[Federal Register Volume 64, Number 162 (Monday, August 23, 1999)]
[Proposed Rules]
[Pages 45927-45929]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-21846]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-101-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 757 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 Boeing Model 757 series 
airplanes. This proposal would require a modification of the reverse 
thrust lever assemblies and replacement of the spring bumper assemblies 
of the thrust reverser sleeves with new assemblies. This proposal is 
prompted by an FAA review of the thrust reverser system on all 
transport category airplanes including the Boeing Model 757 series 
airplane. The actions specified by the proposed AD are intended to 
prevent operation with an energized sync lock or malfunctioning sleeve 
locking devices, which could result in the deployment of a thrust 
reverser in flight and subsequent reduced controllability of the 
airplane.

DATES: Comments must be received by October 7, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-101-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 Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Kathrine Rask, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-1547; fax (425) 227-1181.

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

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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-101-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-101-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    Following a 1991 accident caused by deployment of a thrust reverser 
in flight on a Boeing Model 767 series airplane, the FAA initiated a 
special certification review of all transport category thrust reverser 
systems and airplane controllability in the event of deployment of a 
thrust reverser in flight. As a result of that review, Boeing 
developed, for certain Boeing airplane models, an additional thrust 
reverser locking system and conducted a safety assessment to determine 
the probability of deployment of a thrust reverser in flight. The 
safety assessment evaluates every possible combination of failures for 
the thrust reverser system that could result in deployment of a thrust 
reverser in flight, and considers the probability and detectability of 
each failure. The safety assessment for the Model 757 series airplane 
identified two failure conditions that, because they are latent 
failures, would significantly affect the reliability of the thrust 
reverser locking system and, in combination with other failures in the 
thrust reverser system, could result in deployment of a thrust reverser 
in flight and subsequent reduced controllability of the airplane. The 
two failure conditions are described below.
     Failure of the reverse thrust switch actuator causes the 
switch to remain in a powered position. The failure causes the thrust 
reverser sync lock to remain energized while the airplane is operated 
on the ground, during the takeoff roll, and possibly during the first 
two minutes of flight. This failure would not prevent normal operation 
of the thrust reverser; however, it would not be detected until the 
next sync lock integrity test was conducted.
     The spring bumper assembly pushes on the thrust reverser 
translating sleeve causing adequate sleeve movement, if the sleeve is 
unlocked, to activate the auto-restow system in flight or provide a 
visual indication of an unlocked sleeve during the ground walk-around 
inspection. If the spring bumper assembly fails, it is likely that a 
malfunctioning sleeve locking device would not be detected for several 
flight cycles.
    Should either of these failure conditions occur but remain 
undetected for an extended period, in the event of other failures in 
the thrust reverser system, the thrust reverser locking systems may not 
prevent deployment of a thrust reverser in flight.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 757-76-
0009, Revision 1, dated December 3, 1998, which describes procedures 
for a modification of the reverse thrust lever assemblies. This 
modification improves the reliability of the reverse thrust switch and 
changes the failed state of the switch, such that failure of the 
reverse thrust switch actuator does not result in latching of the relay 
and consequent energizing of the sync lock or opening of the isolation 
valve.
    The FAA has also reviewed and approved Boeing Service Bulletin 757-
78-0012, dated August 31, 1989, which describes procedures for 
replacement of the spring bumper assembly of the thrust reverser sleeve 
with a new spring bumper assembly with an improved service life. Such 
replacement ensures that a malfunctioning sleeve locking device will be 
detected within one flight cycle.
    Accomplishment of the actions specified in the service bulletins is 
intended to adequately address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require accomplishment of the actions specified in 
the service bulletins described previously.

Explanation of Applicability

    Certain airplanes listed in Boeing Service Bulletin 757-76-0009, 
Revision 1, may not need to be modified in accordance with that service 
bulletin. Certain Model 757 series airplanes powered by Pratt and 
Whitney Model PW2000 engines that are affected by Boeing Service 
Bulletin 757-76-0009, Revision 1, were delivered with reverse thrust 
switches that open the thrust reverser hydraulic isolation valves. On 
these airplanes, failure of the reverse thrust switch actuator causes 
the hydraulic isolation valve to remain open while the airplane is on 
the ground and during the takeoff roll. Such a failure would be 
detected through various engine indicating and crew alerting system 
(EICAS) messages within one flight. Therefore, because the failure 
would not go undetected for an extended period, the reliability of the 
thrust reverser locking system is not significantly affected, no unsafe 
condition exists, and these airplanes are not subject to the 
modification described in Boeing Service Bulletin 757-76-0009, Revision 
1.
    Certain other Model 757 series airplanes powered by Pratt and 
Whitney Model PW2000 engines that are affected by Boeing Service 
Bulletin 757-76-0009, Revision 1, have a redesigned switch function 
arrangement on which the reverse thrust switches energize the sync 
locks. (This redesign transfers control of the hydraulic isolation 
valve from the reverse thrust switches to the autothrottle switchpack 
switches.) On these airplanes, failure of the reverse thrust switch 
actuator causes the reverse thrust switch to remain in a powered 
position, which results in the thrust reverser sync lock remaining 
energized while the airplane is on the ground. Because there is no 
indication of such a failure, except from the sync lock integrity test, 
these airplanes would therefore be subject to the unsafe condition 
described previously.
    The FAA knows of operators of Boeing Model 757 series airplanes 
powered by Pratt and Whitney Model PW2000 engines that have 
incorporated the redesigned switch function arrangement. However, the 
FAA cannot define the extent of incorporation of this modification in 
the affected fleet; therefore, this proposed AD is applicable to all 
airplanes listed in Boeing Service Bulletin 757-76-0009, Revision 1 (in 
addition to those listed in Boeing Service Bulletin 757-78-0012). If an 
operator of Boeing Model 757 series airplanes powered by Pratt and 
Whitney Model PW2000 engines can determine that the reverse thrust 
switches, as defined in Boeing Service Bulletin 757-76-0009, Revision 
1, open the thrust reverser hydraulic isolation valves, that operator 
may request an alternative method of compliance in

[[Page 45929]]

accordance with paragraph (c) of this proposed AD.

Cost Impact

    There are approximately 308 airplanes of the affected design in the 
worldwide fleet.
    The FAA estimates that the proposed modification of the reverse 
thrust lever assemblies would be required to be accomplished on 169 
U.S. registered airplanes. It would take approximately 8 work hours per 
airplane to accomplish the proposed modification at an average labor 
rate of $60 per work hour. Required parts would cost approximately $29 
per airplane. Based on these figures, the cost impact of this proposed 
modification on U.S. operators is estimated to be $86,021, or $509 per 
airplane.
    The FAA estimates that the proposed replacement of the spring 
bumper assemblies would be required to be accomplished on 92 U.S. 
registered airplanes. It would take approximately 10 work hours per 
airplane to accomplish the proposed replacement at an average labor 
rate of $60 per work hour. Required parts would cost approximately 
$5,178 per airplane. Based on these figures, the cost impact of this 
proposed replacement on U.S. operators is estimated to be $531,576, or 
$5,778 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:

Boeing: Docket 99-NM-101-AD.

    Applicability: Model 757 series airplanes, as listed in Boeing 
Service Bulletin 757-76-0009, Revision 1, dated December 3, 1998, or 
Boeing Service Bulletin 757-78-0012, dated August 31, 1989; 
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 (c) 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 operation with an energized sync lock or 
malfunctioning sleeve locking devices, which could result in 
deployment of a thrust reverser in flight and subsequent reduced 
controllability of the airplane, accomplish the following:
    (a) For airplanes listed in Boeing Service Bulletin 757-76-0009, 
Revision 1, dated December 3, 1998: Within 2 years after the 
effective date of the AD, replace the reverse thrust switches and 
actuators with improved switches and actuators, and modify the 
reverse lever links and thrust control levers in accordance with the 
service bulletin.

    Note 2: Modifications accomplished prior to the effective date 
of this AD in accordance with Boeing Service Bulletin 757-76-0009, 
dated November 8, 1990, are considered acceptable for compliance 
with the applicable action specified in this amendment.

    (b) For airplanes listed in Boeing Service Bulletin 757-78-0012, 
dated August 31, 1989: Within 2 years after the effective date of 
the AD, replace the spring bumper assemblies of the thrust reverser 
sleeve with improved assemblies in accordance with the service 
bulletin.

Alternative Methods of Compliance

    (c) 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, Seattle Aircraft Certification 
Office (ACO), 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, Seattle ACO.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (d) 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 17, 1999.
D. L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-21846 Filed 8-20-99; 8:45 am]
BILLING CODE 4910-13-P