[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]
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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.
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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
