cues 
that the FAA has not included in the final rules. Even if AFM material 
currently exists that does contain all of the provisions of the final 
rules, the FAA finds that issuance of an AD would still be necessary to 
mandate the provisions of the AFM revisions. However, the FAA would 
consider a request for approval of an alternative method of compliance, 
in accordance with the provisions of this AD, for those operators 
having AFM's that already contain all of the provisions of the final 
rules.
    Another commenter requests that the FAA withdraw the proposal that 
applies to Fairchild Model SA226 and SA227 series airplanes. The 
commenter states that the AFM for those airplanes currently contains 
visual cues to aid the flight crew in recognition of weather conditions 
conducive to SLD. This AFM also provides procedures for avoidance of 
such conditions. The commenter adds that these AFM procedures result in 
additional operating limitations on the aircraft with regard to severe 
weather conditions. The commenter believes these AFM procedures address 
all current FAA requirements.
    The FAA does not concur that the AFM for Fairchild Model SA226 and 
SA227 series airplanes addresses all of the proposed requirements of 
the proposed rule. For example, the Limitations section of the AFM for 
those airplanes does not require the flight crew to exit severe icing 
conditions. For this reason, the FAA does not consider the AFM for 
Fairchild Model SA226 and SA227 series airplanes to be equivalent to 
the information specified in these AD's.

Comment 19. Request To Withdraw the Proposals: Develop Rulemaking to 
Address Airplane Certification Outside of Appendix C

    Three commenters suggest that instead of arbitrarily prohibiting 
operation of the airplane, the FAA should undertake a well-designed 
research program and, if warranted, devise a rulemaking plan for 
certification of airplanes outside of Appendix C of part 25 of the 
Federal Aviation Regulations (14 CFR part 25). One commenter also 
suggests possible retroactive implementation of a new Appendix C.
    The FAA does not concur because of the length of time that would be 
required to implement the commenters' suggestion. The FAA finds that 
action is required prior to the commencement of the next icing season 
to prohibit the continued flight of airplanes in icing conditions that 
have been shown to be unsafe and for which the airplanes have not been 
certificated. However, the FAA is currently considering initiating an 
assessment of the need to revise Appendix C and the possibility of its 
retroactive implementation.
    Transport Canada Aviation states that the FAA has determined that 
there may be a problem with the certification requirements for icing on 
de Havilland Model DHC-6, DHC-7, and DHC-8 series airplanes, but not 
the specific approval or design features of those airplanes. However, 
the commenter does not specifically request that the proposals be 
withdrawn.
    The FAA does not concur with the commenter's statement. The FAA has 
only determined that no adequate means exists for the flight crew to 
determine when the icing certification limits have been exceeded. The 
purpose of these AD's is to provide more clearly defined procedures and 
limitations

[[Page 20655]]

associated with severe icing conditions. This does not imply that the 
certification requirements for icing are inadequate.

Comment 20. Request To Withdraw the Proposals: Issue a ``General AD'' 
for All Airplane Types

    One commenter requests that a ``general AD'' be issued to prohibit 
all airplane types from inadvertent flight into hazardous SLD 
conditions. Another commenter adds that if encounters with freezing 
rain/freezing drizzle conditions must be reported to Air Traffic 
Control, such reporting also should apply to flight crews of all 
airplane types.
    The FAA does not concur with the commenter's request. For the 
reasons discussed earlier in the preamble of this AD, the FAA has 
determined that airplanes having pneumatic deicing boots and unpowered 
aileron controls are of immediate concern and have been addressed as a 
higher priority. The FAA finds that action is required prior to the 
commencement of the next icing season to prohibit the operation of 
these airplanes in icing conditions that have been shown to be unsafe 
and for which the airplanes have not been certificated. However, the 
FAA is currently considering initiating an assessment of the potential 
adverse effects of SLD on all airplane types.

Comment 21. Request To Withdraw the Proposals: Establish a Detailed 
Reporting System

    One commenter requests that the FAA establish a detailed reporting 
system for inadvertent encounters with severe SLD. The commenter 
envisions a system that would provide a database for better 
identification of controllability issues and visual indications related 
to these encounters.
    The FAA does not concur with the commenter's request. The FAA has 
been advised that the Regional Airline Association (RAA) has already 
established an ``Unusual Icing Reporting Program'' for the purpose 
described by the commenter; therefore, establishing another reporting 
program would duplicate this benefit.

Comment 22. Request To Withdraw the Proposals: Revise the Master 
Minimum Equipment List (MMEL)

    Two commenters request that, instead of addressing an MMEL item in 
an AD [i.e., the icing detection lights referenced in paragraph (a)(1) 
of the proposals], the FAA should require that the MMEL be revised. A 
third commenter adds that the decision to change the MMEL should be 
made by FAA Operations Inspectors based on local conditions. One 
commenter states that the prohibition of dispatch with any inoperative 
ice detection lights would preclude any efforts by an operator to 
enhance safety by installing a second set of bulbs. The commenter adds 
that under this proposed rule, this type of action would be penalized 
by simply doubling the chances of a burned out bulb grounding the 
aircraft. In practice, if one were to add a fully redundant set of 
bulbs, it would enhance safety by allowing the equivalent of the 
current illumination level even with a bulb burned out.
    The FAA does not concur with these requests. FAA Operations 
Inspectors are not authorized to make MMEL revisions. The FAA has 
determined that it is prudent to address the icing detection lights in 
these final rules to ensure uniform and immediate application of the 
requirements of the AD's. Concerning the example provided by one of the 
commenters, if an operator chooses to add a fully redundant set of 
bulbs, that operator should request approval of an alternative method 
of compliance in accordance with the provisions of this final rule.
    Although Transport Canada Aviation does not request that the 
proposals be withdrawn, it requests a revision to the requirement that 
all icing detection lights must be operative. For de Havilland Model 
DHC-7 and DHC-8 series airplanes, the commenter requests that the 
requirement be changed to mandate that at least one outboard and one 
inboard inspection light be operative prior to flight into known or 
forecast icing conditions at night. Since the MMEL contains a provision 
that a suitable lamp/light of adequate capacity be available, this is 
considered acceptable in conjunction with other indications of freezing 
rain or freezing drizzle. Similarly, for de Havilland Model DHC-6 
series airplanes, the requirement should be revised to require a 
suitable lamp/light for dispatch at night with one wing inspection 
light inoperative.
    The FAA does not concur. The FAA has determined that the 
justification provided by the commenter is not adequate to enable the 
FAA to determine if the proposed changes are acceptable. During severe 
icing conditions, the flight crew's workload may be high, and there may 
be no opportunity to use the portable lamp/light, which, in itself, may 
create disorientation in the cockpit due to adverse reflections from 
the glass. The FAA's intent in having all inspection lights be 
operative at night is to provide the flight crew the best possible 
visibility of the airframe. However, the FAA would consider a request 
for approval of an alternative method of compliance, in accordance with 
the provisions of these AD's, provided that adequate justification is 
presented to support such a request.

Comment 23. Request To Withdraw the Proposals: Certify Airplanes for 
Flight in Conditions Outside Appendix C

    One commenter implies that the airplanes affected by the proposed 
rules must be rectified to a level beyond the present certification 
requirements for flight in icing.
    The FAA does not concur. The final rules do not require 
certification of the airplane beyond the current certification 
requirements for flight in icing specified in Appendix C. These AD's 
simply provide the flight crew with visual cues which indicate that 
icing conditions have exceeded the capabilities of the ice protection 
equipment, and with procedures to safely exit those conditions.
    One commenter requests that the proposal for de Havilland Model 
DHC-6 series airplanes be withdrawn because this airplane model is type 
certificated in Canada, which is a country with a higher standard than 
the United States for operating in icing conditions.
    The FAA does not concur. This commenter did not submit data to the 
FAA to substantiate that the airplane has been shown to be safe for 
flight outside the icing certification envelope specified in Appendix 
C. Additionally, the FAA is unaware of any foreign civil aviation 
authority having certification requirements for icing conditions that 
are outside of the icing certification envelope used in the United 
States.

Comment 24. Request To Withdraw the Proposals: Proposals Prohibit 
Takeoff or Approach in ``Light Freezing Drizzle'' Conditions

    One commenter requests the proposals be withdrawn because the 
proposed limitation would prohibit takeoff or approach when ``light 
freezing drizzle'' conditions that are caused by light precipitation 
falling through a thin layer of cold surface air below warmer air above 
are reported on the surface. The commenter maintains that with 
accomplishment of the appropriate ground deicing precautions prior to 
takeoff, no hazard to the operation of the airplane is posed.
    The FAA does not concur that the AD's should be withdrawn for this 
reason. These AD's do not affect any existing regulations or FAA-
approved operating procedures related to takeoff, dispatch, or release 
of an airplane in icing conditions, nor do these AD's

[[Page 20656]]

prohibit operation in specific meteorological conditions. These AD's 
only prohibit remaining in icing conditions when certain visual cues 
are present on the airplane. Operators must comply with existing rules 
that require an airplane to be free of ice prior to takeoff. Therefore, 
takeoff in ``light freezing drizzle'' would only be prohibited by 
existing regulations or FAA-approved operating procedures, not by these 
AD's. As explained previously, the FAA considers that landing the 
airplane when freezing rain/freezing drizzle conditions are encountered 
would, in many cases, be the most expeditious method of exiting the 
conditions. Such landing would be in compliance with the limitation 
that requires the flight crew to exit the severe icing conditions.

Comment 25. Request To Withdraw the Proposals: Proposals Leave 
Unanswered Questions

    One commenter contends that the proposals leave unanswered 
questions. The commenter alleges that without the answers to those 
questions, affected parties are deprived of the ability to provide 
informed comments and, thereby, are ``denied their rights under the 
Administrative Procedures Act (APA) to comment on the proposed rules.'' 
Specifically, the commenter asks:

--What is unusual icing?
--Does the pilot, Air Traffic Control, dispatch, or the FAA determine 
when the conditions exist?
--What is splatter effect?
--Where are the operating instructions incorporated--in the AFM, 
training manuals, or some other document?

The FAA infers from the commenter's remarks that the commenter requests 
the proposed AD's be withdrawn because informed comments could not be 
provided.
    The FAA does not concur that the AD's should be withdrawn on this 
basis. The FAA does not agree that the public has been deprived of the 
ability to provide informed comments, as required by the APA. In 
general, the APA requires that notice of the terms or substance of a 
proposed rule be published in the Federal Register. The purpose of this 
requirement is to ensure that federal agencies thoroughly consider all 
information and opinions submitted by the public before any 
requirements are imposed. Notice is intended to improve both the 
quality of the regulations and their acceptability to the public. The 
FAA finds that none of the questions raised by the commenter identify 
areas in which the commenter has not been provided a reasonable 
opportunity to comment. The fact that the commenter raises questions 
suggests that the commenter considers a need for further clarification. 
Even if the commenter is correct in that these questions require 
clarification, that fact in itself is a comment that can be addressed 
properly by simply clarifying terms. The fact that clarification is 
necessary does not mean that the public has been denied reasonable 
opportunity to comment.
    In response to the commenter's questions, the FAA provides the 
following clarification. The term ``unusual icing'' did not appear in 
the proposed rules. However, the phrase ``unusually extensive ice'' is 
referenced in paragraph (a)(1) of the final rules. [This reference 
appears in paragraph (a)(2) of the final rule for Aerospatiale 
airplanes.] ``Unusually extensive ice'' accrued on the airframe in 
areas not normally observed to collect ice is a visual cue that is 
subject to interpretation by the flight crew; therefore, a specific 
definition of ``unusually extensive ice'' cannot be provided.
    These AD's address changes to AFM limitations, which pertain to the 
pilot since the pilot is responsible to look for the visual cues 
defined in the AD's. Therefore, the pilot determines when severe icing 
conditions exist.
    The terminology ``splatter effect'' did not appear in the proposed 
rules. The FAA infers from the commenter's question that the commenter 
is referencing terminology used in paragraph (a)(2) of the proposed 
AD's. ``Droplets that splash or splatter on impact at temperatures 
below +5 degrees Celsius OAT'' is a visual cue that was included in the 
proposed AD's as a method of identifying severe icing conditions.
    Concerning incorporation of operating instructions, these final 
rules specify that the AFM's be revised. The AD's do not specify that 
any other manuals or documents be revised. However, information that is 
included in the AFM as a limitation is necessarily included in the 
training program.

Comment 26. Request To Clarify Scope of Icing Conditions Addressed

    Transport Canada Aviation suggests that the proposals, which 
address only freezing rain/freezing drizzle conditions, are not 
adequate to cover all hazards related to operation of aircraft in icing 
conditions. The commenter makes no specific request.
    The FAA concurs that these AD's do not address all icing related 
hazards. The FAA's intent is to minimize the potential hazards 
associated with operating the airplane in severe icing conditions by 
providing the flight crews with more clearly defined procedures and 
limitations associated with such conditions. However, no change to the 
final rules is necessary.

Comment 27. Request To Expand the Applicability of the AD's

    One commenter, the CAA, suggests that the ``coverage'' of the 
proposals should be stated clearly. The CAA believes that a restriction 
to those operations in ``regularly scheduled passenger service'' is not 
warranted for a safety issue as it does not cover cargo, charter, or 
private operations. The commenter does not specify which airplane 
models should be addressed. The FAA infers from the commenter's remarks 
that it requests that the proposed AD's be applicable to other airplane 
models that are used in cargo, charter, or private operations that may 
have been excluded from the applicability of these AD's.
    The FAA does not concur that the applicability of these AD's should 
be expanded to include additional airplane models used primarily in 
cargo, charter, or private operation. The FAA is currently considering 
the need for additional rulemaking to address other airplane models 
having pneumatic deicing boots and unpowered aileron controls that are 
used in these types of service that were not addressed by these AD's. 
Additionally, the applicability of these final rules indicates that the 
AD's apply to ``all'' of the airplane models identified, certificated 
in any category. This means that the AD's apply to all of the affected 
airplanes, regardless of how those airplanes are operated (including 
passenger service, cargo, charter, or private operation).

Comment 28. Request for Design Changes to the Airplanes

    One commenter requests that the FAA require design changes to the 
airplanes, which, when accomplished, will allow elimination of the AFM 
limitations. The commenter states that abnormal roll control anomalies 
could be eliminated by design changes that prevent any ice shapes from 
forming by using supplemental ice protection added to existing 
pneumatic boots or other ice protection installations. The commenter 
concludes that, given this added protection, restricting flight in 
freezing drizzle could be reduced to allow exposure to these 
atmospheric conditions for a reasonable time and would not require 
immediately exiting these conditions when encountered as presently 
stipulated.

[[Page 20657]]

    The FAA does not concur that it should require design changes to 
airplanes in these AD's. Currently, the FAA is unaware of any design 
changes that would allow elimination or reduction of the AFM 
limitations specified in these AD's. However, if such design changes 
are developed, approved, and become available, the FAA would consider 
additional rulemaking to require such changes. The FAA finds that even 
if the ice protection system prevented the formation of ice shapes in 
front of the ailerons when the airframe is exposed to certain freezing 
drizzle conditions, other meteorological conditions still exist (e.g., 
freezing rain) for which the airplane would not be certificated.

Comment 29. Request for More Specific Visual Cues

    One commenter requests that the FAA provide more specific visual 
cues for identification of freezing rain or freezing drizzle 
conditions. The commenter states that the generic visual cues provided 
in the proposed AD's are not adequate for aircraft types that 
frequently operate in and encounter SLD conditions. For example, ice 
could be forming on the upper wing and not the lower wing; therefore, 
looking at the lower wing would not be a reliable visual cue. Two 
commenters suggest that specific visual cues be provided for each 
airplane model. One of these commenters states that subjective cues may 
be of limited benefit if the pilot's experience with icing is 
inadequate. The other commenter adds that subjective visual cues will 
result in varying interpretations (i.e., some unnecessary course 
changes in altitudes or service interruptions caused by overly 
conservative interpretations). Transport Canada Aviation does not 
request more specific visual cues; but states that ``unusually 
extensive ice,'' ``normally observed,'' and ``farther back than 
normally observed'' are all variable terms that are largely dependent 
on flight crew experience. The commenter contends that limitations and 
procedures described using these terms will not be consistently 
interpreted. In addition, Transport Canada Aviation states that ice on 
the lower wing surface aft of the protected area, by itself, is 
unlikely to cause a hazard. Moreover, the presence or absence of such 
ice cannot be used as an indication of any hazardous accumulation on 
the upper wing surface or on the horizontal stabilizer.
    The FAA does not concur with the commenters' request to provide 
more specific (or airplane-specific) visual cues. The FAA agrees with 
the commenters' assertion that, under certain circumstances, 
examination of the undersurface of a high wing may not be reliable. The 
FAA also agrees that other cues, such as unusually extensive ice 
accrued on the airframe in areas not normally observed to collect ice 
and accumulation of ice on the propeller spinner farther aft then 
normally observed, are subjective and that reliance on pilot judgment 
and experience is necessary in such cases. Additionally, the FAA fully 
supports the development and use of airplane-specific cues by operators 
and manufacturers. Unfortunately, no commenter provided airplane-
specific cues during this comment period.
    In summary, the FAA finds that the combined use of the generic cues 
provided and the effect of the final rules in increasing the awareness 
of pilots concerning the hazard of operating outside of the 
certification icing envelope will provide an acceptable level of 
safety. However, for those operators that elect to identify airplane-
specific visual cues, the FAA would consider a request for approval of 
an alternative method of compliance, in accordance with the provisions 
of this AD.
    Transport Canada Aviation states that the term ``protected area'' 
may not be readily recognizable by the flight crew; for example, not 
all of a deicing boot surface is ``protected area.'' [This terminology 
appears in the second visual cue (in the proposals for airplanes other 
than Aerospatiale airplanes) and in the autopilot limitation in 
paragraph (a)(1) of the proposals. For Aerospatiale airplanes, this 
terminology appears in the secondary indications in paragraph (a)(1) of 
the proposal.] The FAA infers that the commenter requests that more 
specific language than ``protected area'' be used.
    The FAA does not concur that this terminology should be revised. 
The FAA considers that a pilot understands that a portion of the 
deicing boot would be considered to be unprotected. Therefore, no 
additional clarification or definition of the term ``protected area'' 
is necessary.

Comment 30. Request to Reference Clear Icing Conditions and Clear 
Component of Mixed Icing Conditions

    One commenter also asks that all references to freezing rain and 
freezing drizzle environments and visual cue identification reference 
clear icing conditions and the clear component of mixed icing 
conditions. According to the commenter, mixed icing conditions can 
contain areas of freezing rain and/or freezing drizzle. The commenter 
notes that mixed icing has taken on two different definitions within 
the aviation community--the ``engineering'' definition (which is 
defined in an FAA icing handbook) and the definition pilots use (which 
includes areas of clear and rime ice). The commenter states that a 
clear definition of these conditions is needed. The commenter adds that 
only pilot reports can show that freezing rain/freezing drizzle exists 
because forecasting of these conditions is inadequate. The commenter 
indicates that while the Aerospatiale airplanes have side window cues 
that will accurately identify freezing rain or freezing drizzle, pilots 
of other airplanes without such a sophisticated cue may erroneously 
report mixed icing.
    The FAA does not concur. The FAA acknowledges that freezing rain 
and freezing drizzle may be reported as clear/mixed icing conditions. 
However, the flight crew must exit icing conditions that produce the 
visual cues specified in the final rules. Exiting the icing conditions 
is not dependent upon the terminology used to describe the conditions. 
Therefore, the FAA has determined that it is not necessary to include 
references to clear icing conditions and the clear component of mixed 
icing conditions. In addition, the FAA has determined that including a 
discussion in these AD's of the phenomenon of mixed icing conditions as 
it relates to the current state-of-the-art weather forecasting would be 
premature because no clear definition of this phenomenon has been 
agreed upon among the aviation community. The FAA is currently 
considering an assessment during which various icing-related subjects, 
including mixed icing conditions, would be addressed.

Comment 31. Request for Research and Use of Wing-Mounted Ice Detectors

    One commenter requests that wing-mounted ice detectors, which 
provide real-time icing severity information (or immediate feedback) to 
flight crews, continue to be researched and used throughout the fleet. 
The FAA infers from this commenter's request that the commenter asks 
that installation of these ice detectors be mandated by the FAA.
    While the FAA supports the development of such ice detectors, the 
FAA does not concur that installation of these ice detectors should be 
required. The specifications for automatic detectors having the 
capabilities to differentiate among freezing rain, freezing drizzle, 
and other icing conditions have not been determined. However, if such 
ice detectors are

[[Page 20658]]

developed, approved, and become available, the FAA may consider further 
rulemaking action to require installation of such equipment.

Comment 32. Request to Limit the Applicability of the AD's

    One commenter requests that the applicability of the proposals be 
limited to airplanes having NACA 430xx airfoils. The commenter asserts 
that the unusual pressure peak on the NACA 430xx airfoils at 9 percent 
chord caused the ice ridge to form at that point, which resulted in the 
accident involving a Aerospatiale Model ATR-72 series airplane. The 
commenter states that ``the accident was caused by the poorly designed, 
unusual, and fortunately rarely used NACA 430xx airfoils used on this 
airplane.''
    The FAA does not concur with the commenter's request to limit the 
applicability of the AD's. First, the National Transportation Safety 
Board (NTSB) has not yet made an official finding of the probable cause 
of the accident referenced by the commenter. Therefore, the FAA cannot 
assume that airplanes having NACA 430xx airfoils are more susceptible 
to the addressed unsafe condition than those airplanes that do not have 
this type of airfoil. Second, the FAA has examined the data submitted 
by the commenter, and disagrees with the commenter's assertion 
concerning the formation of ice ridges. The formation of ice ridges 
depends on many factors. Ice ridges have been observed to form in areas 
where there is no pressure (commonly, ``suction'') peak. However, the 
impingement location of large droplets is more relevant to the 
development of ice ridges than the particular pressure distribution. 
The commenter does not address the fact that, regardless of the type of 
airfoil on an airplane, a substantial sharp edge protuberance in the 
vicinity of the suction peak can have adverse consequences to the 
aerodynamic performance of the airfoil. Regardless of the cause of 
location of ice formations, prevention or removal of the ice is 
certainly an acceptable remedy for such conditions, should those 
conditions occur. For example, Aerospatiale extended the deicing boots 
to prevent the formation of adverse ice ridges.

Comment 33. Request for Approval of Improved Deicing Equipment for 
Aerospatiale Airplanes

    ATR requests that paragraph (b) of the proposed rule for 
Aerospatiale airplanes be revised to indicate that installation of any 
improved version of deicing equipment that is approved by the FAA is 
acceptable for compliance with the requirements of that paragraph. The 
commenter provides no justification for its request.
    The FAA does not concur with the commenter's request to revise the 
AD. However, if an improved version of deicing equipment is developed, 
approved, and available, the FAA would consider a request for approval 
of an alternative method of compliance, in accordance with the 
provisions of the AD.

Comment 34. Request for Re-Evaluation of Modified Deicing Boots on 
Aerospatiale Airplanes

    In response to the proposal for Aerospatiale airplanes, one 
commenter requests that the new, enlarged deicing boots that are 
required to be installed on these airplanes must be re-evaluated before 
total confidence in the modified boots is warranted. The commenter 
asserts that no test data exist to show that the modified boots will 
preclude the problem of large droplets outside of Appendix C. The area 
of exposure outside of Appendix C is essentially open-ended, and only 
limited testing within a narrow range of droplet diameters was 
conducted. Additionally, the test conditions that existed during the 
tanker testing conducted at Edwards Air Force Base, which was intended 
to be a ``before modification/after modification'' validation program, 
were not identical. The commenter adds that no modification will ensure 
that any airplane is safe while flying in icing conditions outside 
those specified in Appendix C.
    The FAA does not concur with the commenter's request for a re-
evaluation of the modified deicing boots. The modified deicing boots 
for these airplanes were subjected to an extensive certification 
program by both the FAA and the Direction Generale de l'Aviation Civile 
(DGAC), which is the airworthiness authority for France. FAA approval 
of the modified boots was based on engineering analyses, wind tunnel 
testing, flight testing in natural icing conditions, and a validation 
program involving a United States Air Force icing tanker. This testing 
verified that the modified boots continue to perform the intended 
function within the Appendix C icing envelope. In addition, the 
extended deicing boots were shown to adequately protect the airplane 
from the larger, supercooled water droplets that are believed to have 
existed in the area at the time of the accident in October 1994.
    It should be noted, however, that it is not intended that the 
modified boots provide protection in all possible icing conditions, 
including freezing rain/freezing drizzle. However, the FAA considers 
that the combination of the enlarged deicing boots, the AFM operational 
procedures and restrictions, and the visual cues which indicate entry 
into freezing rain/freezing drizzle conditions provides for an enhanced 
level of safety during inadvertent flight in these conditions.

Comment 35. Request for Formal Weather Forecasting System for Freezing 
Rain/Freezing Drizzle

    One commenter supports a requirement to establish a formal system 
to provide forecasts of freezing rain/freezing drizzle conditions, as 
proposed in paragraphs (b) and (c) of the original proposed rule for 
Aerospatiale airplanes. [This proposed requirement was removed from the 
subsequent supplemental notice of proposed rulemaking (NPRM) issued for 
these airplanes in January 1996.] The commenter states that such a 
requirement should remain in effect until forecasting tools are 
developed or detection methods are established to prevent dispatch or 
operations in conditions outside those specified in Appendix C. The 
commenter states that the efficacy of the deicing boots has not been 
shown completely nor documented; therefore, avoidance of freezing rain/
freezing drizzle is paramount to safety of flight.
    The FAA does not concur that such a requirement is necessary. The 
FAA agrees that such a system would enhance the safety of flight 
operations. However, there is no evidence that lack of a system with 
such specialized features would lead to an unsafe condition. Forecasts 
of freezing rain/freezing drizzle are a normal part of pre-flight 
weather briefings. The FAA is aware, however, of serious limitations 
for such a system to provide accurate and timely forecasts of these 
conditions during flight in areas that are removed from weather 
reporting stations. Quite often, the only indication of the existence 
of severe icing conditions is from pilot reports or other direct 
observations.
    Research is underway currently in industry and the academic 
community to address shortcomings in the forecasting of severe icing 
conditions. The FAA may consider further rulemaking if advancements in 
weather forecasting provide for a reliable method to predict the 
occurrence of freezing rain/freezing drizzle conditions during flight 
or in areas removed from direct observations.

[[Page 20659]]

Comment 36. Request To Approve Earlier Service Bulletin Revisions

    One commenter to the proposed rule for Aerospatiale airplanes 
requests that the proposed AD be revised to specify that earlier 
revisions of service bulletins are acceptable for compliance with the 
requirements of the proposed rule. The commenter makes this request so 
as to eliminate the need to apply for approval of alternative methods 
of compliance when accomplishing service bulletin revisions other than 
those specified in the proposed rule.
    The FAA does not concur that earlier revisions of the referenced 
service bulletins should be cited in the final rule for Aerospatiale 
airplanes. However, the FAA would consider a request for approval of an 
alternative method of compliance, in accordance with the provisions of 
the AD, provided that adequate justification is presented to support 
such a request.
    Additionally, the FAA has revised the revision levels specified for 
certain service bulletins because those revision levels were omitted 
inadvertently from paragraph (b) of the proposed rule for Aerospatiale 
airplanes. That final rule has been revised to indicate that certain 
modifications are to be accomplished in accordance with Revision 1 of 
Aerospatiale Service Bulletins ATR42-57-0043, ATR72-57-1015, and ATR72-
57-1016. The correct date for Revision 1 of those service bulletins 
(April 10, 1995) was specified in the proposal for the affected 
airplanes.

Comment 37. Request To Revise Referenced Service Bulletins

    One commenter to the proposal for Aerospatiale airplanes suggests 
that service bulletin revisions should contain a statement indicating 
that the revision has no effect on previously modified airplanes. The 
commenter provides no justification for this request.
    The FAA acknowledges that many service bulletins do contain the 
suggested phrase as an aid to operators that may already have 
accomplished an earlier service bulletin revision. In fact, if a 
particular service bulletin is specified in an AD and that service 
bulletin is revised, the FAA routinely determines whether the service 
bulletin revision adequately addresses the unsafe condition specified 
in the AD; if necessary, the FAA amends the AD to cite the later 
service bulletin revision.

Comment 38. Request To Revise Visual Cue: Ice on Side Window

    One commenter suggests revised wording for the first visual cue 
specified in paragraph (a)(1) of the proposed rule for Aerospatiale 
airplanes, as follows: ``Freezing rain and freezing drizzle are 
characterized by ice covering all or a substantial part of the unheated 
portion of either forward side window and/or water splashing or 
streaming on the windshield or the side window when in freezing or near 
freezing temperatures.'' The commenter states that the present wording 
implies that ice will always appear on the side window; however, this 
is not the case.
    The FAA does not concur with the commenter's request. The 
commenter's revised wording suggests that water splashing or streaming 
on the windshield or the side window would be a primary cue used to 
determine when severe icing conditions are present. The FAA does not 
concur that water splashing or streaming on the windshield or the side 
window would be a reliable cue in itself. However, this cue may be used 
as a supplemental cue to the primary cue of ice accruing on the side 
window. No change to the final rule for Aerospatiale airplanes is 
necessary.

Comment 39. Request To Remove Visual Cue: Unusually Extensive Ice 
Accretion

    One commenter, Saab, requests that if the FAA does not withdraw the 
proposed AD's, paragraph (a)(1) of the proposal for Saab SF340A and 
SAAB 340B series airplanes should be revised. The commenter suggests 
that the first visual cue that appears in that paragraph, which relates 
to unusually extensive ice accretion, be removed from the proposal for 
those airplanes. Saab indicates that critical ice is believed to be ice 
that builds up beyond the protected surfaces on the wing. On Saab Model 
SF340A and SAAB 340B series airplanes, the pilot has a good view of the 
outer wing and the propeller spinner. Unusually extensive ice in other 
areas may or may not be significant in determining whether freezing 
rain or freezing drizzle is present; however, the primary visual cue 
for these airplanes is ice on the spinner/outer wing.
    In light of Saab's remarks, the FAA concurs that the visual cue 
addressed by the commenter should be removed from the final rule for 
Saab Model SF340A and SAAB 340B series airplanes. (That visual cue 
remains in place for Saab Model SAAB 2000 series airplanes.) Paragraph 
(a)(1) of that final rule has been revised accordingly.
    A second commenter, Raytheon, requests that the same visual cue be 
removed from the proposal for Beech airplanes. Raytheon indicates that 
it does not believe that observation of this visual cue indicates that 
the airplane has exceeded the Appendix C icing envelope with respect to 
Beech airplanes. Therefore, the cue specified in the proposal would be 
irrelevant in an AFM for these airplanes.
    The FAA does not concur with Raytheon's request. The commenter has 
not submitted data to warrant removal of the visual cue. No change to 
the final rule for Beech airplanes has been made.

Comment 40. Request To Remove Visual Cue: Accumulation of Ice on Wing 
Surfaces

    JAL requests that the FAA remove the generic information contained 
in the visual cue concerning accumulation of ice on the wing surfaces 
from the proposals for Jetstream airplanes. JAL indicates that, for its 
airplanes, the appropriate visual cue is the accretion of ice behind 
the protected area of the wing upper surface (not the wing lower 
surface).
    The FAA concurs. The FAA finds that this particular visual cue 
should be airplane-specific. Therefore, the FAA has customized 
paragraph (a)(1) of the final rules for all affected airplanes to 
specify whether accumulation of ice is observed on the upper or lower 
surface of the wing, depending upon whether the airplane is a high- or 
low-wing airplane. [Operators should note that, for Aerospatiale 
airplanes, the cue was customized in paragraph (a)(2) of the final 
rule.]

Comment 41. Request To Revise Visual Cue: Accumulation of Ice on 
Propeller Spinner

    One commenter requests that the FAA revise the visual cue 
concerning accumulation of ice on the propeller spinner, as specified 
in paragraph (a)(1) of the proposals. For consistency, the commenter 
requests that the word ``back'' be replaced with ``aft.''
    The FAA concurs with the commenter's request. The final rules have 
been revised to change the visual cue to read as follows: 
``Accumulation of ice on the propeller spinner farther aft than 
normally observed.'' [Operators should note that, for Aerospatiale 
airplanes, this change appears in paragraph (a)(2) of the final rule.]

Comment 42. Request To Remove Visual Cue: Accumulation of Ice on 
Propeller Spinner

    One commenter, JAL, requests that the FAA remove the visual cue 
concerning accumulation of ice on the propeller spinner from the 
proposals for Jetstream airplanes. JAL indicates that on Jetstream 
Model ATP airplanes and Model 748 series airplanes, the propeller 
spinner is not visible from the

[[Page 20660]]

flight deck. On Jetstream Model 3101, 3201, and 4101 airplanes, the 
propeller spinner is visible from the flight deck, but flight test 
experience indicates that there is no unique correlation between the 
extent of spinner ice accretion and the existence of freezing rain/
freezing drizzle conditions.
    The FAA concurs partially. The FAA concurs that since the propeller 
spinner is not visible from the flight deck on Jetstream Model ATP 
airplanes and Model 748 series airplanes, the visual cue can be removed 
from paragraph (a)(1) of the final rules for these models. The FAA does 
not concur that this visual cue should be removed from the AD's for 
Jetstream Model 3101, 3201, and 4101 airplanes. The commenter did not 
submit data to substantiate its assertion that flight test experience 
indicates there is no unique correlation between the extent of spinner 
ice accretion and the existence of freezing rain/freezing drizzle 
conditions. Therefore, it is uncertain if the commenter's flight test 
airplane was equipped with instrumentation that would allow the 
detection and/or measurement of droplets outside the Appendix C 
conditions, and if the airplane had flown into icing conditions 
containing freezing rain or freezing drizzle.

Comment 43. Request To Remove Limitation to Immediately Exit Freezing 
Rain/Freezing Drizzle

    Saab requests that the FAA remove a sentence from paragraph (a)(1) 
of the proposals that requires the pilot to immediately exit freezing 
rain or freezing drizzle conditions by changing altitude or course. 
This commenter points out that the first limitation contained in the 
proposal for Saab airplanes (``Flight in meteorological conditions 
described as freezing rain or freezing drizzle, as determined by the 
following visual cues, is prohibited * * *'') already prohibits flight 
in these conditions, and the pilot should respond accordingly. Raytheon 
believes a conflict exists between using observations of ice accretion, 
as required by paragraph (a)(1) of the proposed rules, and the 
``determination'' of certain meteorological conditions.
    The FAA concurs partially. The FAA does not agree that the sentence 
discussed by Saab should be removed from paragraph (a)(1) of the final 
rules. As explained previously, the first limitation in paragraph 
(a)(1) of the final rules has been revised to read: ``During flight, 
severe icing conditions that exceed those for which the airplane is 
certificated shall be determined by the following visual cues. If one 
or more of these visual cues exist, immediately request priority 
handling from Air Traffic Control to facilitate a route or an altitude 
change to exit the icing conditions.'' (This wording is slightly 
different in the final rule for Aerospatiale airplanes because only one 
visual cue is provided.) The FAA finds that this revision to the final 
rules addresses the commenters' concerns with regard to the proposed 
limitations.
    One commenter poses various questions concerning the last sentence 
of the first instruction listed in the procedures for exiting the 
freezing rain/freezing drizzle environment in paragraph (a)(2) of the 
proposals. (That sentence reads as follows: ``Asking for priority to 
leave the area is fully justified under these conditions.'')

--What does the term ``priority'' provide a pilot when asking for 
priority to leave icing conditions?
--What if there were three simultaneous requests for ``priority?''
--What Air Traffic Control procedures exist for treating an immediate 
request for ``priority?''
--Where is the term ``priority'' defined?

The commenter states that confusion over terms that have not been 
defined clearly by the FAA has partially resulted in accidents and 
incidents. However, the commenter does not cite a specific case in 
which this occurred.
    The FAA has re-examined the last sentence of the first instruction 
listed in the procedures for exiting the freezing rain/freezing drizzle 
environment in paragraph (a)(2) of the proposals. The FAA has 
reconsidered use of the term ``priority.'' The FAA finds that more 
appropriate language that would be understood clearly by the flight 
crew and Air Traffic Controllers should be used in that instruction. 
Existing training for flight crews and Air Traffic Controllers 
addresses priority handling of airplanes. However, the FAA will issue 
additional information for Air Traffic Controllers to further clarify 
priority handling of airplanes in severe icing conditions. The FAA 
finds that the limitations specified in paragraph (a)(1) of the final 
rules will result in the pilot taking appropriate steps to exit the 
icing conditions. Therefore, the FAA finds that the sentence questioned 
by the commenter may be removed from the final rules without affecting 
safety. Accordingly, the FAA has removed that sentence from the final 
rules.
    Additionally, in order to use terminology in the procedures for 
exiting the severe icing environment that is consistent with the 
terminology used in the revised limitation and to simplify certain 
language, the FAA has revised the first instruction of the procedures. 
The revised instruction reads as follows: ``Immediately request 
priority handling from Air Traffic Control to facilitate a route or an 
altitude change to exit the icing conditions in order to avoid extended 
exposure to flight conditions more severe than those for which the 
airplane has been certificated.''

Comment 44. Request To Change the Note Concerning the Autopilot

    One commenter, ATR, requests that the FAA revise the second note in 
paragraph (a)(1) of the proposal for Aerospatiale airplanes. As 
proposed, ATR believes the last sentence of the note is too 
restrictive. ATR proposes the following: ``The autopilot may mask 
tactile cues * * * characteristics. Therefore, when any ice is visible 
on the airplane, the pilot should consider flying manually for short 
periods in order to check the absence of any anomaly.''
    Two commenters request that the FAA remove a similar note 
concerning the autopilot from the proposals for airplanes other than 
Aerospatiale models. One of the commenters, JAL, states that the note 
contains advisory information and should not appear in the Limitations 
Section of an AFM.
    The FAA concurs with ATR's comment that the last sentence of the 
note is too restrictive; that sentence has been removed from the final 
rules for all airplanes. However, the FAA does not agree with JAL's 
contention that the explanation of the relationship between the 
autopilot and the masking of tactile cues is inappropriate for 
insertion in the Limitations Section of an AFM. On the contrary, the 
FAA finds that inclusion of such information will increase the level of 
understanding and, consequently, will increase the level of safety.
    In light of this, the FAA finds that the note may be removed from 
paragraph (a)(1) of the final rules for all airplanes; however, the 
information contained in the first sentence of that note has been 
combined with the autopilot limitation in paragraph (a)(1) of the final 
rules. The final rules have been revised accordingly.

Comment 45. Requests to Remove Autopilot Limitation

    Saab requests that the FAA revise the second limitation that 
appears in paragraph (a)(1) of the proposal for Saab airplanes. As 
proposed, this limitation indicates that use of the autopilot is 
prohibited when any ice is observed forming aft of the protected 
surfaces of

[[Page 20661]]

the wing, or when unusual lateral trim requirements or autopilot trim 
warnings are encountered. Saab asks that this autopilot limitation be 
modified to take into consideration the autopilot system design on 
these airplanes, which provides out-of-trim warnings; therefore, the 
autopilot can be used up to the point where a warning is triggered. 
Saab adds that the triggering point is early enough for the warning to 
be taken, should the reason be ice build-up beyond the protected 
surfaces. Additionally, there is no automatic disconnect if the 
autopilot servo reaches its limit torque, which would prevent any 
surprise to the pilot during an out-of-trim condition.
    Another commenter, EMBRAER, requests that use of the autopilot not 
be limited for EMBRAER Model EMB-120 series airplanes. The commenter 
states that flight tests have demonstrated the safe ability of these 
airplanes to depart a freezing rain/freezing drizzle condition with the 
autopilot on.
    Raytheon also objects to the autopilot limitation. Raytheon 
suggests that a better approach is to inform the pilots of the nature 
of ice accretion, and then let the pilots decide when to use the 
autopilot. The commenter believes that prohibiting use of the autopilot 
when any ice is observed aft of the protected surfaces of the wing is a 
rigid requirement that takes away a valuable aid to the flight crew 
when it may be needed most. Raytheon states that there is no evidence 
that the autopilots on Beech aircraft would mask an icing related 
control problem. The commenter points out that tests on those aircraft 
disclosed no icing related control problem to mask. The commenter adds 
that trying to anticipate every situation with an absolute prohibition 
may lead to other unsafe conditions.
    The FAA does not concur that the autopilot limitation should be 
modified or removed from the AD's for any of the affected airplanes. 
The limited amount of time the pilot is using manual controls instead 
of the autopilot would not result in an unsafe condition. In normal 
operational environments and conditions, the autopilot is a valuable 
aid that reduces the workload of the flight crew. However, under 
abnormal conditions (ice aft of the protected surfaces, unusual lateral 
trim, or autopilot trim warnings), the autopilot will mask the build-up 
of large or unusual control forces in one or more axes. Therefore, for 
the short period of time necessary to exit severe icing conditions, the 
safest course of action would be manual pilot control. Even if an 
autopilot does not automatically disconnect, the pilot may choose to 
disconnect the autopilot and could then be faced unexpectedly with 
unusual control forces. These reasons also still hold true with 
airplanes that have been flight tested with the ice shapes.
    Since the issuance of the proposed rules, the FAA has re-examined 
the autopilot limitation specified in paragraph (a)(1) of the 
proposals. The FAA recognizes that clarification is necessary with 
regard to its intent concerning that limitation. That limitation, as 
specified in the proposals, states that use of the autopilot is 
prohibited when any ice is observed forming aft of the protected 
surfaces of the wing, or when unusual lateral trim requirements or 
autopilot trim warnings are encountered. However, the FAA's intent 
concerning that limitation is that the autopilot be disconnected when 
the flight crew observes any of the visual cues identified in paragraph 
(a)(1) of the AD's. The need to disconnect the autopilot arises when an 
amount of ice accumulates that indicates the limits of the ice 
protection equipment have been exceeded, regardless of the means by 
which the flight crew becomes aware of the accumulation of ice.
    Additionally, the FAA acknowledges that the autopilot limitation, 
as proposed, could be misinterpreted to mean that the autopilot must be 
disengaged when unusual lateral trim or autopilot trim warnings are 
encountered, regardless of whether the airplane is in icing conditions. 
However, the FAA only intended that the autopilot limitation apply 
while the airplane is in icing conditions.
    In light of this, the FAA has determined that the autopilot 
limitation contained in paragraph (a)(1) of the final rules must be 
revised. The FAA has changed that limitation to read as follows: 
``Since the autopilot may mask tactile cues that indicate adverse 
changes in handling characteristics, use of the autopilot is prohibited 
when any of the visual cues specified above exist, or when unusual 
lateral trim requirements or autopilot trim warnings are encountered 
while the airplane is in icing conditions.'' (This wording is slightly 
different in the final rule for Aerospatiale airplanes because only one 
visual cue is provided.) This revision more accurately reflects the 
FAA's intent and is, therefore, a logical outgrowth of the proposed 
rules.

Comment 46. Request To Insert Procedures in Limitations or Abnormal 
Procedures Section of AFM

    One commenter suggests that operations in icing conditions that 
exceed the capability of the airplane should be described in the 
Limitations or Abnormal Procedures Section of the AFM, rather than in 
the Normal Procedures Section, as specified in paragraph (a)(2) of the 
proposals.
    The FAA concurs partially. The FAA agrees that the Abnormal 
Procedures Section may be an appropriate location for the procedures 
for exiting severe icing conditions. However, the FAA does not agree 
that such operational procedures should appear in the Limitations 
Section of the AFM since such procedures are not limitations. 
Additionally, upon further review, the FAA finds that AFM's may have 
neither an Abnormal Procedures nor a Normal Procedures Section. 
Consequently, to provide operators with flexibility as to where the 
procedures specified in paragraph (a)(2) should be incorporated in the 
AFM, that paragraph has been revised to require that the ``Procedures'' 
Section of the AFM be revised. This means that the procedures may be 
inserted in the ``Normal Procedures,'' ``Abnormal Procedures,'' or 
other ``Procedures'' Section of the AFM, as appropriate.

Comment 47. Request To Remove Duplicate Visual Cues

    Two commenters indicate that certain visual cues specified in 
paragraph (a)(2) of the proposals are duplicated in the ``Warning'' 
that is also contained in that paragraph. One commenter states that the 
duplication of text reduces the impact of the message. Another 
commenter questions whether the visual cues and procedures for exiting 
the icing environment are intended to be part of the AFM material. The 
FAA infers from these remarks that the commenters request that 
duplicate text be removed.
    Transport Canada Aviation requests that the ``Warning'' be removed 
because indications of the possible hazard are progressive and may not 
necessarily require immediate action from the pilot. The commenter 
suggests that renaming this as a ``Caution'' may be more appropriate.
    The FAA concurs partially. The FAA agrees that duplicate text 
should be removed from the ``Warning'' section that appeared in the 
proposals. The FAA finds that only one unique instruction appears in 
the ``Warning'' in paragraph (a)(2) of the proposals: ``If the flaps 
are extended, do not retract them until the airframe is clear of ice.'' 
Therefore, the FAA has added that instruction to the procedures for 
exiting the severe icing environment in paragraph (a)(2) of the AD's. 
The remainder of the ``Warning'' section that appeared in the proposals 
has been removed from the final rules.

[[Page 20662]]

Comment 48. Request for Revision to Instruction for Flaps Extension

    Saab requests that the FAA revise an instruction contained in the 
procedures for exiting the freezing rain/freezing drizzle environment 
in paragraph (a)(2) of the proposals. That instruction indicates to 
``Avoid extending flaps during extended operation in icing conditions * 
* *.'' Saab suggests the following: ``Do not extend flaps when holding 
in conditions where ice is accreting on the airframe.'' Further, the 
commenter asks that this instruction be inserted as a ``caution'' in 
the Limitations Section of the AFM, rather than into the Normal 
Procedures Section, as specified in the proposed rule. Saab believes 
that it is imperative that the flaps not be extended in such cases. 
Inserting the instruction into the Limitations Section, rather than the 
Normal Procedures Section, would add strength to the requirement.
    Another commenter states that this same instruction appears to be 
in conflict with previously approved AFM revisions which state, 
``Sustained flight in icing conditions is prohibited with flaps 
extended.'' However, the commenter does not provide a suggestion for 
rewording this instruction.
    The FAA concurs that the procedures related to extension of the 
flaps can be reworded somewhat. For clarification purposes, the FAA has 
replaced the word ``avoid'' with ``do not'' in that procedure in 
paragraph (a)(2) of the final rules. This revision eliminates the 
conflict discussed by the second commenter. However, the FAA does not 
agree that revising the remainder of the instruction, as suggested by 
Saab, provides any additional clarification.
    The FAA agrees that inserting the revised wording in the 
Limitations Section of the AFM, rather than in the Normal Procedures 
Section, would be acceptable; however, this would expand the scope of 
the originally proposed rules and would necessitate reopening the 
comment period to provide additional opportunity for public comment. In 
light of the time required to complete the rulemaking process in 
advance of the upcoming icing season and in consideration of the safety 
issues addressed by these final rules, the FAA finds that the AD's 
should be issued without additional delay. However, the FAA would 
consider a request for approval of an alternative method of compliance, 
in accordance with the provisions of this AD, to include this 
information in the Limitations Section of an operator's AFM.
    Transport Canada Aviation requests that this instruction be revised 
to read as follows: ``Do not extend flaps during operation in icing 
conditions, except for approach and landing. Operation with flaps 
extended will result in a reduced wing angle-of-attack with the 
possibility of ice forming on the upper surface further aft on the wing 
than normal, possibly aft of the protected area.''
    The FAA concurs partially. The FAA does not concur with the 
commenter's suggested rewording to limit use of the flaps in all 
operation in icing conditions except approach and landing. The wording 
proposed in the AD's would affect use of the flaps only during extended 
operation in icing conditions. The FAA finds that an amount of ice 
sufficient to cause control problems is more likely to accumulate 
during prolonged operations in icing conditions. Further, the FAA does 
not concur that the words ``operation of the flaps can result in a 
reduced angle-of-attack * * *'' should be changed to ``operation of the 
flaps will result in a reduced angle-of-attack * * *'' in this 
instruction. Operation with flaps extended does not always result in a 
reduced angle-of-attack. For instance, during extension of the flaps 
while the airplane is slowing, the angle-of-attack will increase.
    The FAA concurs with the suggestion to include the words ``the 
possibility of ice forming on the upper surface further aft * * * .'' 
The FAA acknowledges that under certain conditions the droplets will 
not impinge further aft with a reduced angle-of-attack. The final rules 
have been revised to add the words suggested by the commenter to the 
sixth instruction specified in the procedures for exiting the severe 
icing environment contained in paragraph (a)(2) of the AD's. That 
revised instruction reads as follows: ``Do not extend flaps . . . with 
the possibility of ice forming on the upper surface * * * .''

Comment 49. Requests To Revise ``Caution'' Paragraph

    One commenter asks that the heading, ``Caution,'' which appears in 
paragraph (a)(2) of the proposals, be renamed ``Warning'' because this 
section is intended to prevent loss of life or injury. Transport Canada 
Aviation requests that the ``Caution'' section be changed to a note. 
The commenter provides no justification.
    The FAA concurs partially. The FAA does not concur that the 
``Caution'' should be changed to a note because this section is 
intended to prevent loss of life or injury. In light of this, the FAA 
concurs with the commenter's request to rename the ``Caution'' section 
``Warning.'' The FAA finds that ``Warning'' is a stronger term and 
would be a more appropriate heading for the paragraph in question. 
Additionally, the FAA finds that the ``Warning'' provides advisory 
information that should precede the first limitation in paragraph 
(a)(1) of the AD's. Accordingly, the FAA has revised the heading 
``Caution'' to ``Warning'' in the final rules. In addition, the 
``Warning'' has been placed at the beginning of paragraph (a)(1) of the 
final rules. The FAA has determined that including this information in 
the Limitations Section of the AFM will not impose an additional burden 
on any operator, since it is informational only and does not 
necessitate providing an additional opportunity for public comment.
    Additionally, the commenter notes that an undefined term, 
``extreme,'' is used in a sentence in the ``Caution'' paragraph of the 
proposals, as follows: ``Flight in freezing rain, freezing drizzle, or 
mixed icing conditions (supercooled liquid water and ice crystals) may 
result in extreme ice build-up on protected surfaces * * * .'' The FAA 
infers from this remark that the commenter asks that the word 
``extreme'' be removed from the ``Caution'' paragraph.
    The FAA concurs. The FAA finds that removing the word ``extreme'' 
would not change the intent of the sentence and may eliminate 
confusion. The word ``extreme'' has been removed from this section of 
the final rule. In addition, for clarification purposes, the FAA has 
revised the first sentence of the proposed ``Caution'' from ``Severe 
icing comprises environmental conditions . . .'' to ``Severe icing may 
result from environmental conditions * * * .''

Comment 50. Request To Remove Visual Cues: Identification of Freezing 
Rain/Freezing Drizzle

    One commenter indicates that the cues provided in paragraph (a)(2) 
of the proposals for identifying freezing rain/freezing drizzle 
conditions are duplicated in material that appears in paragraph (a)(1) 
of the proposals. The FAA infers from this remark that the commenter 
requests that duplicative wording be removed from paragraph (a)(2) of 
the proposed rules.
    The FAA concurs. The FAA finds that the section entitled ``The 
following shall be used to identify freezing rain/freezing drizzle 
icing conditions'' is duplicated in material that appears in paragraph 
(a)(1), and does not enhance the effectiveness of the AD's. Therefore, 
that section has been removed from paragraph (a)(2) of the final rules 
for all airplanes other than Aerospatiale Model ATR-42 and ATR-72 
series airplanes.

[[Page 20663]]

    Paragraph (a)(1) of the proposals for Aerospatiale airplanes 
specified secondary indications for identifying possible freezing rain/
freezing drizzle conditions. The FAA recognizes that the flight crew 
could have interpreted that paragraph to mean that if the secondary 
indicators were observed, the airplane must be flown clear of the 
severe icing conditions. However, the FAA's intent is that the flight 
crew must immediately request priority handling to exit the icing 
conditions only when the visual cue (ice on the side window) specified 
in paragraph (a)(1) of the AD is observed.
    Accordingly, the FAA has deleted the secondary indications of 
possible severe icing conditions from paragraph (a)(1) of the final 
rule for Aerospatiale airplanes. In addition, the FAA has removed the 
visual cue (ice on the side window) from paragraph (a)(2) of the final 
rule. The FAA has retitled the section containing the secondary 
indications of possible severe icing as follows: ``The following may be 
used as secondary indications of severe icing conditions.'' Further, 
the last two secondary indicators contained in that section are 
specified in the final rule in a section titled: ``The following 
weather conditions may be conducive to severe in-flight icing.'' (This 
change is explained further in Comment 51 below.)

Comment 51. Request To Remove Visual Cues: Identification of Possible 
Freezing Rain/Freezing Drizzle

    One commenter states that the word ``may'' in the following title, 
which appears in paragraph (a)(2) of the proposals, is confusing: ``The 
following may be used to identify possible freezing rain/freezing 
drizzle conditions.'' The commenter indicates that AFM procedures 
should provide a clear sequence of steps that must be followed and that 
such procedures should be explicit; general advice, regardless of how 
prudent, should be published elsewhere. The FAA infers from this remark 
that the commenter asks that the cues that appear under this section be 
deleted.
    The FAA does not concur that this section should be removed. The 
cues provided for identification of possible severe icing conditions 
will alert the pilot to the possibility that unusual ice accretion may 
develop. The FAA finds that the level of detail provided in the final 
rules will increase the level of pilot awareness and, consequently, 
will increase the level of safety over that which exists currently. 
Therefore, the FAA has determined that it is appropriate to incorporate 
this section in the AFM.
    However, the FAA finds that clarification is necessary with regard 
to the title of this section. The FAA finds that operators may 
misinterpret that title, as proposed, to mean that this section 
contains visual cues that should be used to identify possible severe 
icing conditions prior to takeoff, dispatch, or release while the 
airplane is on the ground. Additionally, the FAA finds that confusion 
could result in differentiating between the weather conditions 
specified in this section and the visual cues provided in paragraph 
(a)(1) of the AD's. For clarification purposes, the FAA has revised the 
title of this section to read as follows: ``The following weather 
conditions may be conducive to severe in-flight icing.''

Comment 52. Request To Revise Air Temperature References

    Transport Canada Aviation states that ambient temperature is 
indicated as static air temperature (SAT), rather than outside air 
temperature (OAT), for de Havilland Model DHC-8 series airplanes. The 
FAA infers from this remark the commenter requests that the ambient 
temperature that appears in the weather conditions specified in 
paragraph (a)(2) of the proposals be expressed as SAT for those 
airplanes.
    The FAA does not concur. The FAA does not intend to specify which 
specific indicator in the cockpit a pilot should use to determine the 
ambient air temperature. The FAA intends that the pilot use whatever 
means necessary to determine ambient air temperature.
    However, since airplanes may have indicators other than OAT, the 
FAA has replaced the words ``outside air temperature'' with ``ambient 
air temperature'' in the weather conditions, and in the procedures for 
exiting the severe icing environment, specified in paragraph (a)(2) of 
these final rules to eliminate confusion concerning the need for a 
specific type of indicator.
    In addition, the FAA has re-examined the ambient temperature of +5 
degrees Celsius that is specified in paragraph (a)(2) of the proposals. 
The FAA has determined that this temperature is too high to be used as 
a reliable indication of whether severe icing conditions may exist 
during flight. The FAA finds that 0 degrees Celsius is a more 
appropriate indication. The FAA has revised paragraph (a)(2) of the 
final rules for all airplanes accordingly.

Comment 53. Request To Replace Reference to Droplets that Splash or 
Splatter

    JAL requests that the weather condition that pertains to ``droplets 
that splash or splatter'' be removed from paragraph (a)(2) of the 
proposals. JAL believes that this weather condition places too much 
emphasis on subjective judgment. JAL states that normal rain conditions 
will contain droplets that splash or splatter upon impact with the 
windshield. JAL indicates that information included in its existing AFM 
revisions, specified as follows, adequately addresses the issue: 
``Prolonged operation in altitude bands where temperatures are near 
freezing and heavy moisture is visible on the windscreen should be 
avoided.''
    The FAA does not concur that this weather condition should be 
removed from the AD's. This weather condition must be used in 
conjunction with the temperature specified as a means of identifying 
severe in-flight icing conditions. The weather condition also will 
alert the pilot to the possibility that unusual ice accretion may 
develop. The FAA finds that the AFM information submitted by JAL does 
not provide an equivalent alert to the pilot.

Comment 54. Request To Revise Procedures for Exiting Freezing Rain/
Freezing Drizzle

    JAL requests that the procedures for exiting freezing rain/freezing 
drizzle specified in paragraph (a)(2) of the proposals be restricted to 
essential instructions that the flight crew must follow. JAL contends 
that the procedures contained in the proposals are not written in the 
appropriate format for AFM procedures, but are more representative of 
advisory material. JAL also states that the current FAA-approved AFM 
procedures for exiting freezing rain/freezing drizzle already provide 
this essential information and conform to the existing style of the 
AFM's. Transport Canada Aviation requests that the first instruction in 
these procedures be revised to state only: ``Exit the freezing rain or 
freezing drizzle conditions immediately.'' The commenter also requests 
clarification of the terms ``extended exposure,'' as used in that 
instruction.
    The FAA concurs partially. The FAA has reviewed the procedures for 
exiting the severe icing environment and finds that two of the 
instructions contained in those procedures do not require the level of 
detail provided in the proposed rules. The FAA finds that the 
information concerning masking of control system forces is already

[[Page 20664]]

provided in the Limitations Section of the AFM. Therefore, the FAA has 
revised the third instruction of those procedures to read as follows: 
``Do not engage the autopilot.'' Additionally, the FAA has determined 
that the flight crew need not be provided with instructions for 
reducing the angle-of-attack because instructions such as this are 
considered to be basic airmanship. Accordingly, the FAA has revised the 
fifth instruction in the procedures for exiting the severe icing 
environment to specify only information that is essential for the 
flight crew. The revised instruction reads as follows: ``If an unusual 
roll response * * * reduce the angle-of-attack.'' The FAA finds that, 
for the remainder of the procedures for exiting, the additional level 
of details provided in the final rules will increase the level of 
understanding and, consequently, will increase the level of safety over 
that which exists currently. The FAA finds that these procedures are 
appropriate for insertion in the AFM's.
    Regarding the terms ``extended exposure,'' the intent of that 
instruction is to advise the flight crew that exiting the severe icing 
conditions will minimize the exposure to flight conditions outside 
those for which the airplane has been certificated. The FAA finds that 
remaining in such conditions for a prolonged period may result in 
accumulating an amount of ice sufficient to cause control problems. The 
phrase ``to avoid extended exposure'' is only intended to explain to 
the flight crew why severe icing conditions should be exited 
immediately.
    Raytheon questions the necessity to tell a commercial pilot not to 
make any abrupt or excessive maneuvers if the aircraft is in the 
position of having control difficulties. This instruction appears under 
the heading ``Procedures for exiting the freezing rain/freezing drizzle 
environment,'' which appears in paragraph (a)(2) of the proposals. The 
commenter contends that this is a training issue and is not appropriate 
for AFM procedures. The FAA infers from the commenter's remark that the 
commenter requests that these instructions be eliminated from the 
proposed rules.
    The FAA does not concur. The FAA has determined that such 
instructions provide beneficial guidance to the flight crew, which will 
enhance the safety of the aircraft.
    Saab requests that the FAA revise one of the instructions specified 
in the procedures for exiting freezing rain/freezing drizzle specified 
in the proposals. The instruction states that if an unusual roll 
response or uncommanded control movement is observed, the angle-of-
attack should be reduced by increasing the airspeed or rolling the 
wings level (if in a turn), and applying additional power, if needed. 
Saab suggests that this instruction be revised to include the word 
``aileron'' in the reference to uncommanded control movement. Saab 
states further that in the case of wing ice beyond the protected 
surfaces, the application of power may be appropriate to increase 
airspeed/improve airflow. However, if ice has accrued on the wings 
beyond the protected surfaces, there is a possibility that there also 
is ice on the horizontal stabilizers. In this case, a sudden burst of 
power may be detrimental. An uncommanded pitch control movement is 
indicative of tail ice, which normally calls for a different action, 
both concerning power as well as the handling of flaps, if extended. 
Another commenter, Transport Canada Aviation, requests that the same 
instruction be revised to include the word ``lateral'' in reference to 
``uncommanded control movement,'' and to change the phrase ``or rolling 
wings level'' to ``and rolling wings level.''
    The FAA concurs partially. The FAA agrees that the correct 
procedures for reducing the angle-of-attack is to increase the airspeed 
and roll the wings level, if in a turn. However, as explained 
previously, this portion of the procedure has been removed from the 
final rules. The FAA does not agree that either ``lateral'' or 
``aileron'' should be used to specify the type of uncommanded control 
movement. The FAA finds that use of the term ``lateral'' may not be 
understood by the flight crew. The FAA finds that including the word 
``aileron'' may clarify which control surface is of concern; however, 
the FAA has determined that use of a more general term, ``roll'' will 
correctly specify the type of uncommanded control movement that is of 
concern. The FAA has revised the fifth instruction in the procedures 
for exiting the severe icing environment in paragraph (a)(2) of the 
final rules accordingly. The revised instruction reads as follows: ``If 
an unusual roll response or uncommanded roll control movement is 
observed, reduce the angle-of-attack.''
    In addition, the procedures for exiting the freezing rain/freezing 
drizzle environment contained in the proposals did not specify to use 
``a sudden burst of power'' when reducing the angle-of-attack. Rather, 
the proposed procedure indicates to apply additional power, if needed, 
to provide the desired flight path. However, as discussed previously, 
the FAA has removed this reference from the final rules. In addition, 
as explained previously, the FAA has revised the final rules to add the 
word ``roll'' to describe the type of uncommanded control movement. 
This revised wording addresses Saab's concern regarding increasing 
power for a pitch anomaly.
    Saab also notes that this instruction recommends a reduction in the 
angle-of-attack and application of power, if needed. However, the next 
instruction of the procedures indicates that reducing the angle-of-
attack may cause ice to build up beyond the protected areas of the 
wing. Saab concludes that there is a conflict in that the proposed AD 
would require that the angle-of-attack not be reduced or ice will 
collect beyond the protected surfaces; however, the angle-of-attack 
must be reduced if there is an unusual roll response or uncommanded 
control movement.
    The FAA does not concur with the commenter's contention that there 
is a conflict in the AD's. Reducing the angle-of-attack by increasing 
airspeed or rolling the wings level (if in a turn), and applying 
additional power, if needed, is a procedure used to exit severe icing 
conditions following an unusual roll response or uncommanded roll 
control movement; whereas the instruction that involves not extending 
the flaps during extended operation in icing conditions is intended to 
prevent ice build-up beyond the unprotected surfaces.
    Raytheon asks for removal of the instruction to reduce the angle-
of-attack and apply additional power, if needed, in response to an 
unusual roll response or uncommanded control movement. The commenter 
states that these are normal instructions with respect to wing stall 
and are inappropriate for inclusion in an AFM.
    The FAA concurs partially. There may not be a stall warning 
associated with uncommanded control movements in the case of encounters 
with severe icing conditions. Since this is not a ``normal'' stall, the 
flight crew may not recognize that normal stall recovery procedures 
should be used. However, as stated previously, the instruction 
referenced by the commenter has been deleted, in part, from the final 
rules.
    Raytheon also states that it is not appropriate to require contact 
with Air Traffic Control as part of an AFM procedure since this is 
already addressed in the Aeronautical Information Manual and in section 
91.183 of the Federal Aviation Regulations (14 CFR 91.183). The FAA 
infers from this statement that the commenter requests that the 
instruction to contact Air Traffic Control should be removed from the 
procedures for exiting severe icing conditions.

[[Page 20665]]

    The FAA does not concur. The FAA is aware that this instruction is 
contained in the references provided by the commenter. However, the FAA 
finds that the importance of timely dissemination of this instruction 
warrants its inclusion in the final rules. Inclusion of instructions of 
this type is not without precedent; for example, similar information 
also is specified in certain AFM's where the forward look windshear 
system is addressed.

Comment 55. Request To Revise Procedures for Exiting the Severe Icing 
Environment: Include Airplane-Specific Instructions

    One commenter suggests that any action that might be necessary to 
optimize aircraft performance and control in conditions of exceptional 
icing, and exit from those conditions, should be determined separately 
with each manufacturer; such procedures should be contained in the AFM 
for each airplane model. The FAA infers from this remark that the 
commenter requests that the FAA revise the procedures for exiting the 
severe icing environment in each final rule to include airplane-
specific instructions.
    The FAA agrees that procedures obtained from each individual 
manufacturer should be considered and included in the final rules, if 
appropriate. All manufacturers have been provided with an opportunity 
to submit such procedures in response to the proposed rules. Some 
manufacturers requested changes to the final rules. The FAA has revised 
the final rules for those requests that were substantiated adequately. 
Following issuance of the final rules, the FAA would consider a request 
to include additional changes to the AFM revisions, in accordance with 
the provisions of these AD's, provided that adequate justification is 
presented to support such a request.

Comment 56. Revision of Procedures for Exiting the Severe Icing 
Environment

    The FAA has re-examined the section titled ``Procedures for exiting 
the severe icing environment'' in paragraph (a)(2) of the proposals. As 
proposed, that section states that if the visual cues used for 
identifying ``possible'' freezing rain or freezing drizzle conditions 
are observed, the flight crew should follow the procedures specified 
for exiting those conditions. The FAA did not intend that the flight 
crew use the procedures for exiting the severe icing environment when 
the weather conditions specified in paragraph (a)(2) of these AD's are 
observed. The FAA's intent is that the flight crew use those procedures 
only when the visual cues identified in the Limitations Section of the 
AFM are observed.
    In order to eliminate any confusion, the FAA has revised the last 
sentence of the first paragraph in the procedures for exiting the 
severe icing environment. The FAA has removed the word ``possible'' 
from that sentence, and has added clarification that the visual cues 
are specified in the Limitations Section of the AFM. The revised 
sentence reads as follows: ``If the visual cues specified in the 
Limitations Section of the AFM for identifying severe icing conditions 
are observed, accomplish the following.'' (Operators should note that, 
for Aerospatiale airplanes, the final rule specifies only one visual 
cue, which involves ice on the side window.)

Comment 57. Request To Revise Cost Estimate

    Transport Canada requests that the FAA provide an operational cost 
estimate in the proposed AD's.
    The FAA acknowledges the concern of the commenter. The FAA 
recognizes that, in accomplishing the requirements of any AD, operators 
may incur other costs in addition to the ``direct'' costs that are 
reflected in the cost analysis presented in the AD preamble. However, 
the cost analysis in AD rulemaking actions typically only includes such 
direct costs. In the case of these AD's, for example, the requirements 
are to revise the AFM to include certain information. How operators 
actually ``implement'' that information thereafter (once it is placed 
in the AFM) may vary greatly among them.
    Further, because AD's require specific actions to address specific 
unsafe conditions, they appear to impose costs that would not otherwise 
be borne by operators. However, because of the general obligation of 
operators to maintain and operate aircraft in an airworthy condition, 
this appearance is deceptive. Attributing those costs solely to the 
issuance of this AD is unrealistic because, in the interest of 
maintaining and operating safe aircraft, prudent operators would 
accomplish the required actions even if they were not required to do so 
by the AD. In any case, the FAA has determined that direct and 
incidental costs are still outweighed by the safety benefits of the AD.
    The FAA points out that it is not required to do a full cost-
benefit analysis for each AD. AD's were explicitly exempted from the 
Office of Management and Budget (OMB) coordination process described in 
Section 6 of that Executive Order. As a matter of law, in order to be 
airworthy, an aircraft must conform to its type design and be in a 
condition for safe operation. The type design is approved only after 
the FAA makes a determination that it complies with all applicable 
airworthiness requirements. In adopting and maintaining those 
requirements, the FAA has already made the determination that they 
establish a level of safety that is cost-beneficial. When the FAA later 
makes a finding of an unsafe condition in an aircraft and issues an AD, 
it means that the original cost beneficial level of safety is no longer 
being achieved and that the required actions are necessary to restore 
that level of safety. Because this level of safety has already been 
determined to be cost beneficial, and because the AD does not add an 
additional regulatory requirement that increases the level of safety 
beyond what has been established by the type design, a full cost-
benefit analysis for each AD would be redundant and unnecessary.

Comment 58. Requests To Delay Issuance of the Final Rules

    Three commenters request that the FAA extend the comment period for 
the proposed rules by 90 days. Each of the commenters request the 
extension in order to complete a comprehensive analysis of this issue. 
The commenters state their involvement in focusing on ``* * * other 
recent rulemaking activity, including the Commuter Rule, flight 
crewmember training requirements, and proposed rules covering flight 
crew flight, duty and test requirements * * *'' as a reason that did 
not allow complete analysis of the proposed AD's.
    One commenter requests that implementation of the AD's be deferred 
until further discussion with industry has been undertaken.
    The FAA has reviewed these requests and, in consideration of the 
importance and need for dissemination of this important information to 
the aviation community, does not concur that the comment period should 
be extended or issuance of the final rules be deferred until a later 
date. Issuing the final rules will ensure that the information is 
available, understood, and implemented by the aviation community before 
the next icing season. For these reasons, the FAA has determined that 
it is imperative that the information and actions contained in these 
final rules be incorporated into the operators' AFM's immediately.

Conclusion

    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the

[[Page 20666]]

adoption of the rule with the changes previously described. The FAA has 
determined that these changes will neither increase the economic burden 
on any operator nor increase the scope of the AD.

Cost Impact

    The FAA estimates that 158 Aerospatiale Model ATR-42 and ATR-72 
series airplanes of U.S. registry will be affected by this AD, that it 
will take approximately 1 work hour per airplane to accomplish the 
required actions, and that the average labor rate is $60 per work hour. 
Based on these figures, the cost impact of the AD on U.S. operators is 
estimated to be $9,480, or $60 per airplane.
    For Model ATR-42 series airplanes, Modification 4216 (or 4222), as 
required in this AD, will take approximately 52 work hours per airplane 
to accomplish, at an average labor rate of $60 per work hour. Required 
parts will be supplied by the manufacturer at no cost to operators. 
Based on these figures, the cost impact on U.S. operators for this 
modification is estimated to be $492,960, or $3,120 per airplane.
    For Model ATR-72 series airplanes, Modification 4215 (or 4221), as 
required in this AD, will take approximately 96 work hours per airplane 
to accomplish. Required parts for this modification will be supplied by 
the manufacturer at no cost to operators. Modification 4213, as 
required in this AD, would take approximately 4 work hours to 
accomplish. Required parts will cost approximately $200 per airplane. 
The average labor rate for accomplishment of both modifications is $60 
per work hour. Based on these figures, the cost impact on U.S. 
operators for these modifications is estimated to be $979,600, or 
$6,200 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the requirements of this 
AD action, and that no operator would accomplish those actions in the 
future if this AD were not adopted.
    In addition, the FAA recognizes that this AD may impose operational 
costs. However, those costs are incalculable because the frequency of 
occurrence of the specified conditions and the associated additional 
flight time are indeterminable. Nevertheless, because of the severity 
of the unsafe condition addressed, the FAA has determined that 
continued operational safety necessitates the imposition of these 
costs.

Regulatory Impact

    The regulations adopted herein will not have substantial direct 
effects 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. Therefore, in 
accordance with Executive Order 12612, it is determined that this final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act. A final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends part 39 of 
the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 USC 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-9152 (60 FR 
9616, February 21, 1995), and by adding a new airworthiness directive 
(AD), amendment 39-9604, to read as follows:

96-09-28  Aerospatiale: Amendment 39-9604. Docket 95-NM-146-AD. 
Supersedes AD 95-02-51, Amendment 39-9152.

    Applicability: All Model ATR-42 and ATR-72 series airplanes, 
certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (d) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To minimize the potential hazards associated with operating the 
airplane in severe icing conditions by providing more clearly 
defined procedures and limitations associated with such conditions, 
accomplish the following:
    (a) Within 30 days after the effective date of this AD, 
accomplish the requirements of paragraphs (a)(1) and (a)(2) of this 
AD.

    Note 2: Operators must initiate action to notify and ensure that 
flight crewmembers are apprised of this change.

    (1) Revise the FAA-approved Airplane Flight Manual (AFM) by 
incorporating the following into the Limitations Section of the AFM. 
This may be accomplished by inserting a copy of this AD in the AFM.

``WARNING

    Severe icing may result from environmental conditions outside of 
those for which the airplane is certificated. Flight in freezing 
rain, freezing drizzle, or mixed icing conditions (supercooled 
liquid water and ice crystals) may result in ice build-up on 
protected surfaces exceeding the capability of the ice protection 
system, or may result in ice forming aft of the protected surfaces. 
This ice may not be shed using the ice protection systems, and may 
seriously degrade the performance and controllability of the 
airplane.
     During flight, severe icing conditions that exceed 
those for which the airplane is certificated shall be determined by 
the following visual cue. If the following visual cue exists, 
immediately request priority handling from Air Traffic Control to 
facilitate a route or an altitude change to exit the icing 
conditions.

--Severe icing is characterized by ice covering all or a substantial 
part of the unheated portion of either forward side window, possibly 
associated with water splashing and streaming on the windshield.

     Since the autopilot may mask tactile cues that indicate 
adverse changes in handling characteristics, use of the autopilot is 
prohibited when the visual cue specified above exists, or when 
unusual lateral trim requirements or autopilot trim warnings are 
encountered while the airplane is in icing conditions.
     All icing detection lights must be operative prior to 
flight into icing conditions at night. [NOTE: This supersedes any 
relief provided by the Master Minimum Equipment List (MMEL).]''
     The ice detector must be operative for flight into 
icing conditions.

[[Page 20667]]

    (2) Revise the FAA-approved AFM by incorporating the following 
into the Procedures Section of the AFM. This may be accomplished by 
inserting a copy of this AD in the AFM.

``THE FOLLOWING MAY BE USED AS SECONDARY INDICATIONS OF SEVERE ICING 
CONDITIONS:

     Unusually extensive ice accreted on the airframe in 
areas not normally observed to collect ice.
     Accumulation of ice on the lower surface of the wing 
aft of the protected area.
     Accumulation of ice on the propeller spinner farther 
aft than normally observed.

THE FOLLOWING WEATHER CONDITIONS MAY BE CONDUCIVE TO SEVERE IN-FLIGHT 
ICING:

     Visible rain at temperatures below 0 degrees Celsius 
ambient air temperature.
     Droplets that splash or splatter on impact at 
temperatures below 0 degrees Celsius ambient air temperature.

PROCEDURES FOR EXITING THE SEVERE ICING ENVIRONMENT:

    These procedures are applicable to all flight phases from 
takeoff to landing. Monitor the ambient air temperature. While 
severe icing may form at temperatures as cold as -18 degrees 
Celsius, increased vigilance is warranted at temperatures around 
freezing with visible moisture present. If the visual cue specified 
in the Limitations Section of the AFM for identifying severe icing 
conditions is observed, accomplish the following:
     Immediately request priority handling from Air Traffic 
Control to facilitate a route or an altitude change to exit the 
severe icing conditions in order to avoid extended exposure to 
flight conditions more severe than those for which the airplane has 
been certificated.
     Avoid abrupt and excessive maneuvering that may 
exacerbate control difficulties.
     Do not engage the autopilot.
     If the autopilot is engaged, hold the control wheel 
firmly and disengage the autopilot.
     If an unusual roll response or uncommanded roll control 
movement is observed, reduce the angle-of-attack.
     Do not extend flaps during extended operation in icing 
conditions. Operation with flaps extended can result in a reduced 
wing angle-of-attack, with the possibility of ice forming on the 
upper surface further aft on the wing than normal, possibly aft of 
the protected area.
     If the flaps are extended, do not retract them until 
the airframe is clear of ice.
     Report these weather conditions to Air Traffic 
Control.'' -
    (b) Within 6 months after the effective date of this AD, modify 
the deicing boots on the leading edges of the wing by accomplishing 
either paragraph (b)(1) or (b)(2) of this AD, as applicable. -
    (1) For Model ATR-42 series airplanes: Accomplish Aerospatiale 
Modification 4216 (during retrofit) or 4222 (during production), as 
applicable. Modification 4216 shall be accomplished in accordance 
with Aerospatiale Service Bulletin ATR42-30-0059, Revision 1, dated 
April 10, 1995; and ATR42-57-0043, Revision 1, dated April 10, 1995. 
Modification 4222 shall be accomplished in accordance with 
Aerospatiale Service Bulletin ATR42-57-0043, Revision 1, dated April 
10, 1995. -
    (2) For Model ATR-72 series airplanes: Accomplish Aerospatiale 
Modification 4215 (during retrofit) or 4221 (during production), as 
applicable. Modification 4215 shall be accomplished in accordance 
with Aerospatiale Service Bulletin ATR72-30-1023, Revision 1, dated 
April 10, 1995; ATR72-57-1015, Revision 1, dated April 10, 1995; and 
ATR72-57-1016, Revision 1, dated April 10, 1995. Modification 4221 
shall be accomplished in accordance with Aerospatiale Service 
Bulletin ATR72-57-1015, Revision 1, dated April 10, 1995; and ATR72-
57-1016, Revision 1, dated April 10, 1995. -
    (c) For Model ATR-72 series airplanes: Within 6 months after the 
effective date of this AD, install Aerospatiale Modification 4213, 
``Flaps Extension Inhibition above VFE 15 deg.,'' in accordance with 
Aerospatiale Service Bulletin ATR72-27-1039, dated January 12, 1995. 
-
    (d) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Standardization Branch, ANM-113, 
FAA, Transport Airplane Directorate. Operators shall submit their 
requests through an appropriate FAA Principal Operations Inspector, 
who may add comments and then send it to the Manager, 
Standardization Branch, ANM-113.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Standardization Branch, ANM-113.

     -(e) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished. -
    (f) The modifications shall be done in accordance with the 
following Aerospatiale service bulletins, which contain the 
specified effective pages:

----------------------------------------------------------------------------------------------------------------
 Service bulletin referenced                                    Revision level shown                            
           and date                        Page No.                    on page            Date shown on page    
----------------------------------------------------------------------------------------------------------------
ATR42-30-0059, Revision 1,     1-3, 12-17, 31, 32               1-                    April 10, 1995.           
 April 10, 1995.                                                                                                
                               4-11, 18-30, 33-36               Original              March 20, 1995.           
ATR42-57-0043, Revision 1,     1-4, 6, 8                        1-                    April 10, 1995.           
 April 10, 1995.                                                                                                
                               5, 7, 9-18                       Original              March 20, 1995.           
ATR72-30-1023, Revision 1,     1, 2, 12-17, 33, 34-             1-                    April 10, 1995.           
 April 10, 1995.                                                                                                
  -                            3-11, 18-32, 35-38-              Original-             March 20, 1995.           
ATR72-57-1015, Revision 1,     1, 2, 5, 6, 8, 11, 15-           1-                    April 10, 1995.           
 April 10, 1995.                                                                                                
  -                            3, 4, 7, 9, 10, 12-14, 16        Original              March 20, 1995.           
ATR72-57-1016, Revision 1,     1, 2, 5, 6, 8, 11, 15-           1-                    April 10, 1995.           
 April 10, 1995.                                                                                                
                               3, 4, 7, 9, 10, 12-14-           Original-             March 20, 1995.           
----------------------------------------------------------------------------------------------------------------

    The incorporation by reference of these documents was approved 
by the Director of the Federal Register in accordance with 5 U.S.C. 
552(a) and 1 CFR part 51. The installation shall be done in 
accordance with Aerospatiale Service Bulletin ATR72-27-1039, dated 
January 12, 1995. The incorporation by reference of these documents 
was approved previously by the Director of the Federal Register, in 
accordance with 5 U.S.C. 552(a) and 1 CFR part 51, as of March 8, 
1995 (60 FR 9616, February 21, 1995). Copies may be obtained from 
Aerospatiale, 316 Route de Bayonne, 31060 Toulouse, Cedex 03, 
France. Copies may be inspected at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the 
Office of the Federal Register, 800 North Capitol Street, NW., suite 
700, Washington, DC.
    (g) This amendment becomes effective on June 11, 1996.

    Issued in Renton, Washington, on April 24, 1996.
Ronald T. Wojnar,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
    Certified to be a true copy of the original.
Lori Aliment,
Certifying Officer.
[FR Doc. 96-10744 Filed 5-1-96; 3:25 pm]
BILLING CODE 4910-13-P