[Federal Register Volume 64, Number 248 (Tuesday, December 28, 1999)]
[Proposed Rules]
[Pages 72575-72579]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-33568]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-79-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-200 and -300 Series 
Airplanes Equipped With General Electric CF6-80C2 Series Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing 
airworthiness directive (AD), applicable to certain Boeing Model 747-
200 and -300 series airplanes, that currently requires various 
inspections and functional tests to detect discrepancies of the thrust 
reverser control and indication system, and correction of any 
discrepancy found. This action would require installation of a 
terminating modification, and would add repetitive functional tests of 
that installation, and repair, if necessary. This proposal is prompted 
by the results of a safety review of the thrust reverser systems on 
Model 747 series airplanes. The actions specified by the proposed AD 
are intended to ensure the integrity of the fail safe features of the 
thrust reverser system by preventing possible failure modes in the 
thrust reverser control system that can result in inadvertent 
deployment of a thrust reverser during flight.

DATES: Comments must be received by February 11, 2000.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-79-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Dorr Anderson, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2684; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the

[[Page 72576]]

proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-79-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 99-NM-79-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On July 12, 1999, the FAA issued AD 99-15-08, amendment 39-11227 
(64 FR 39003, July 21, 1999), applicable to certain Boeing Model 747-
200 and -300 series airplanes, to require various inspections and 
functional tests to detect discrepancies of the thrust reverser control 
and indication system, and correction of any discrepancy found. That AD 
superseded, and retained certain requirements of AD 95-06-01, which was 
prompted by reports indicating that several center drive units (CDU) 
were returned to the manufacturer of the CDU's because of low holding 
torque of the CDU cone brake. The requirements of that AD are intended 
to ensure the integrity of the fail safe features of the thrust 
reverser system by preventing possible failure modes in the thrust 
reverser control system that could result in inadvertent deployment of 
a thrust reverser during flight.

Actions Since Issuance of Previous Rule

    In the preamble to AD 99-15-08, the FAA specified that the actions 
required by that AD were considered ``interim action'' and that the 
manufacturer was developing a modification to positively address the 
unsafe condition. The FAA indicated that it may consider further 
rulemaking action once the modification was developed, approved, and 
available. The manufacturer now has developed such a modification, and 
the FAA has determined that further rulemaking action is indeed 
necessary; this proposed AD follows from that determination.
    The FAA has prioritized the issuance of AD's for corrective actions 
for the thrust reverser system on Boeing airplane models following a 
1991 accident. Based on service experience, analyses, and flight 
simulator studies, it was determined that an in-flight deployment of a 
thrust reverser has more effect on controllability of twin-engine 
airplane models than of Model 747 series airplanes, which have four 
engines. For this reason, the highest priority was given to rulemaking 
that required corrective actions for the twin-engine airplane models. 
AD's correcting the same type of unsafe condition addressed by this AD 
have been previously issued for specific airplanes within the Boeing 
Model 737, 757 and 767 series.
    Service experience has shown that in-flight thrust reverser 
deployments have occurred on Model 747 airplanes during certain flight 
conditions with no significant airplane controllability problems being 
reported. However, the manufacturer has been unable to establish that 
acceptable airplane controllability would be achieved following these 
deployments throughout the operating envelope of the airplane. 
Additionally, safety analyses performed by the manufacturer and 
reviewed by the FAA, has been unable to establish that the risks for 
uncommanded thrust reverser deployment during critical flight 
conditions is acceptably low.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 747-78-
2144, Revision 1, dated April 1, 1996, which describes procedures for 
accomplishment of certain thrust reverser wiring modifications of the 
wings, strut, and fuselage. Boeing Service Bulletin 747-78-2144 
references the following service bulletins:
     Lockheed Martin Service Bulletin 78-1007, Revision 1, 
dated March 18, 1997, and Middle River Aircraft Systems Service 
Bulletin 78-1007, Revision 2, dated March 10, 1998, which describe 
procedures for adding an actuation system lock bracket and fastening 
hardware to each thrust reverser; and
     Lockheed Martin Service Bulletin 78-1020, Revision 2, 
dated March 20, 1997, and Middle River Aircraft Systems Service 
Bulletin 78-1020, Revision 3, dated March 16, 1998, which describe 
procedures for installation of an actuation system lock (also called an 
electro-mechanical lock or electro-mechanical brake) on each thrust 
reverser.
    Accomplishment of Boeing Service Bulletin 747-78-2144 requires 
prior or concurrent accomplishment of Lockheed Martin Service Bulletin 
78-1007, Revision 1, or Middle River Aircraft Systems Service Bulletin 
78-1007, Revision 2; and Lockheed Martin Service Bulletin 78-1020, 
Revision 2, or Middle River Aircraft Systems Service Bulletin 78-1020, 
Revision 3.
    The modification procedures described by Boeing Service Bulletins 
747-78-2144 were previously validated by the manufacturer, and the 
necessary changes have been incorporated into the latest revisions of 
the service bulletins. The FAA has determined that the procedures 
specified in Boeing Service Bulletin 747-78-2144, Revision 1, as well 
as the other service bulletins referenced in this proposed AD, have 
been effectively validated and therefore proposes that this 
modification be required. Several airplanes have been successfully 
modified in accordance with the service bulletins, and this past 
experience should minimize the likelihood for subsequent service 
bulletin revisions, requests for alternative methods of compliance, and 
superseding AD's.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would supersede AD 99-15-08 to continue to require various 
inspections and functional tests to detect discrepancies of the thrust 
reverser control and indication system, and correction of any 
discrepancy found. This proposed AD would require installation of a 
terminating modification, and would add repetitive functional tests of 
that installation, and repair, if necessary. The actions would be 
required to be accomplished in accordance with the service bulletins 
described previously, except as discussed below.

Differences Between Service Bulletins and This Proposed AD

    Operators should note that, although the service bulletins 
described previously recommend no specific compliance time for 
accomplishment of the actuation system lock installation, the FAA has 
determined that an unspecified compliance time would not address the 
identified unsafe condition

[[Page 72577]]

in a timely manner. In developing an appropriate compliance time for 
this AD, the FAA considered not only the manufacturer's recommendation, 
but the degree of urgency associated with addressing the subject unsafe 
condition, the average utilization of the affected fleet, and the time 
necessary to perform the installation. In light of all of these 
factors, the FAA finds a 36-month compliance time for completing the 
required actions to be warranted, in that it represents an appropriate 
interval of time allowable for affected airplanes to continue to 
operate without compromising safety.
    Operators also should note that this AD proposes to mandate, within 
36 months, accomplishment of the actions specified for installation of 
the actuation system lock as described in Lockheed Martin Service 
Bulletin 78-1007, Revision 1; Middle River Aircraft Systems Service 
Bulletin 78-1007, Revision 2; Lockheed Martin Service Bulletin 78-1020, 
Revision 2; Middle River Aircraft Systems Bulletin 78-1020, Revision 3; 
and Boeing Service Bulletin 747-78-2144, Revision 1; as terminating 
action for the requirements of AD 99-15-08, and paragraph (b) of AD 95-
06-01. Following accomplishment of the installation, the FAA has 
determined that repetitive functional tests of the CDU cone brake and 
actuation system lock on each thrust reverser will support continued 
operational safety of thrust reversers with actuation system locks.

Cost Impact

    There are approximately 9 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 2 airplanes of U.S. registry 
would be affected by this proposed AD.
    The actions originally required by AD 95-06-01, and retained in 
this proposed AD, take approximately 33 work hours per airplane to 
accomplish, at an average labor rate of $60 per work hour. Based on 
these figures, the cost impact of the currently required actions on 
U.S. operators is estimated to be $3,960, or $1,980 per airplane, per 
inspection/test cycle.
    The other actions (repeating the functional test of the cone brake 
required by AD 95-06-01 at reduced intervals) that are currently 
required by AD 99-15-08, and retained in this proposed AD, would not 
add any additional economic burden on affected operators.
    The bracket installation proposed in this new AD would take 
approximately 64 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Required parts would be provided by 
the manufacturer at no cost to the operators. Based on these figures, 
the cost impact of the bracket installation proposed by this AD on U.S. 
operators is estimated to be $7,680, or $3,840 per airplane.
    The actuation system lock installation proposed in this new AD 
would take approximately 16 work hours per airplane to accomplish, at 
an average labor rate of $60 per work hour. Required parts would be 
provided by the manufacturer at no cost to the operators. Based on 
these figures, the cost impact of the lock installation proposed by 
this AD on U.S. operators is estimated to be $1,920, or $960 per 
airplane.
    The functional test proposed in this new AD would take 
approximately 2 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of the functional test proposed by this AD on U.S. operators is 
estimated to be $240, or $120 per airplane, per test cycle.
    The wiring modifications proposed in this new AD would take 
approximately 833 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Required parts would be provided by 
the manufacturer at no cost to the operators. Based on these figures, 
the cost impact of the modifications proposed by this AD on U.S. 
operators is estimated to be $99,960, or $49,980 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-11227 (64 FR 
39003, July 21, 1999), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 99-NM-79-AD. Supersedes AD 99-15-08, amendment 39-
11227.

    Applicability: Model 747-200 and -300 series airplanes equipped 
with General Electric Model CF6-80C2 series engines with Power 
Management Control engine controls, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (h)(1) 
of this AD. The request should include an assessment of the effect 
of the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To ensure the integrity of the fail safe features of the thrust 
reverser system by preventing possible failure modes in the thrust 
reverser control system that can result in inadvertent deployment of 
a thrust reverser during flight, accomplish the following:

[[Page 72578]]

Restatement of the Original Requirements of AD 95-06-01

Repetitive Tests and Inspections

    (a) Within 90 days after April 13, 1995 (the effective date of 
AD 95-06-01, amendment 39-9171), perform tests of the position 
switch module and the cone brake of the center drive unit (CDU) on 
each thrust reverser, and perform an inspection to detect damage to 
the bullnose seal on the translating sleeve on each thrust reverser, 
in accordance with paragraphs III.A. through III.C. of the 
Accomplishment Instructions of Boeing Alert Service Bulletin 747-
78A2130, dated May 26, 1994. Repeat the tests and inspection 
thereafter at intervals not to exceed 1,000 hours time-in-service 
until the functional test required by paragraph (d) of this AD is 
accomplished.
    (b) Within 9 months after April 13, 1995, perform inspections 
and functional tests of the thrust reverser control and indication 
system in accordance with paragraphs III.D. through III.F., III.H., 
and III.I. of the Accomplishment Instructions of Boeing Alert 
Service Bulletin 747-78A2130, dated May 26, 1994. Repeat these 
inspections and functional tests thereafter at intervals not to 
exceed 18 months.

Corrective Action

    (c) If any of the inspections and/or functional tests required 
by paragraphs (a) and (b) of this AD cannot be successfully 
performed, or if any discrepancy is found during those inspections 
and/or functional tests, accomplish either paragraph (c)(1) or 
(c)(2) of this AD.
    (1) Prior to further flight, correct the discrepancy found, in 
accordance with Boeing Alert Service Bulletin 747-78A2130, dated May 
26, 1994. Or
    (2) The airplane may be operated in accordance with the 
provisions and limitations specified in an operator's FAA-approved 
Minimum Equipment List (MEL), provided that no more than one thrust 
reverser on the airplane is inoperative.

Restatement of Requirements of AD 99-15-08

Repetitive Tests/Terminating Action

    (d) Within 1,000 hours time-in-service after the most recent 
test of the CDU cone brake performed in accordance with paragraph 
(a) of this AD, or within 650 hours time-in-service after August 25, 
1999 (the effective date of AD 99-15-08, amendment 39-11227), 
whichever occurs first: Perform a functional test to detect 
discrepancies of the CDU cone brake on each thrust reverser, in 
accordance with Boeing Service Bulletin 747-78A2166, Revision 1, 
dated October 9, 1997, or paragraph III.B. of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 747-78A2130, dated May 
26, 1994. Repeat the functional test thereafter at the interval 
specified in paragraph (d)(1) or (d)(2) of this AD, as applicable. 
Accomplishment of such functional test constitutes terminating 
action for the repetitive test of the CDU cone brake required by 
paragraph (a) of this AD; the position switch module tests and the 
bullnose seal inspections continue to be required as specified in 
paragraph (a) of this AD.
    (1) For airplanes equipped with thrust reversers NOT modified in 
accordance with Boeing Service Bulletin 747-78-2144, Revision 1, 
dated April 11, 1996: Repeat the functional test at intervals not to 
exceed 650 hours time-in-service.
    (2) For airplanes equipped with thrust reversers modified in 
accordance with Boeing Service Bulletin 747-78-2144, Revision 1, 
dated April 11, 1996: Repeat the functional test at intervals not to 
exceed 1,000 hours time-in-service.

Corrective Action

    (e) If any functional test required by paragraph (d) of this AD 
cannot be successfully performed, or if any discrepancy is found 
during any functional test required by paragraph (d) of this AD, 
accomplish either paragraph (e)(1) or (e)(2) of this AD.
    (1) Prior to further flight, correct the discrepancy found, in 
accordance with Boeing Service Bulletin 747-78A2166, Revision 1, 
dated October 9, 1997, or paragraph III.B. of the Accomplishment 
Instructions of Boeing Alert Service Bulletin 747-78A2130, dated May 
26, 1994. Or
    (2) The airplane may be operated in accordance with the 
provisions and limitations specified in the operator's FAA-approved 
MEL, provided that no more than one thrust reverser on the airplane 
is inoperative.

New Requirements of This AD

Terminating Action

    (f) Accomplish the requirements of paragraphs (f)(1) and (f)(2) 
of this AD at the times specified in those paragraphs. 
Accomplishment of the actions required by paragraph (f)(1) of this 
AD constitutes terminating action for the requirements of paragraphs 
(a), (b), (d), and (e) of this AD.
    (1) Within 36 months after the effective date of this AD, 
accomplish the requirements of paragraphs (f)(1)(i) and (f)(1)(ii) 
of this AD.
    (i) Install an actuation system lock bracket and fastening 
hardware to each thrust reverser in accordance with the 
Accomplishment Instructions of Lockheed Martin Service Bulletin 78-
1007, Revision 1, dated March 18, 1997, or Middle River Aircraft 
Systems Service Bulletin 78-1007, Revision 2, dated March 10, 1998.
    (ii) Install an actuation system lock (also called an electro-
mechanical lock or electro-mechanical brake) on each thrust reverser 
in accordance with the Accomplishment Instructions of Lockheed 
Martin Service Bulletin 78-1020, Revision 2, dated March 20, 1997, 
or Middle River Aircraft Systems Service Bulletin 78-1020, Revision 
3, dated March 16, 1998.
    (2) Prior to or concurrent with the accomplishment of the 
requirements of paragraph (f)(1) of this AD, perform the thrust 
reverser wiring modifications of the wings, strut, and fuselage, in 
accordance with the Accomplishment Instructions of Boeing Service 
Bulletin 747-78-2144, Revision 1, dated April 11, 1996.

Repetitive Tests

    (g) Within 1,000 hours time-in-service after accomplishment of 
paragraph (f) of this AD, or within 1,000 hours time-in-service 
after the effective date of this AD, whichever occurs later: Perform 
a functional test to detect discrepancies of the CDU cone brake and 
actuation system lock on each thrust reverser, in accordance with 
Appendix 1 of this AD. Prior to further flight, correct any 
discrepancy detected and repeat the functional test of that repair, 
in accordance with the procedures described in the Boeing 747 
Maintenance Manual. Repeat the functional tests thereafter at 
intervals not to exceed 1,000 hours time-in-service.

Alternative Methods of Compliance

    (h)(1) 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.
    (2) Alternative methods of compliance, approved previously in 
accordance with AD 99-15-08, amendment 39-11227, are approved as 
alternative methods of compliance with the corresponding 
requirements specified in this AD.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (i) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

Appendix 1--Thrust Reverser Electro-Mechanical Brake and CDU Cone Brake 
Test

    1. General
    A. This procedure contains steps to do two checks:
    (1) A check of the holding torque of the electro-mechanical 
brake.
    (2) A check of the holding torque of the CDU cone brake.
    2. Electro-Mechanical Brake and CDU Cone Brake Torque Check
    A. Prepare to do the checks:
    (1) Open the fan cowl panels.
    B. Do a check of the torque of the electro-mechanical brake:
    (1) Do a check of the running torque of the thrust reverser 
system:
    (a) Manually extend the thrust reverser six inches and measure 
the running torque.
    (1) Make sure the torque is less than 10 pound-inches.
    (2) Do a check of the electro-mechanical brake holding torque:
    (a) Make sure the thrust reverser translating cowl is extended 
at least one inch.
    (b) Make sure the CDU lock handle is released.
    (c) Pull down on the manual release handle on the electro-
mechanical brake until the handle fully engages the retaining clip.

    Note: This will lock the electro-mechanical brake.


[[Page 72579]]


    (d) With the manual drive lockout cover removed from the CDU, 
install a \1/4\-inch extension tool and dial-type torque wrench into 
the drive pad.

    Note: You will need a 24-inch extension to provide adequate 
clearance for the torque wrench.

    (e) Apply 90 pound-inches of torque to the system.
    (1) The electro-mechanical brake system is working correctly if 
the torque is reached before you turn the wrench 450 degrees (1\1/4\ 
turns).
    (2) If the flexshaft turns more than 450 degrees before you 
reach the specified torque, you must replace the long flexshaft 
between the CDU and the upper angle gearbox.
    (3) If you do not get 90 pound-inches of torque, you must 
replace the electro-mechanical brake.
    (f) Release the torque by turning the wrench in the opposite 
direction until you read zero pound-inches.
    (1) If the wrench does not return to within 30 degrees of 
initial starting point, you must replace the long flexshaft between 
the CDU and upper angle gearbox.
    (3) Fully retract the thrust reverser.
    C. Do a check of the torque of the CDU cone brake:
    (1) Pull up on the manual release handle to unlock the electro-
mechanical brake.
    (2) Pull the manual brake release lever on the CDU to release 
the cone brake.

    Note: This will release the pre-load tension that may occur 
during a stow cycle.

    (3) Return the manual brake release lever to the locked position 
to engage the cone brake.
    (4) Remove the two bolts that hold the lockout plate to the CDU 
and remove the lockout plate.
    (5) Install a \1/4\-inch drive and a dial type torque wrench 
into the CDU drive pad.

    CAUTION: DO NOT USE MORE THAN 100 POUND-INCHES OF TORQUE WHEN 
YOU DO THIS CHECK. EXCESSIVE TORQUE WILL DAMAGE THE CDU.

    (6) Turn the torque wrench to try to manually extend the 
translating cowl until you get at lease 15-pound inches.

    Note: The cone brake prevents movement in the extend direction 
only. If you try to measure the holding torque in the retract 
direction, you will get a false reading.

    (a) If the torque is less than 15-pound-inches, you must replace 
the CDU.
    D. Return the airplane to its usual condition:
    (1) Re-install the lockout plate.
    (2) Fully retract the thrust reverser (unless already 
accomplished).
    (3) Pull down on the manual release handle on the electro-
mechanical brake until the handle fully engages the retaining clip 
(unless already accomplished).

    Note: This will lock the electro-mechanical brake.

    (4) Close the fan cowl panels.

    Issued in Renton, Washington, on December 21, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-33568 Filed 12-27-99; 8:45 am]
BILLING CODE 4910-13-U