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

Comments Invited

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

proposed rule. The proposals contained in this notice may be changed in light of the comments received. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of 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 That AD superseded, and retained certain requirements of AD 95-06-01, which was prompted by reports indicating that several center drive units (CDU) were returned to the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

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:

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.

(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