[Federal Register Volume 64, Number 193 (Wednesday, October 6, 1999)]
[Proposed Rules]
[Pages 54239-54240]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-26086]



[[Page 54239]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-226-AD]
RIN 2120-AA64


Airworthiness Directives; Short Brothers Model SD3-60 SHERPA, 
SD3-SHERPA, SD3-30, and SD3-60 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to all Short Brothers Model SD3-60 
SHERPA, SD3-SHERPA, SD3-30, and SD3-60 series airplanes. This proposal 
would require replacement of the existing pneumatic de-icing boot 
pressure indicator switch with a newly designed switch. This proposal 
is prompted by an occurrence on a similar airplane model in which the 
pneumatic de-icing boot indication light may have provided the 
flightcrew with misleading information as to the proper functioning of 
the de-icing boots. The actions specified by the proposed AD are 
intended to prevent ice accumulation on the airplane leading edges, 
which could reduce controllability of the airplane.

DATES: Comments must be received by November 5, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-226-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except 
Federal holidays.
    Information concerning this proposal may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Norman B. Martenson, Manager, 
International Branch, ANM-116, FAA, Transport Airplane Directorate, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
227-2110; fax (425) 227-1149.

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 shall 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 summarizing 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 Number 99-NM-226-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, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 99-NM-226-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On December 26, 1989, a British Aerospace Jetstream Model BA-3101 
series airplane impacted the ground approximately 400 feet short of the 
runway while executing an instrument landing system (ILS) approach. The 
accident occurred at the Tri-Cities Airport, Pasco, Washington. The 
National Transportation Safety Board (NTSB) determined that the 
probable cause of the accident was the flightcrew's decision to 
continue an unstabilized ILS approach that led to a stall, most likely 
of the horizontal stabilizer, and loss of control at low altitude. 
Contributing to the stall and loss of control was the accumulation of 
leading edge ice, which degraded the aerodynamic performance of the 
airplane.
    One result of the NTSB investigation was the determination that the 
flight deck wing de-icing light illuminated at a lower pressure than 
the pressure required to fully inflate the de-icing boots. The 
premature illumination of the wing de-icing light was due to a failure 
within the wing de-icing boot system, which allowed sufficient air 
pressure to give the appearance of normal operation based on the de-
icing light, without actually inflating the boots sufficiently to 
remove ice.
    Based on an NTSB Safety Recommendation, the FAA reviewed the 
pneumatic de-icing boot system designs for airplanes operated under 
parts 121 and 135 of the Federal Aviation Regulations to ensure that 
the pneumatic pressure threshold at which each de-icing boot indication 
light is designed to illuminate is sufficient pressure for effective 
operation of the pneumatic de-icing boots. The FAA has determined that 
the flight deck pneumatic de-icing boot pressure indicator switch on 
all Short Brothers Model SD3-60 SHERPA, SD3-SHERPA, SD3-30, and SD3-60 
series airplanes may allow the flight deck indication light to 
illuminate at a lower pressure [10 pounds per square inch gage (psig)] 
than the pressure required to fully inflate the de-icing boots (15 
psig). This condition, if not corrected, could result in ice 
accumulation on the airplane leading edges, which could reduce 
controllability of the airplane.

FAA's Conclusions

    These airplane models are manufactured in the United Kingdom and 
are type certificated for operation in the United States under the 
provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 
21.29) and the applicable bilateral airworthiness agreement. The FAA 
has determined that AD action is necessary for products of this type 
design that are certificated for operation in the United States.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other airplanes of the same type design registered 
in the United States, the proposed AD would require that the existing 
pneumatic de-icing boot pressure indicator switch be replaced with a 
switch that activates the indicator light at 15 psig. The action would 
be required in accordance with a method approved by the FAA.

Cost Impact

    The FAA estimates that 89 airplanes of U.S. registry would be 
affected by this proposed AD. Since the manufacturer has not yet 
developed one specific modification commensurate with the requirements 
of this proposal, the FAA is unable at this time to provide specific 
information as to the number of work hours or cost of parts that would 
be

[[Page 54240]]

required to accomplish the proposed modification. As indicated earlier 
in this preamble, the FAA specifically invites the submission of 
comments and other data regarding the economic aspect of this proposal.

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 proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
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 is contained 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 the following new 
airworthiness directive:

Short Brothers PLC: Docket 99-NM-226-AD.

    Applicability: All Model SD3-60 SHERPA, SD3-SHERPA, SD3-30, and 
SD3-60 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 
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 (b) 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 prevent ice accumulation on the airplane leading edges, which 
could reduce controllability of the airplane, accomplish the 
following:

Modification

    (a) Within 1 year after the effective date of this AD, replace 
the flight deck pneumatic de-icing boot pressure indicator switch 
with a switch that activates the flight deck indicator light at 15 
pounds per square inch gage, in accordance with a method approved by 
the Manager, International Branch, ANM-116, FAA, Transport Airplane 
Directorate.

Alternative Methods of Compliance

    (b) 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, International Branch, ANM-116. 
Operators shall submit their requests through an appropriate FAA 
Principal Maintenance Inspector, who may add comments and then send 
it to the Manager, International Branch, ANM-116.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the International Branch, ANM-116.

Special Flight Permits

    (c) 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.

    Issued in Renton, Washington, on September 30, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-26086 Filed 10-5-99; 8:45 am]
BILLING CODE 4910-13-P