[Federal Register Volume 61, Number 166 (Monday, August 26, 1996)]
[Proposed Rules]
[Pages 43692-43694]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-21594]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-40-AD]
RIN 2120-AA64


Airworthiness Directives; British Aerospace Model BAe 146 Series 
Airplanes and Model Avro 146-RJ 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 certain British Aerospace Model 
BAe 146 and Model Avro 146-RJ series airplanes. This proposal would 
require repetitive tests of the integrity of the electrical circuit 
between the windshear computer and the flap position sensor, and repair 
of the electrical wiring, if necessary. This proposal also would 
require replacement of certain windshear computers with new computers, 
which, when accomplished, terminates the repetitive tests. This 
proposal is prompted by a report indicating that the existing windshear 
computer is not capable of detecting a signal indicating loss of flap 
position; this could result in the flightcrew following erroneous 
computer-generated guidance. The actions specified by the proposed AD 
are intended to prevent the incapability of the windshear computer to 
detect the true flap position, which, if not corrected, could result in 
the inability of the flightcrew to avoid a windshear encounter, and 
consequent reduced controllability of the airplane.

DATES: Comments must be received by October 4, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-40-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.
    The service information referenced in the proposed rule may be 
obtained from British Aerospace Regional Aircraft Limited, Avro 
International Aerospace Division, Customer Support, Woodford Aerodrome, 
Woodford, Cheshire SK7 1QR, England. This information may be examined 
at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., 
Renton, Washington.

FOR FURTHER INFORMATION CONTACT: Tim Backman, Aerospace Engineer, 
Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 
227-2797; fax (206) 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

[[Page 43693]]

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 96-NM-40-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-103, Attention: Rules 
Docket No. 96-NM-40-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The Civil Aviation Authority (CAA), which is the airworthiness 
authority for the United Kingdom, recently notified the FAA that an 
unsafe condition may exist on certain British Aerospace Model BAe 146 
and Model Avro 146-RJ series airplanes. The CAA advises that it 
received a report indicating that the windshear computer installed on 
these airplanes is not capable of detecting a signal indicating loss of 
flap position. During a windshear encounter, the windshear computer 
displays guidance on the flight directors. This guidance indicates to 
the flightcrew to avoid windshear. The recommended flight maneuver in 
such cases depends upon many factors, including flap position. However, 
if the windshear computer is unable to detect the true flap position 
because the signal that indicates loss of flap position is not 
detected, the flightcrew could follow erroneous computer-generated 
guidance. This condition, if not corrected, could result in inability 
to avoid a windshear encounter and consequent reduced controllability 
of the airplane.

Explanation of Relevant Service Information

    Avro International Aerospace has issued Alert Inspection Service 
Bulletin S.B. 34-A155, Revision 2, dated August 9, 1995, which 
describes procedures for repetitive tests of the integrity of the 
electrical circuit between the windshear computer and the flap position 
sensor, and repair of the electrical wiring, if necessary. The CAA 
classified this service bulletin as mandatory in order to assure the 
continued airworthiness of these airplanes in the United Kingdom.
    Additionally, British Aerospace has issued Modification Service 
Bulletin SB.34-160-70548A, dated November 21, 1994, which describes 
procedures for replacement of existing windshear computers with new 
Safe Flight windshear computers. The new computer is capable of 
detecting an open circuit failure in the flap position input circuit. 
Accomplishment of the replacement also involves changing the polarity 
of the polarizing keys to preclude installation of lesser standard 
computers. Accomplishment of the replacement eliminates the need for 
the repetitive tests described previously. The CAA has approved the 
technical content of this service bulletin.

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. Pursuant 
to this bilateral airworthiness agreement, the CAA has kept the FAA 
informed of the situation described above. The FAA has examined the 
findings of the CAA, reviewed all available information, and 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, the 
proposed AD would require repetitive tests of the integrity of the 
electrical circuit between the windshear computer and the flap position 
sensor, and repair of the electrical wiring, if necessary. The proposed 
AD also would require replacement of existing windshear computers with 
new Safe Flight windshear computers. Accomplishment of the replacement 
would constitute terminating action for the repetitive tests. The 
actions would be required to be accomplished in accordance with the 
service bulletins described previously.

Differences Between FAA's Proposed Action and the CAA's Action

    Operators should note that, although the CAA did not classify the 
modification service bulletin as mandatory, this proposed AD would 
require accomplishment of the replacement described in that service 
bulletin within 6 months after the effective date of the AD. The FAA 
finds that accomplishment of continued repetitive tests could increase 
the likelihood of other failures. In addition, tests in accordance with 
the inspection service bulletin only verify the condition of the system 
at the time the tests are performed, and may not reliably predict 
future system performance. The FAA has determined that long term 
continued operational safety will be better assured by replacement of 
the windshear computers to remove the source of the problem, rather 
than by repetitive tests. Long term testing may not be providing the 
degree of safety assurance necessary for the transport airplane fleet. 
This, coupled with a better understanding of the human factors 
associated with numerous repetitive tests, has led the FAA to consider 
placing less emphasis on special procedures and more emphasis on design 
improvements. The proposed replacement requirement is in consonance 
with these considerations.

Explanation of Proposed Compliance Time for Replacement

    In developing an appropriate compliance time for the proposed 
replacement, the FAA's intent is that it be performed during a 
regularly scheduled maintenance visit for the majority of the affected 
fleet, when the airplanes would be located at a base where special 
equipment and trained personnel would be readily available, if 
necessary. The FAA finds that 6 months corresponds closely to the 
interval representative of most of the affected operators' normal 
maintenance schedules. The FAA considers that this interval will 
provide an acceptable level of safety.

Cost Impact

    The FAA estimates that 41 airplanes of U.S. registry would be 
affected by this proposed AD, that it would take approximately 1 work 
hour per airplane to accomplish the proposed test, and that the average 
labor rate is $60 per work hour. Based on these figures, the cost 
impact of the proposed test on U.S.

[[Page 43694]]

operators is estimated to be $2,460, or $60 per airplane, per test 
cycle.
    The FAA estimates that it would take approximately 4 work hours per 
airplane to accomplish the proposed replacement, at an average labor 
rate of $60 per work hour. Required parts would be supplied by the 
manufacturer at no cost to operators. Based on these figures, the cost 
impact of the proposed replacement on U.S. operators is estimated to be 
$9,840, or $240 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this AD were not adopted.

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:

British Aerospace: Docket 96-NM-40-AD.

    Applicability: Model BAe 146 and Model Avro 146-RJ series 
airplanes on which BAe Modification HCM40270A or HCM40270B (Safe 
Flight Windshear Computer) has been installed; 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 (e) 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 the inability of the flightcrew to avoid a windshear 
encounter and consequent reduced controllability of the airplane due 
to the inability of the windshear computer to detect the true flap 
position, accomplish the following:
    (a) Within 300 landings or 60 days after the effective date of 
this AD, whichever occurs first: Perform a test of the integrity of 
the electrical circuit between the windshear computer and the flap 
position sensor, in accordance with Avro International Aerospace 
Alert Inspection Service Bulletin S.B. 34-A155, Revision 2, dated 
August 9, 1995. Repeat the test thereafter at intervals not to 
exceed 300 landings until the actions required by paragraph (c) of 
this AD are accomplished.
    (b) If any test required by paragraph (a) of this AD fails, 
prior to further flight, repair the electrical wiring in accordance 
with Avro International Aerospace Alert Inspection Service Bulletin 
S.B. 34-A155, Revision 2, dated August 9, 1995. Thereafter, repeat 
the test required by paragraph (a) of this AD at intervals not to 
exceed 300 landings until the actions required by paragraph (c) of 
this AD are accomplished.
    (c) Within 6 months after the effective date of this AD: Replace 
any Safe Flight windshear computer having part number 6508-2 or 
6508-4 with a new Safe Flight windshear computer having part number 
6508-5; and change the polarity of the polarizing keys; in 
accordance with British Aerospace Modification Service Bulletin 
SB.34-160-70548A, dated November 21, 1994. Accomplishment of these 
actions constitutes terminating action for the repetitive tests 
required by paragraph (a) of this AD.
    (d) As of the effective date of this AD, no person shall install 
a Safe Flight windshear computer having part number 6508-2 or 6508-4 
on any airplane.
    (e) 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 Maintenance Inspector, 
who may add comments and then send it to the Manager, 
Standardization Branch, ANM-113.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Standardization Branch, ANM-113.

    (f) 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 August 19, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-21594 Filed 8-23-96; 8:45 am]
BILLING CODE 4910-13-U