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

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