Airworthiness Directives; Boeing Model 747 Series Airplanes Equipped With Pratt & Whitney JT9D-70 Series Engines

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Boeing Model 747 series airplanes. This proposal would require inspections, tests, and certain modifications of the thrust reverser control and indication system and wiring on each engine, and corrective action, if necessary.

This proposal also would require installation of a terminating modification, and repetitive functional tests of that installation to detect discrepancies, and repair, if necessary. This proposal is prompted by the results of a safety review, which revealed that in-flight deployment of a thrust reverser could result in significant reduction in airplane controllability. 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, which could result in inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane.

DATES:

Comments must be received by March 20, 2000.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-65-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:

Larry Reising, Aerospace Engineer, Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2683; 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 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-65-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-65-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On May 26, 1991, a Boeing Model 767-300ER series airplane was involved in an accident as a result of an uncommanded in-flight deployment of a thrust reverser. Following that accident, a study was conducted to evaluate the potential effects of an uncommanded thrust reverser deployment throughout the flight regime of the Boeing Model 747 series airplane. The study included a re-evaluation of the thrust reverser control system fault analysis and airplane controllability. The results of the evaluation indicated that, in the event of thrust reverser deployment during high-speed climb using high engine power, these airplanes also could experience control problems. This condition, if not corrected, could result in possible failure modes in the thrust reverser control system, inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane.

The FAA has prioritized the issuance of AD's for corrective actions for the thrust reverser system on Boeing airplane models following the 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 the following Boeing Service Bulletins:

• 747-78A2159, dated May 18, 1995, which describes procedures for repetitive inspections and tests of the thrust reverser control and indication system to detect discrepancies, and corrective action, if necessary. The corrective action includes, among other things, repair or replacement of any discrepant parts with new parts.
• 747-78-2153, Revision 1, dated November 27, 1996, which describes procedures for installation of an additional locking system on the thrust reversers. This service bulletin references the following service bulletins:

1. Boeing Service Bulletin 747-78-2135, dated August 31, 1995, which describes procedures for the installation of provisional wiring for an additional thrust reverser locking device.

2. Boeing Service Bulletin 747-78A2149, Revision 1, dated May 9, 1996, and Revision 2, dated August 29, 1996, which describe procedures for inspection of the thrust reverser control system wiring to detect damaged wires; modification of certain wiring, and an operational test of the thrust reverser. This service bulletin references Boeing Standard Wiring Practices Manual, which describes procedures for repair or replacement of certain wire bundles, if necessary.

3. Rohr Service Bulletin TBC-CNS 78-33, Revision 1, dated August 20, 1996, which describes additional procedures for installation of an additional locking system on the thrust reversers.

Accomplishment of Boeing Service Bulletin 747-78-2153, Revision 1, requires prior or concurrent accomplishment of Boeing Service Bulletins 747-78-2135 and 747-78A2149, Revision 1 or Revision 2; and concurrent accomplishment of Rohr Service Bulletin TBC-CNS 78-33, Revision 1. Accomplishment of these actions would eliminate the need for certain repetitive inspections and tests.

The FAA also has reviewed and approved Rohr Service Bulletin TBC-CNS 78-32, Revision 1, dated August 20, 1996, which describes procedures for modification of the thrust reverser control system wiring concurrent with accomplishment of Boeing Service Bulletin 747-78A2149, Revision 1 or Revision 2.

The modification procedures described by Boeing Service Bulletins 747-78-2153, and 747-78-2135 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 Bulletins 747-78-2153, Revision 1, and 747-78-2135, as well as the other service bulletins referenced in this proposed AD, have been effectively validated and therefore proposes that this modification be required.

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, this proposed AD would require inspection of the thrust reverser control and indication system and wiring on each engine, and corrective action, if necessary; and eventual modification of the wiring. This proposal also would require installation of a terminating modification and repetitive functional tests of that installation to detect discrepancies, and repair, if necessary. The actions would be required to be accomplished in accordance with the service bulletins described previously, except as discussed below.

Repetitive functional tests to detect discrepancies of the actuation system lock on each thrust reverser would be required to be accomplished in accordance with the procedure included in Appendix 1 of this AD. Correction of any discrepancy detected would be required to be accomplished in accordance with the procedures described in the Boeing 747 Airplane Maintenance Manual.

Differences Between Service Bulletin and This Proposed AD

Operators should note that, although Boeing Service Bulletin 747-78-2153, Revision 1, does not recommend a 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, although the service bulletin does not specify repetitive functional testing of the actuation system lock installation following accomplishment of that installation, the FAA has determined that repetitive functional tests of the actuation system lock on each thrust reverser will support continued operational safety of thrust reversers with actuation system locks.

Cost Impact

There are approximately 7 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 6 airplanes of U.S. registry would be affected by this proposed AD.

It would take approximately 32 work hours (8 work hours per engine) per airplane, to accomplish the proposed thrust reverser inspection, modification, and test, described in 747-78A2149, Revision 1, or Revision 2, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be $11,520, or $1,920 per airplane.

It would take approximately 8 work hours (2 work hours per engine) per airplane, to accomplish the proposed 1,000-flight-hour inspections described in Boeing Service Bulletin 747-78A2159, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection proposed by this AD on U.S. operators is estimated to be $2,880, or $480 per airplane, per inspection cycle.

It would take approximately 20 work hours (5 work hours per engine) per airplane, to accomplish the proposed 18-month thrust reverser system checks described in Boeing Service Bulletin 747-78A2159, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the test proposed by this AD on U.S. operators is estimated to be $7,200, or $1,200 per airplane, per test cycle.

It would take approximately 544 work hours per airplane, to accomplish the proposed provisional wiring, 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 proposed AD on U.S. operators is estimated to be $195,840, or $32,640 per airplane.

It would take approximately 593 work hours per airplane, to accomplish the proposed sync lock installation, 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 installation proposed by this AD on U.S. operators is estimated to be $213,480, or $35,580 per airplane.

It would take approximately 4 work hours per airplane, to accomplish the proposed functional test of the additional locking system, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the test proposed by this AD on U.S. operators is estimated to be $1,680, or $240 per airplane, per test cycle.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the 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.