[Federal Register Volume 59, Number 205 (Tuesday, October 25, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-25294]


[[Page Unknown]]

[Federal Register: October 25, 1994]


-----------------------------------------------------------------------


DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 93-NM-122-AD; Amendment 39-9047; AD 94-21-05]

 

Airworthiness Directives; Boeing Model 737-300, -400, and -500 
Series Airplanes Equipped With CFM International CFM56-3 Series Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 737-300, -400, and -500 series 
airplanes, that requires modification, adjustments, and tests of the 
thrust reverser system; and repair, if necessary. This amendment is 
prompted by results of a safety review of the thrust reverser system on 
these airplanes, which revealed that the installation of additional 
features to further minimize the likelihood of an in-flight thrust 
reverser deployment is necessary. The actions specified by this AD are 
intended to prevent deployment of a thrust reverser in flight and 
subsequent reduced controllability of the airplane.

DATES: Effective November 25, 1994. -
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of November 25, 1994.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. 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: Stephen Bray, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (206) 227-2681; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes was published in the Federal Register on 
October 15, 1993 (58 FR 53457). That action proposed to require 
modification, adjustments, and tests of the thrust reverser system; and 
repair, if necessary. -
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received. -
    One commenter supports the proposed rule. -
    One commenter requests that paragraph (c) of the proposal be 
revised to specify that the paragraph applies to airplanes identified 
in the effectivity listing of Boeing Service Bulletin 737-78-1058. The 
commenter indicates that paragraph (c), as proposed, would require 
modification of airplanes on which the sync-lock was installed in 
production, but on which no additional rework was required. Further, as 
proposed, paragraph (c) would include airplanes that are not listed in 
the effectivity listing of Boeing Service Bulletin 737-78-1058. The FAA 
concurs, and has revised paragraph (c) of the final rule accordingly. 
However, airplanes on which the sync-lock was installed during 
production continue to be subject to the repetitive integrity test 
required by paragraph (d) of the final rule. Paragraph (d) of the final 
rule has been revised to clarify that requirement, and a new paragraph 
(e) has been included in the final rule to specify the compliance times 
for accomplishment of that requirement.
    The Air Transport Association (ATA) of America states that, while 
its members are not opposed to accomplishing periodic operational tests 
of the sync-lock following its installation [proposed in paragraph (d) 
of the AD] as part of their maintenance programs, these members are 
opposed to accomplishing the tests as part of the requirements of an 
AD. The ATA members believe that the requirement for operational tests 
is equivalent to issuing a Certification Maintenance Requirements (CMR) 
item by means of an AD. -
    ATA adds that, if the FAA finds sufficient justification to include 
the requirement for operational tests in the AD, an alternative to 
accomplishment of the tests should be provided in the final rule. ATA 
reasons that an alternative is justified because no data exist to show 
that repetitive tests of a modified thrust reverser cannot be handled 
adequately through an operator's maintenance program. The suggested 
alternative follows: Within 3 months after accomplishing the sync-lock 
installation, revise the FAA-approved maintenance inspection program to 
include an operational test of the sync-lock. The initial test would be 
accomplished within 1,000 hours time-in-service after modification. The 
AD would no longer be applicable for operators that have acceptably 
revised the maintenance program. Operators choosing this alternative 
could use an alternative recordkeeping method in lieu of that required 
by Secs. 91.417 or 121.380 of the Federal Aviation Regulations (FAR) 
(14 CFR 91.417 or 121.380). The FAA would be defined as the cognizant 
Principal Maintenance Inspector (PMI) for operators electing this 
alternative. -
    The FAA recognizes the concerns of the commenter regarding the 
requirement for periodic operational tests of the sync-lock following 
its installation. However, the FAA finds that these tests are necessary 
to provide an adequate level of safety and to ensure the integrity of 
the sync-lock installation. The actions required by this AD are 
consistent with actions that have been identified by an industry-wide 
task force as necessary to ensure adequate safety of certain thrust 
reverser systems installed on transport category airplanes. 
Representatives of the Aerospace Industries Association (AIA) of 
America, Inc., and the FAA comprise that task force. Representatives 
from other organizations, such as ATA, have participated in various 
discussions and work activities resulting from the recommendations of 
the task force. -
    The FAA acknowledges that the operational tests specified in this 
AD and CMR items are similar in terms of scheduled maintenance and 
recordkeeping. This AD addresses an unsafe condition and requires 
installation of the sync-lock to correct that unsafe condition. The FAA 
has determined that the requirement for operational tests is necessary 
to ensure the effectiveness of that installation in addressing the 
unsafe condition. This determination is based on the fact that the 
sync-lock is a new design whose reliability has not been adequately 
proven through service experience. In addition, service experience to 
date has demonstrated that failures can occur within the sync-lock that 
may not be evident during normal operation of the thrust reverser 
system and may not result in activation of the sync-lock ``unlock'' 
indicator. The ATA's suggested alternative to accomplishment of the 
operational tests would permit each operator to determine whether and 
how often these tests should be conducted. In light of the severity of 
the unsafe condition, however, the FAA has determined that allowing 
this degree of operator discretion is not appropriate at this time. 
Therefore, this AD is necessary to ensure that operators accomplish 
tests of the integrity of the sync-lock installation in a common manner 
and at common intervals. -
    Two commenters question why the proposed operational tests would be 
required at more frequent intervals following installation of an 
additional safety feature than prior to its installation. One of these 
commenters suggests that Boeing should prove the reliability of the 
system prior to its operation, and that the operational tests should be 
required at intervals not to exceed 3,000 hours time-in-service.
    -Several commenters also suggest that the installation of an 
additional safety feature, in addition to the fact that no failures of 
the system have occurred, should allow tests at ``C'' check intervals. 
Another commenter states that accomplishment of the tests at ``2B'' 
check intervals (or 1,100 hours time-in-service) would be more 
appropriate. One of these commenters states that a trial test period of 
the installation by several airlines would be in order.
    -The FAA has reconsidered the compliance time specified in 
paragraph (d) of the proposal [identified in paragraph (e) of the final 
rule] for accomplishment of an initial operational test, as well as the 
interval specified for accomplishment of repetitive operational tests. 
In light of the safety implications of the unsafe condition addressed 
and the practical aspects of accomplishing orderly operational tests of 
the fleet during regularly scheduled maintenance where special 
equipment and trained maintenance personnel will be readily available, 
the FAA finds that the compliance times specified in paragraph (e) of 
the AD may be extended without compromising safety. The FAA has 
determined that an interval of 4,000 hours time-in-service corresponds 
more closely to the interval at which most of the affected operators 
conduct regularly scheduled ``C'' checks. Therefore, paragraph (e) of 
the final rule has been revised to require accomplishment of the 
initial test within 4,000 hours time-in-service and accomplishment of 
repetitive tests at intervals not to exceed 4,000 hours time-in-
service.
    -One commenter requests that the FAA review the requirement for 
periodic operational tests specified in paragraph (d) of the proposal 
because these tests only address a sync-lock failing in the unlocked 
state. The commenter states that the sync-lock will be totally 
transparent to the flight crew. Therefore, if a sync-lock fails in the 
``locked'' state, the only indication the flight crew will receive is 
that when reverse thrust is applied, the reverser handles will be 
stopped by the interlock system and not allowed to move into reverse 
thrust.
    -The FAA considers that the operational tests required by paragraph 
(d) of this AD are adequate to address both the unlocked state and the 
locked state. The design of the sync-lock is fail-safe in the locked 
state; its failure in that state during flight would not result in 
deployment of a thrust reverser. In addition, failure of a sync-lock in 
the locked state during landing of the airplane does not present an 
unsafe condition. The airplane can be stopped within the distance 
specified in the Airplane Flight Manual (AFM) without the use of thrust 
reversers. The stopping distance specified in the AFM does not take 
credit for the additional stopping capabilities of the thrust reverser.
    -Three commenters request revisions to the compliance times 
specified in paragraph (a) of the proposal for accomplishment of 
initial and repetitive adjustments and tests of the thrust reverser 
system. One of these commenters requests that the proposed 30-day 
compliance time for the initial adjustments and tests be extended to 60 
days to accomplish these actions on all of the airplanes in its fleet. 
The commenter believes that a compliance time of 60 days is more 
appropriate in light of the fact that no major thrust reverser 
anomalies have been found.
    -Two of these commenters request that the proposed compliance time 
for accomplishment of the repetitive adjustments and tests specified in 
paragraph (a) of the proposal be revised to ``3,000 hours time-in-
service, or at each `C' check, whichever occurs later.'' One of the 
commenters believes that the compliance interval specified in the 
proposal is overly restrictive, and that the suggested revision would 
allow for accomplishment of testing and repairs at a time that 
coincides with regularly scheduled maintenance.
    -The FAA concurs with these commenters' requests to revise the 
compliance times for the initial and repetitive adjustments and tests 
required by paragraph (a) of the final rule. The FAA's intent was that 
these adjustments and tests be conducted 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. In light of 
this consideration, the FAA has determined that an extension of the 
compliance time for the initial adjustments and tests to 60 days, and 
an extension of the repetitive interval to 4,000 hours time-in-service, 
will not affect safety adversely. Paragraph (a) of the final rule has 
been revised accordingly.
    -Several commenters question the references to certain pages of the 
Boeing 737 Maintenance Manual cited in paragraphs (a) and (d) of the 
proposal. ATA requests that a statement be added to those paragraphs to 
allow operators to use later versions of the Maintenance Manual, 
provided that no substantive change is included in those later 
versions. One commenter points out that since certain Maintenance 
Manual pages referenced in the proposal have already been revised, 
operators must seek approval from the FAA for an alternative method of 
compliance in order to deviate from the Maintenance Manual pages cited 
in the AD. One commenter mentions that the Maintenance Manual page 
numbers cited in paragraph (d) of the proposal do not exist. Two 
commenters state that the specific Maintenance Manual pages referenced 
in the proposal include a number of tests that are redundant and 
unnecessary. One commenter states that the tests specified in paragraph 
(a) are normally performed after component replacement or after a 
system error has occurred. The commenter indicates that performing the 
``Normal Operation Test'' and the ``Auto-Restow Test,'' in addition to 
using the thrust reverser during normal flight operations, will satisfy 
all testing requirements for the thrust reverser.
    -Boeing requests specifically that the proposal be revised to 
include copies of the procedures for the required tests so that 
reference to the Maintenance Manual is not necessary. Boeing explains 
that the Maintenance Manuals are customized for each operator to 
reflect all of the equipment in that operator's fleet. Therefore, the 
number of pages for any given procedure is variable, depending on the 
number of different equipment configurations documented in an 
operator's Maintenance Manual. Boeing also indicates that Maintenance 
Manual procedures are revised periodically for non-technical reasons. 
Boeing adds that changes to the structure of the procedures are 
necessary to accommodate an upgrade of the publishing system that is 
currently under way, which, in addition to repagination, will 
necessitate the issuance of revised Maintenance Manual pages.
    -Boeing states that the effect of specifying Maintenance Manual 
page numbers and revision dates in the AD is that operators may be 
unable to use the procedure contained in the Maintenance Manual to 
perform certain tests required by the AD. Each operator would be 
required to maintain an obsolete version of the procedure, or to 
request FAA approval of an alternative method of compliance with the AD 
that would allow the use of the current version of the Maintenance 
Manual.
    -The FAA concurs partially. In light of the information submitted 
by the commenters, the FAA finds that specific reference to page 
numbers and dates of the Boeing 737 Maintenance Manual should not be 
specified in paragraph (a) of the final rule. However, for that 
paragraph, the FAA does not agree that copies of the specific 
procedures should be included in the final rule. Therefore, paragraph 
(a) of the final rule has been revised to cite only the appropriate 
section specified in the Maintenance Manual for accomplishment of the 
tests required by that paragraph. The procedures specified in that 
section of the Maintenance Manual contain the appropriate tests 
recommended by the manufacturer for verification of the proper 
operation of the thrust reverser system. However, the FAA would 
consider requests from individual operators for approval of use of 
alternative test procedures, in accordance with the provisions of 
paragraph (f) of this AD.
    -Subsequent to the issuance of the proposal and the receipt of 
Boeing's comments to the proposal, Boeing has submitted to the FAA 
separate procedures for accomplishment of the operational tests of the 
sync-lock integrity following its installation. The FAA has included 
these procedures in paragraph (d) of the final rule; therefore, the 
Maintenance Manual references specified in paragraph (d) of the 
proposal have been removed from the final rule.
    -One commenter requests that the compliance times be expressed in 
terms of cycles, instead of operating hours, since degradation of the 
thrust reverser system is related to cycles. The FAA does not concur. 
The FAA finds that the simplest expression of compliance times for 
purposes of this AD is in terms of a specific number of hours of 
operation at which compliance is required for affected airplanes. The 
FAA based this determination on the fact that the maintenance program 
for these airplanes is based on operating hours, the Maintenance Manual 
specifies compliance in terms of operating hours, and the maintenance 
program is based on operating hours. Further, recommended compliance 
intervals reflected in a safety assessment completed for the affected 
airplane/engine combination were expressed in terms of hours time-in-
service.
    -Two commenters request that the proposed 5-year compliance time 
for accomplishing the sync-lock installation be revised to 6 years to 
allow airplanes to be modified during scheduled heavy maintenance 
visits. The FAA does not concur with the commenters' requests to extend 
the compliance time. In developing an appropriate compliance time for 
this action, the FAA considered the safety implications, parts 
availability, and normal maintenance schedules for timely 
accomplishment of the modification. In consideration of these items, as 
well as input from the manufacturer with regard to parts availability, 
and industry representatives with regard to incorporation schedules, 
the FAA has determined that 5 years represents the maximum interval of 
time allowable wherein the modification can reasonably be accomplished 
and an acceptable level of safety can be maintained.
    ATA, on behalf of one of its members, requests that paragraphs (a) 
and (d) of the proposal be revised to provide an option for operators 
to lock out a thrust reverser that fails the tests required by those 
paragraphs in order to avoid unnecessary flight delays and 
cancellations. The commenter states that the Boeing 737 Master Minimum 
Equipment List (MMEL) presently grants this relief, provided that the 
thrust reverser in question is properly locked out.
    The FAA concurs partially. The FAA agrees that an option for 
dispatch relief should be allowed in accordance with the existing 
provisions and limitations specified in the MMEL. Paragraph (a) of the 
final rule has been revised accordingly. However, for airplanes on 
which a sync-lock is installed, the FAA, in conjunction with the Model 
757/767 Thrust Reverser Working Group, finds that a thrust reverser may 
be locked out, but the sync-lock must be operational at all times in 
order to ensure safe flight. Paragraph (d) of the final rule has been 
revised accordingly.
    The FAA also has revised paragraph (a) of the final rule to specify 
that only airplanes on which the sync-lock installation, the sync-lock 
wiring modification, or Production Revision Record (PRR) 35105 has not 
been accomplished are subject to the requirements of that paragraph.
    Two commenters suggest that the work hour estimates for 
accomplishment of the adjustments and tests [specified in paragraph (a) 
of the proposal] and operational tests [specified in paragraph (d) of 
the proposal] be increased. One commenter states that an estimate of 2 
work hours is more realistic for accomplishment of the adjustments and 
tests. The second commenter states that the operational tests would 
actually take approximately 2.5 work hours. The FAA does not concur. 
The information provided by the manufacturer to the FAA indicates that 
the adjustments/tests and the operational tests each take approximately 
one hour to accomplish. The FAA established its work hour estimate 
based on that information.
    ATA requests that the FAA coordinate with Boeing a revision to the 
service bulletin to incorporate a change for routing certain wiring, 
since one ATA member had to deviate from the service bulletin 
instructions to route certain wire bundles. The commenter does not 
specify the service bulletin it recommends be revised.
    The FAA has coordinated with Boeing all requests from operators 
concerning wire bundle routing, and has ensured that any necessary 
changes to service bulletin instructions have been incorporated in 
subsequent revisions to the service bulletins cited in this final rule. 
A summary of service bulletin revisions reviewed and approved by the 
FAA since the issuance of the proposed rule follows:
    1. Boeing Service Bulletin 737-78-1053, Revision 2, dated February 
17, 1994, and Revision 3, dated June 30, 1994: Revision 2 of the 
service bulletin adds notes explaining that certain wire bundles were 
installed in production on some of the affected airplanes, that 
installation of these wire bundles is not necessary for those 
airplanes, and that wire bundle W084 is necessary on only some of the 
affected airplanes. Certain revised drawings also are included in 
Revision 2, one subkit number is corrected, a list of fasteners is 
added, and procedures for installation of splices is added.
    Revision 3 of the service bulletin provides procedures for 
replacement of different aluminum foil markers on a particular circuit 
breaker panel on some airplanes.
    Paragraph (b) of the final rule has been revised to reflect 
Revisions 2 and 3 of this service bulletin as additional sources of 
service information.
    2. Boeing Service Bulletin 737-78-1058, Revision 1, dated February 
17, 1994, and Revision 2, dated July 7, 1994: Revision 1 of the service 
bulletin includes a list of fasteners and provides procedures for 
removal of two panels for access to the J20 box assembly and related 
wiring. That revision also provides improved procedures for removal of 
the thrust reverser manual drive units and installation of the sync-
locks.
    Revision 2 of the service bulletin revises certain test procedures 
for the thrust reverser system.
    Paragraph (c) of the final rule has been revised to reflect 
Revisions 1 and 2 of this service bulletin as additional sources of 
service information.
    The FAA has revised the applicability of the final rule to clarify 
its intent that the AD applies to Model 737-300, -400, and -500 series 
airplanes equipped with CFM International CFM56-3 series engines. The 
applicability of the proposed rule stated incorrectly that Model 737-
300, -400, and -500 series airplanes equipped with General Electric 
CFM56 series engines were affected by this AD.
    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 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.
    It should be noted that no evidence currently exists that in-flight 
deployment of a thrust reverser was responsible for the accident 
involving a Boeing Model 737-300 series airplane that occurred on 
September 8, 1994.
    There are approximately 1,079 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 531 
airplanes of U.S. registry will be required to accomplish adjustments 
and tests of the thrust reverser system, installation of the sync-lock, 
and operational tests of the sync-lock installation. The FAA estimates 
that it will take approximately 1 work hour per airplane to accomplish 
the required adjustments and tests, 198 work hours to accomplish the 
required installation, and 1 work hour to accomplish the required 
operational tests. The average labor rate is $55 per work hour. Based 
on these figures, the total cost impact of the AD on U.S. operators of 
airplanes on which the sync-lock feature was not installed during 
production or as a modification is estimated to be $5,841,000, or 
$11,000 per airplane.
    The FAA estimates that 8 airplanes of U.S. registry will be 
required to accomplish adjustments and tests of the thrust reverser, 
modification of the sync-lock wiring, and operational tests of the 
sync-lock installation. The FAA estimates that it will take 
approximately 1 work hour to accomplish the required adjustments and 
tests, 70 work hours to accomplish the required wiring modification, 
and 1 work hour to accomplish the required operational tests. The 
average labor rate is $55 per work hour. Based on these figures, the 
total cost impact of the AD on U.S. operators of airplanes on which the 
sync-lock feature was installed during production or as a modification 
is estimated to be $31,680, or $3,960 per airplane.
    Based on these figures, the total cost impact of the AD on U.S. 
operators is estimated to be $5,872,680.
    The total cost impact figure discussed above is 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.
    The FAA recognizes the large number of work hours required to 
accomplish the modification. The 5-year compliance time specified in 
paragraphs (b) and (c) of this AD should allow the sync-lock 
installation and wiring modification to be accomplished coincidentally 
with scheduled major airplane inspection and maintenance activities, 
thereby minimizing the costs associated with special airplane 
scheduling.
    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 14 CFR 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. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

94-21-05 Boeing: Amendment 39-9047. Docket 93-NM-122-AD.

    Applicability: Model 737-300, -400, and -500 series airplanes 
equipped with CFM International CFM56-3 series engines, certificated 
in any category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent deployment of a thrust reverser in flight and 
subsequent reduced controllability of the airplane, accomplish the 
following:
    (a) For airplanes on which the sync-lock installation [specified 
in paragraph (b) of this AD], sync-lock wiring modification 
[specified in paragraph (c) of this AD], or Production Revision 
Record (PRR) 35105 has not been accomplished: Within 60 days after 
the effective date of this AD, and thereafter at intervals not to 
exceed 4,000 hours time-in-service, perform adjustments and tests of 
the thrust reverser system that are specified in Section 78-31-00 of 
the Boeing 737 Maintenance Manual to verify proper operation of the 
thrust reverser system, in accordance with that section of the 
maintenance manual. If any discrepancy is found, prior to further 
flight, accomplish either paragraph (a)(1) or (a)(2) of this AD.
    (1) Repair any discrepancy found, in accordance with procedures 
described in the Boeing 737 Maintenance Manual. Or
    (2) Deactivate the associated thrust reverser in accordance with 
the existing provisions and limitations specified in the Master 
Minimum Equipment List (MMEL).
    (b) For airplanes on which the sync-lock feature was not 
installed during production or as a modification in accordance with 
Boeing Service Bulletin 737-78-1053, dated December 17, 1992: Within 
5 years after the effective date of this AD, install an additional 
thrust reverser system locking feature (sync-lock installation) in 
accordance with Boeing Service Bulletin 737-78-1053, Revision 1, 
dated July 1, 1993; Revision 2, dated February 17, 1994; or Revision 
3, dated June 30, 1994. Installation of the additional locking 
feature constitutes terminating action for the tests required by 
paragraph (a) of this AD.
    (c) For airplanes listed in Boeing Service Bulletin 737-78-1058, 
dated July 1, 1993: Within 5 years after the effective date of this 
AD, modify the sync-lock wiring in accordance with Boeing Service 
Bulletin 737-78-1058, dated July 1, 1993; Revision 1, dated February 
17, 1994; or Revision 2, dated July 7, 1994. Modification of the 
sync-lock wiring constitutes terminating action for the tests 
required by paragraph (a) of this AD.
    (d) At the times specified in paragraph (e) of this AD, 
accomplish the ``Thrust Reverser Sync-lock Integrity Test'' 
specified below to verify that the sync-locks are not failing in the 
unlocked state. If any discrepancy is found, prior to further 
flight, accomplish paragraph (d)(1) or (d)(2) of this AD.
    (1) Repair any discrepancy found, in accordance with procedures 
specified in the Boeing 737 Maintenance Manual. Or
    (2) Deactivate the associated thrust reverser in accordance with 
the existing provisions and limitations specified in the MMEL. The 
sync-locks installed on the deactivated thrust reverser must remain 
operational.

``Thrust Reverser Sync-lock Integrity Test

1. General

    A. Use this procedure to test the integrity of the thrust 
reverser sync-locks. The procedure must be performed on each engine.

2. Thrust Reverser Sync-Lock Test

    A. Prepare for the Thrust Reverser Sync-Lock test.
    (1) Do the steps that follow to supply power to the thrust 
reverser system:
    (a) Make sure the thrust levers are in the idle position.
    (b) Make sure the thrust reversers are retracted and locked.
    (c) Make sure these circuit breakers on the P6 circuit breaker 
panel are closed:
    (1) Engine 1 thrust reverser cont sys
    (2) Engine 2 thrust reverser cont sys
    (3) Engine 2 thrust reverser cont sys-alt
    (4) Engine 1 thrust reverser ind sys
    (5) Engine 2 thrust reverser ind sys
    (6) Engine 1 Sync-lock
    (7) Engine 2 Sync-lock
    (8) Engine 2 Sync-lock-ALTN
    (9) Landing gear air/gnd relay and lights
    (10) Radio ALTM-2
    (d) Make sure this circuit breaker on the P18 circuit breaker 
panel is closed:
    (1) Radio ALTM-1
    (e) Supply electrical power.
    (f) Remove pressure from the A (for the left engine) or B (for 
the right engine) hydraulic system.
    B. Do the thrust reverser sync-lock test.
    (1) Move and hold the manual unlock lever on the upper actuator 
on both thrust reverser sleeves to the unlock position.
    (2) Make sure the thrust reverser sleeves did not move aft.
    (3) Move the left (right) reverse thrust lever up and rearward 
to the reverse thrust position.
    (4) Make sure both thrust reverser sleeves move aft 
(approximately 0.15 to 0.25 inch).
    (5) Release the manual unlock lever on the upper actuators.

    Warning: Make sure all persons and equipment are clear of the 
area around the thrust reverser. When you apply hydraulic pressure, 
the thrust reverser will extend and can cause injuries to persons or 
damage to equipment.

    (6) Pressurize the A (B) hydraulic system.
    (7) Make sure the thrust reverser extends.
    (8) Move the left (right) reverse thrust lever to the forward 
and down position to retract the thrust reverser.
    C. Put the airplane back to its usual condition.
    (1) Remove hydraulic pressure.
    (2) Remove electrical power.
    D. Repeat the thrust reverser sync-lock test on the other 
engine.''
    (e) Accomplish the test required by paragraph (d) of this AD at 
the times specified in paragraph (e)(1) or (e)(2) of this AD, as 
applicable.
    (1) For airplanes that are subject to the requirements of 
paragraphs (b) and (c) of this AD: Within 4,000 hours time-in-
service after accomplishing the modification required by paragraph 
(b) or (c) of this AD, as applicable, or within 4,000 hours time-in-
service after the effective date of this AD, whichever occurs later; 
and thereafter at intervals not to exceed 4,000 hours time-in-
service.
    (2) For all other airplanes: Within 4,000 total hours time-in-
service, or within 4,000 hours time-in-service after the effective 
date of this AD, whichever occurs later; and thereafter at intervals 
not to exceed 4,000 hours time-in-service.
    (f) 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: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (g) 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.
    (h) The installation and wiring modification shall be done in 
accordance with Boeing Service Bulletin 737-78-1053, Revision 1, 
dated July 1, 1993; Boeing Service Bulletin 737-78-1053, Revision 2, 
dated February 17, 1994; Boeing Service Bulletin 737-78-1053, 
Revision 3, dated June 30, 1994; Boeing Service Bulletin 737-78-
1058, dated July 1, 1993; Boeing Service Bulletin 737-78-1058, 
Revision 1, dated February 17, 1994; or Boeing Service Bulletin 737-
78-1058, Revision 2, dated July 7, 1994. This incorporation by 
reference was approved by the Director of the Federal Register in 
accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, 
Seattle, Washington 98124-2207. 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.
    (i) This amendment becomes effective on November 25, 1994.

    Issued in Renton, Washington, on October 6, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-25294 Filed 10-24-94; 8:45 am]
BILLING CODE 4910-13-U