[Federal Register Volume 64, Number 195 (Friday, October 8, 1999)]
[Proposed Rules]
[Pages 54801-54804]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-26398]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-CE-39-AD]
RIN 2120-AA64


Airworthiness Directives; LET, a.s. Model L-420 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes to adopt a new airworthiness directive 
(AD) that would apply to all LET, a.s. (LET) Model L-420 airplanes. The 
proposed AD would require revising the Airplane Flight Manual (AFM) to 
include requirements for activation of the airframe pneumatic deicing 
boots. The proposed AD is the result of reports of in-flight incidents 
and an accident that occurred in icing conditions where the airframe 
pneumatic deicing boots were not activated. The actions specified by 
the proposed AD are intended to assure that flightcrews activate the 
pneumatic wing and tail deicing boots at the first signs of ice 
accumulation. This action will prevent reduced controllability of the 
aircraft due to adverse aerodynamic effects of ice adhering to the 
airplane prior to the first deicing cycle.

DATES: Comments must be received on or before December 1, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Central Region, Office of the Regional Counsel, 
Attention: Rules Docket No. 99-CE-39-AD, Room 1558, 601 E. 12th Street, 
Kansas City, Missouri 64106. Comments may be inspected at this location 
between 8 a.m. and 4 p.m., Monday through Friday, holidays excepted.

FOR FURTHER INFORMATION CONTACT: Mr. John P. Dow, Sr., Aerospace 
Engineer, FAA, Small Airplane Directorate, 1201 Walnut, suite 900, 
Kansas City, Missouri 64106; telephone: (816) 426-6932; facsimile: 
(816) 426-2169.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications should identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report that summarizes each FAA-public contact concerned 
with the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket No. 99-CE-39-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Central Region, Office of the Regional Counsel, Attention: 
Rules Docket No. 99-CE-39-AD, Room 1558, 601 E. 12th Street, Kansas 
City, Missouri 64106.

Discussion

    On January 9, 1997, an Empresa Brazileira de Aeronautica, S.A. 
(EMBRAER) Model EMB-120RT series airplane was involved in an 
uncommanded roll excursion and consequent rapid descent that resulted 
in an accident near Monroe, Michigan. The post-accident investigation 
conducted by the National Transportation Safety Board (NTSB) concluded 
that the airplane had accumulated a thin, rough layer of ice on its 
lifting surfaces. That accumulation of ice, in combination with the 
slowing of the airplane to an airspeed inappropriate for the icing 
conditions in which the airplane was flying, resulted in loss of 
control that was not corrected before the airplane impacted the ground. 
The NTSB also concluded that the flight crew did not activate the wing 
and tail pneumatic deicing boots. An NTSB recommendation related to 
this accident requested that the FAA mandate that pneumatic deicing 
boots be turned on as soon as the airplane enters icing conditions.
    The FAA has reviewed the icing-related incident history of certain 
airplanes, and has determined that icing incidents may have occurred 
because pneumatic deicing boots were not activated at the first 
evidence of ice accretion. As a result, the handling qualities or the 
controllability of the airplane may have been reduced due to the 
accumulated ice. That factor was present in the accident discussed 
previously and, as such, constitutes an unsafe condition.

Request for Information

    On October 1, 1998, the FAA sent letters to certain manufacturers 
of airplanes certified in accordance with part 25 of the Federal 
Aviation Regulations (14 CFR part 25). The letters requested certain 
icing system design information and operational procedures applicable 
to their airplanes concerning flight during icing conditions. The 
letters also requested that manufacturers provide data showing that the 
aircraft has safe operating characteristics with ice accreted on the 
protected surfaces (boots). The manufacturers were asked to provide 
data using the following assumptions: The most adverse ice accumulation 
possible during operation in the icing envelope specified in part 25, 
Appendix C of the Federal Aviation Regulations (14 CFR part 25), and 
that recommended procedures for deicing boot operation were used. 
Additionally, the manufacturers were asked to provide information 
related to operation of the autopilot during icing conditions, and for 
information related to appropriate operating speeds for icing 
operations.
    No information received, as a result of that request, has caused 
the FAA to

[[Page 54802]]

reconsider the previous conclusion that an unsafe condition may exist.

Public Meeting

    Subsequent to the collection of those design and operational data, 
the FAA held an international conference on ``Inflight Operations in 
Icing Conditions'', in Washington, DC, on February 2-4, 1999. The 
purpose of the conference was to discuss the status of the FAA Icing 
Plan and other related efforts. Additionally, the conference provided a 
forum for representatives of industry to express their viewpoints on 
current information related to activation of deicing boots, minimum 
airspeeds, autopilot operation in icing conditions, flightcrew 
information needs, and flightcrew training. Certain information 
presented at that meeting is discussed in this proposed rule in the 
following section.

Delayed Activation of Pneumatic Deicing Boots

    In accordance with manufacturer instructions and FAA-approved 
airplane flight manual (AFM) procedures, the flightcrews of most 
airplanes equipped with pneumatic deicing boots delay the initial 
activation of the boots until a certain quantity of ice has accumulated 
on the protected surfaces (boots). Some crews routinely wait for \1/4\ 
to \1/2\ inch of ice to accumulate, and at least one airplane type is 
routinely flown with up to 1\1/2\ inches of ice on the protected 
surfaces before the initial activation of the deicing boots.

Ice Bridging

    In the past, concern about ``ice bridging'' on early pneumatic 
deicing boot designs resulted in the common practice of delaying 
activation of ice protection. Ice bridging of pneumatic deicing boots 
occurred when a thin layer of ice is sufficiently plastic to deform to 
the shape of the inflated deicing boot tube without being fractured and 
shed during the ensuing tube deflation. As the deformed ice hardens and 
accretes additional ice, the deicing boot becomes ineffective in 
shedding the ``sheath'' of ice. However, ice accumulation resulting 
from delayed activation may pose an unsafe condition due to the 
resultant adverse aerodynamic effects on the airplane's performance or 
handling qualities.
    In November 1997, the FAA and the National Aeronautics and Space 
Administration (NASA) co-sponsored an international workshop on 
aircraft deicing boot ice bridging. The objective of the workshop was 
to provide an open forum for investigating the existence of deicing 
boot bridging and other concerns related to activating ice protection 
systems at the initial detection of inflight icing. Sixty-seven 
representatives from airframe and deicing boot manufacturers, various 
airlines, the pilot community, NASA, the National Transportation Safety 
Board, non-US civil aviation authorities, and the FAA participated. At 
the workshop no evidence was presented to substantiate that aircraft 
with modern deicing boot designs experience ice bridging. The general 
consensus of the workshop participants was that ice bridging is not a 
problem for modern pneumatic deicing boot designs due to the use of 
higher air supply pressures, faster boot inflation and deflation 
cycles, and smaller boot chambers. Icing wind tunnel and flight testing 
of these newer design features with automatic cycling have demonstrated 
successful shedding of ice when activated at the onset of ice 
accretion, with ice not shed on the initial deicing boot cycle 
continuing to increase in thickness and being shed during subsequent 
cycles.
    During the previously discussed November 1997 international 
workshop, the inability of flightcrews to accurately gauge wing and 
control surfaces ice accretion thickness before activating the deicing 
boots was recognized. Also, increased airplane drag resulting from ice 
accretion was recognized as a potential contributing cause of 
inadvertent airspeed loss that characterized most in-flight icing 
related accidents and incidents. Two airframe manufacturers, whose 
products comprise a substantial percentage of the turbopropeller 
transport fleet, reported that, because of these concerns they 
recommend activating the automatic airframe deicing system at first 
onset of airframe icing. Those manufacturers have received no reports 
of deicing boot ice bridging events for these airplanes.
    The FAA considers that ice accumulation on protected surfaces due 
to delayed boot activation constitutes a potential safety concern. 
However, the FAA recognizes that not all airplanes may be equipped with 
``modern'' deicing boots (as that term is used in this NPRM). The FAA 
specifically invites the submission of comments and other data 
regarding the effects of this proposed AD on airplanes equipped with 
older pneumatic deicing boots, including arguments for the retention of 
existing activation delays for these older-style deicing boots.

Residual Ice

    During the February conference, the attendees agreed that the 
airplane is at risk while the airplane is accreting ice, and that the 
airplane must be adequately protected to ensure that no adverse 
handling and performance characteristics develop. An additional concern 
discussed at the conference was the possibility that early activation 
of the ice protection system might degrade the ice shedding 
effectiveness of the deicing boots, resulting in increased residual 
ice, i.e., there would be more ice fragments remaining on the deicing 
boots than would exist if a more substantial quantity of ice was 
allowed to form before the first ice shedding cycle. However, the FAA 
does not concur. No data has been provided that shows that the presence 
of residual ice following an earlier activation of the deicing boots is 
more hazardous than delaying cycling of the boots until the ice 
accretes to a larger, specific thickness. In fact, testing in icing 
conditions has shown that residual ice remaining on the boots after the 
initial boot cycle is removed during subsequent cycles.
    As reported during the November 1997 international workshop, 
manufacturers of a substantial percentage of the turbopropeller 
transport fleet have reported satisfactory in-flight icing operations 
of their products with recommended procedures to activate operation of 
the deicing boots in the automatic mode at the onset of airframe icing.
    Therefore, the FAA considers that the activation of pneumatic wing 
and tail deicing boots at the first signs of ice accumulation is 
warranted. The FAA specifically invites the submission of data to 
substantiate that operating the deicing boots at the first sign of ice 
accretions is more hazardous than delaying boot activation until a 
specific thickness of ice has accumulated.

Other Considerations

    The FAA recognizes that there may be some phases of flight during 
which use of the deicing boots may be inappropriate. For example, a 
deicing boot inflation cycle that begins immediately before or during 
the landing flare or the takeoff rotation may cause unexpected loss of 
lift or other adverse aerodynamic events. This proposed AD explicitly 
does not supersede procedures in the AFM that prohibit using deicing 
boots for certain phases of flight (e.g., during take-off, final 
approach, and landing).
    The FAA specifically invites the submission of comments and other 
data regarding adverse effects that may occur during specific phases of 
flight, including takeoff, final approach, or landing. Any recommended 
speed restrictions or other operational procedures that would be 
necessary in

[[Page 54803]]

order to mitigate any adverse aerodynamic effects of deicing boot 
inflation during critical phases of flight should be fully explained 
and documented.

The FAA's Determination

    The FAA is aware that, based on previous procedures provided to 
flightcrews of many airplanes equipped with deicing boots, a historical 
precedent has been set that permits waiting to activate the deicing 
equipment. In light of this information and based on reports received, 
the FAA considers that certain procedures should be included in the 
Limitations Section of the AFM for all LET Model L-420 airplanes to 
require immediate activation of the ice protection systems when any ice 
accumulation is detected on the airplane.
    This proposed action is one of a number of proposed AD's being 
issued on airplanes that have been determined to be subject to the same 
identified unsafe conditions. Currently proposed AD's for other 
airplanes that are equipped with pneumatic deicing boots address the 
following airplanes:

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                   Airplane models                         Docket No.
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Industrie Aeronautiche e Mecchaniche, Model P-180            99-CE-34-AD
 Airplanes...........................................
Pilatus Britten-Norman Ltd., BN-2T Series Airplanes..        99-CE-35-AD
Pilatus Aircraft Ltd., Models PC-12 and PC-12/45             99-CE-36-AD
 Airplanes...........................................
Partenavia Costruzioni Aeronauticas, S.p.A., Models          99-CE-37-AD
 AP68TP 300 ``Spartacus'' and AP68TP 600 ``Viator''
 Airplanes...........................................
Mitsubishi Heavy Industries, Ltd., MU-2B Series              99-CE-38-AD
 Airplanes...........................................
British Aerospace, Jetstream Models 3101 and 3201            99-CE-40-AD
 Airplanes...........................................
Harbin Aircraft Manufacturing Corp., Model Y12 IV            99-CE-41-AD
 airplanes...........................................
Empresa Brasileira de Aeronautica S.A. (Embraer),            99-CE-42-AD
 Models EMB-110P1 and EMB-110P2 Airplanes............
Dornier Luftfahrt GmbH, 228 Series Airplanes.........        99-CE-43-AD
Bombardier Inc., DHC-6 Series Airplanes..............        99-CE-44-AD
The Cessna Aircraft Company, 208 Series Airplanes....        99-CE-45-AD
Raytheon Aircraft Company, 90, 99, 100, 200, 300,            99-CE-46-AD
 1900, and 2000 Series Airplanes.....................
AeroSpace Technologies Of Australia Pty Ltd., Models         99-CE-47-AD
 N22B and N24A.......................................
Short Brothers & Harland Ltd., Models SC-7 Series 2          99-CE-48-AD
 and SC-7 Series 3 Airplanes.........................
The New Piper Aircraft, Inc., PA-31 Series Airplanes.        99-CE-49-AD
SOCATA--Groupe AEROSPATIALE, Model TBM 700 Airplanes.        99-CE-50-AD
Twin Commander Aircraft Corporation, 600 Series              99-CE-51-AD
 Airplanes...........................................
Fairchild Aircraft Corporation, SA226 and SA227              99-CE-52-AD
 Series Airplanes....................................
The Cessna Aircraft Company, Models 425 and 441              99-CE-53-AD
 Airplanes...........................................
Cessna Aircraft Company, Models 500, 550, and 560           99-NM-136-AD
 Airplanes...........................................
Sabreliner Corporation Models, 40, 60, 70, and 80           99-NM-137-AD
 Series Airplanes....................................
Gulfstream Aerospace, Model G-159 Series Airplanes...       99-NM-138-AD
McDonnell Douglas, Models DC-3 and DC-4 Series              99-NM-139-AD
 Airplanes...........................................
Mitsubishi Heavy Industries, Model YS-11 and YS-11A         99-NM-140-AD
 Series Airplanes....................................
Frakes Aviation Model G-73 (Mallard) and G-73T Series       99-NM-141-AD
 Airplanes...........................................
Lockheed, Models L-14 and L-18 Series Airplanes......       99-NM-142-AD
Fairchild Models F27 and FH227 Series Airplanes......       99-NM-143-AD
Aerospatiale Models ATR-42/ATR-72 Series Airplanes...       99-NM-144-AD
Jetstream Model BAe ATP Airplanes....................       99-NM-145-AD
Jetstream Model 4101 Airplanes.......................       99-NM-146-AD
British Aerospace Model HS 748 Series Airplanes......       99-NM-147-AD
Saab Model SF340A/SAAB 340B/SAAB 2000 Series                99-NM-148-AD
 Airplanes...........................................
CASA Model C-212/CN-235 Series Airplanes.............       99-NM-149-AD
Dornier Model 328-100 Series Airplanes...............       99-NM-150-AD
Lockheed Model 1329-23 and 1329-25 (Lockheed Jetstar)       99-NM-151-AD
 Series Airplanes....................................
de Havilland Model DHC-7/DHC-8 Series Airplanes......       99-NM-152-AD
Fokker Model F27 Mark 100/200/300/400/500/600/700/050       99-NM-153-AD
 Series Airplanes....................................
Short Brothers Model SD3-30/SD3-60/SD3-SHERPA Series        99-NM-154-AD
 Airplanes...........................................
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Explanation of the Provisions of the Proposed AD

    Since an unsafe condition has been identified that is likely to 
exist or develop in other LET Model L-420 airplanes of the same type 
design registered in the United States, the FAA is proposing AD action. 
The proposed AD would require revising the Limitations Section of the 
AFM to include requirements for activation of pneumatic deicing boots 
at the first indication of ice accumulation on the airplane.

Cost Impact

    The FAA estimates that 1 airplane in the U.S. registry would be 
affected by the proposed AD, that it would take approximately 1 
workhour per airplane to accomplish the proposed AFM revisions. 
Accomplishing the proposed AFM revision requirements of this NPRM may 
be performed by the owner/operator holding at least a private pilot 
certificate as authorized by Sec. 43.7 of the Federal Aviation 
Regulations (14 CFR 43.7), and must be entered into the aircraft 
records showing compliance with the proposed AD in accordance with 
section 43.9 of the Federal Aviation Regulations (14 CFR 43.9). The 
only cost impact of the proposed AD is the time it would take each 
owner/operator of the affected airplanes to insert the information into 
the AFM.

Regulatory Impact

    The regulations proposed herein would 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 
proposal would 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

[[Page 54804]]

Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, 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 copy of the draft 
regulatory evaluation prepared for this action has been placed in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
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 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding a new airworthiness directive 
(AD) to read as follows:

Let, A.S.: Docket No. 99-CE-39-AD.

    Applicability: Model L-420 airplanes, all serial numbers 
equipped with pneumatic deicing boots, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
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 in the body of this AD, unless 
already accomplished.
    To assure that flightcrews activate the wing and tail pneumatic 
deicing boots at the first signs of ice accumulation on the 
airplane, accomplish the following:
    (a) Within 10 days after the effective date of this AD: Revise 
the Limitations Section of the FAA-approved Airplane Flight Manual 
(AFM) to include the following requirements for activation of the 
ice protection systems. This may be accomplished by inserting a copy 
of this AD in the AFM.
    `` Except for certain phases of flight where the AFM 
specifies that deicing boots should not be used (e.g., take-off, 
final approach, and landing), compliance with the following is 
required.
     Wing and Tail Leading Edge Pneumatic Deicing Boot 
System, if installed, must be activated:

--At the first sign of ice formation anywhere on the aircraft, or 
upon annunciation from an ice detector system, whichever occurs 
first; and
--The system must either be continued to be operated in the 
automatic cycling mode, if available; or the system must be manually 
cycled as needed to minimize the ice accretions on the airframe.

     The wing and tail leading edge pneumatic deicing boot 
system may be deactivated only after leaving icing conditions and 
after the airplane is determined to be clear of ice.''
    (b) Incorporating the AFM revisions, as required by this AD, may 
be performed by the owner/operator holding at least a private pilot 
certificate as authorized by Sec. 43.7 of the Federal Aviation 
Regulations (14 CFR 43.7), and must be entered into the aircraft 
records showing compliance with this AD in accordance with Sec. 43.9 
of the Federal Aviation Regulations (14 CFR 43.9).
    (c) Special flight permits may be issued in accordance with 
Secs. 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.
    (d) An alternative method of compliance or adjustment of the 
compliance time that provides an equivalent level of safety may be 
approved by the Manager, Small Airplane Directorate, 1201 Walnut, 
suite 900, Kansas City, Missouri 64106. The request shall be 
forwarded through an appropriate FAA Maintenance Inspector, who may 
add comments and then send it to the Manager, Small Airplane 
Directorate.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Small Airplane Directorate.

    (e) Information related to this AD may be examined at the FAA, 
Central Region, Office of the Regional Counsel, Room 1558, 601 E. 
12th Street, Kansas City, Missouri 64106.

    Issued in Kansas City, Missouri, on October 4, 1999.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 99-26398 Filed 10-7-99; 8:45 am]
BILLING CODE 4910-13-U