Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Final rule.

SUMMARY:

This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 747 series airplanes equipped with General Electric Model CF6-45 or -50 series engines, that requires repetitive inspections and tests of the thrust reverser control and indication system, and corrective actions, if necessary. This amendment also requires installation of a thrust reverser actuation system (TRAS) lock, repetitive functional tests of that installation, and repair, if necessary. Installation of the TRAS lock terminates the repetitive inspections and certain tests. This amendment is prompted by the results of a safety review, which revealed that in-flight deployment of a thrust reverser could result in a significant reduction in airplane controllability. The actions specified by this 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:

Effective August 23, 2000.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of August 23, 2000.

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:

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:

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 747 series airplanes equipped with General Electric Model CF6-45 or -50 series engines was published in the Federal Register on October 27, 1999 (64 FR 57802). That action proposed to require repetitive inspections and tests of the thrust reverser control and indication system, and corrective actions, if necessary. That action also proposed to require installation of a thrust reverser actuation system (TRAS) lock, repetitive functional tests of that installation, and repair, if necessary. Installation of the TRAS lock would terminate the repetitive inspections and certain tests.

Comments

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Support for the Proposed Rule

One commenter supports the proposed rule.

Request To Revise Repetitive Interval in Paragraph (a)

One commenter requests that the interval for the repetitive inspections and tests required by paragraph (a) of the proposed rule be extended from 1,300 flight hours to 1,500 flight hours. The commenter states that Work Package I of Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995 [the service information referenced in paragraph (a) for accomplishment of the inspections and tests] has a repetitive interval of 1,500 flight hours, as specified in the service bulletin. The commenter adds that a 1,400-flight-hour-interval aligns with its “2A” check for the fleet, but the 1,300-flight-hour-interval will require additional downtime and place an undue burden on maintenance personnel. The commenter suggests, as another option, that the interval be changed to, “1,500 flight hours or 450 flight cycles, whichever occurs later.” Another commenter requests that the interval be changed to “1,300 flight hours or 450 flight cycles, whichever occurs later.” Both commenters state that the deterioration of the entire system is based on flight cycles, rather than flight hours.

The FAA partially concurs. The FAA does not concur with the commenters' requests to revise the repetitive inspection interval to add the option of flight cycles. The FAA agrees that deterioration of certain thrust reverser components is related to flight cycles because the thrust reversers are typically operated once per flight, causing wear of the components of the actuation system and the thrust reverser brake. However, deterioration of the majority of thrust reverser components is related to flight hours. For example, deterioration of wiring, seals, and proximity sensors and switches is more commonly due to damage due to vibration, temperature extremes, and exposure to moisture. Such factors are flight-hour dependent. Based on this flight hour dependency, the FAA has determined that the inspection interval will not be revised to add the option of flight cycles.

However, the FAA concurs with the commenters' request to extend the repetitive interval stated in the final rule to 1,500 flight hours. Based on discussions with the manufacturer, the FAA has determined that an extension of the interval for the repetitive inspections and tests required by paragraph (a) of the final rule will not have an adverse affect on fleet safety. Therefore, paragraph (a) of the final rule has been revised accordingly.

Request To Extend Compliance Time in Paragraph (d)

One commenter requests that the compliance time for accomplishment of the modification required by paragraph (d) of the proposed rule be extended from 36 months to 60 months in order to allow the modification to be accomplished during the time of its regularly scheduled “D” check. The commenter states that the major portion of the modification involves installation of wiring provisions, and this installation requires a downtime of 250 hours. Another commenter requests the compliance time be extended to 84 months in order to allow the modification to be accomplished during the time of its regularly scheduled “D” check. The commenter states that the proposed requirement to accomplish the complete modification within 36 months, including all service bulletins, would create added problems instead of solutions. The commenter notes that the complete modification would require approximately 1,850 man hours to accomplish, and requests the extension to 84 months so airplanes will not be removed from service.

The FAA partially concurs with the commenters' requests. The FAA concurs that the compliance time for accomplishment of the modification required by paragraph (d) of the final rule may be extended beyond 36 months. Based on information supplied by the commenters and the manufacturer, the FAA acknowledges that a compliance time of 48 months corresponds more closely to the operators' normal maintenance schedules. The FAA has determined that this extension will not adversely affect safety. However, the FAA has concluded that a compliance time of 48 months represents the maximum interval in which the affected airplanes could continue to operate without compromising safety. Paragraph (d) of the final rule has been revised to require accomplishment of the modification within 48 months after the effective date of this AD.

Request To Remove Mandatory Terminating Action in Paragraph (d)

One commenter disagrees with the mandatory requirement to incorporate a TRAS lock as specified in paragraph (d) of the proposed rule. The commenter states that an equivalent level of safety is achieved by accomplishing the thrust reverser health checks at the intervals specified in Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995, including Notice of Status Change 747-78A2160 NSC 1, dated June 8, 1995. The commenter cites fleet statistics that Model 747 series airplanes have flown over 47,212,499 hours to date without any corresponding thrust reverser deployments that have impacted the safety of flight. The commenter further states that the events which triggered regulatory action happened due to thrust reverser deployment of a Model 767 series airplane having two engines and subsequent controllability problems. The commenter also states that there is insufficient documentation from the manufacturer for troubleshooting and correcting operational problems with the TRAS lock. Additionally, there were no adverse operational trends indicated that would impact safety of flight of the Model 747 series airplane; therefore, incorporation of the additional TRAS lock is not justified.

The FAA does not concur with the commenter's request. The FAA recognizes that in-flight thrust reverser deployments have occurred on Model 747 series airplanes in 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 such a deployment. The manufacturer acknowledges that, in the event of thrust reverser deployment during high-speed climb using high engine power, or during cruise, these airplanes may not be controllable.

Although the commenter states that there were no adverse operational trends that would impact safety of flight, the safety analyses performed by the manufacturer and reviewed by the FAA has not established that the risks for uncommanded thrust reverser deployment during critical flight conditions are low enough to prevent a thrust-reverser-related incident during the fleet operation of the Model 747 series airplane. This AD addresses an unsafe condition identified as deployment of a thrust reverser during flight, and requires the installation of an additional thrust reverser system locking feature to correct that unsafe condition. The periodic inspections and tests (thrust reverser health checks) contained in paragraphs (a) and (b) of this AD are a means of verifying proper operation of the thrust reverser components. The FAA has determined that the terminating action required by paragraph (d) of this AD is necessary because the repetitive inspections and tests do not provide an adequate level of safety for the remainder of the life of the fleet of Model 747 series airplanes. Regarding the insufficiency of documentation from the manufacturer, the FAA has been advised by the manufacturer that additional documentation is being developed. No change to the final rule is necessary in this regard.

Comment on Repetitive Inspection Interval in Paragraph (e)

One commenter does not fully agree with the repetitive inspection interval required by paragraph (e) of the proposed rule, “since limited data is available.” The commenter makes no specific request for a change to the proposed rule.

The FAA infers that the commenter is requesting an extension of the repetitive inspection interval for the functional test required by paragraph (e) of the final rule. The FAA does not concur with the commenter's request. In developing an appropriate repetitive interval for this action, the FAA considered not only the degree of urgency associated with addressing the subject unsafe condition, but accomplishment of the required repetitive functional test within an interval of time that parallels normal scheduled maintenance for the majority of affected operators. However, under the provisions of paragraph (h) of the final rule, the FAA may approve requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. No change to the final rule is necessary in this regard.

Request To Revise Cost Impact Estimate

One commenter asserts that the proposed rule underestimates the work hours required to accomplish the proposed installation of the TRAS lock. The commenter states that, based upon feedback from operators that have installed the TRAS lock, approximately 1,850 work hours per airplane is needed for accomplishment of the installation; these hours include all pre-requisite service bulletins. The commenter also notes that it uses third party labor and does not agree that $60 per work hour is the industry average labor rate. The commenter estimates that $100 per work hour is more realistic. Using these figures, the commenter estimates its costs for the proposed installation as $185,000 per airplane, or $4,070,000 for its entire fleet. The commenter adds that it would take an additional 40 work hours per airplane to accomplish the proposed repetitive inspections and tests of the overpressure shutoff valve electrical connectors, the flexible shafts, the directional pilot valves, and the microswitch packs, which equates to $4,000 per airplane. The proposed rule estimates 11 work hours for accomplishment of these repetitive inspections and tests.

The FAA infers that the commenter is requesting that the cost impact information in the final rule be revised to reflect the estimate derived from operator feedback. The FAA does not concur with the commenter's request. The cost impact information in AD rulemaking actions describes only the “direct” costs of the specific actions required by this AD. The number of work hours necessary to accomplish the required actions was provided to the FAA by the manufacturer based on the best data available to date. This number represents the time necessary to perform only the actions actually required by this AD. The FAA recognizes that, in accomplishing the requirements of any AD, operators may incur “incidental” costs in addition to the “direct” costs. The cost analysis in AD rulemaking actions, however, typically does not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. Because incidental costs may vary significantly from operator to operator, they are almost impossible to calculate. Therefore, no change to the final rule is necessary.

Conclusion

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.

Cost Impact

There are approximately 138 airplanes of the affected design in the worldwide fleet. The FAA estimates that 27 airplanes of U.S. registry will be affected by this AD.

It will take approximately 12 work hours per airplane to accomplish the inspections and tests of the thrust reverser stow/deploy switches, the bullnose seals, and the airmotor brakes, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these repetitive inspections and tests required by this AD on U.S. operators is estimated to be $19,440, or $720 per airplane, per inspection and test cycle.

It will take approximately 11 work hours per airplane to accomplish the inspections and tests of the overpressure shutoff valve electrical connectors, the flexible shafts, the directional pilot valves, and the microswitch packs, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of these repetitive inspections and tests required by this AD on U.S. operators is estimated to be $17,820, or $660 per airplane, per inspection and test cycle.

It will take approximately 791 work hours per airplane to accomplish the installation of TRAS locks, at an average labor rate of $60 per work hour. Required parts will be provided at no cost by the airplane manufacturer. Based on these figures, the cost impact of the installation required by this AD on U.S. operators is estimated to be $1,281,420, or $47,460 per airplane.

This cost impact figure does not reflect the cost of the modifications described in the service bulletins listed in paragraph I.K.1.h. of Boeing Service Bulletin 747-78-2150, Revision 1, that are required to be accomplished prior to, or concurrently with, the installation of the TRAS lock. (The cost impact figure does reflect the cost of the modifications described in the service bulletins listed in paragraph I.K.1.j. of the service bulletin that are also required to be accomplished prior to, or concurrently with, the installation of the TRAS lock.) Since some operators may have accomplished certain modifications on some or all of the airplanes in its fleet, while other operators may not have accomplished any of the modifications on any of the airplanes in its fleet, the FAA is unable to provide a reasonable estimate of the cost of accomplishing the terminating actions described in the service bulletins listed in paragraph I.K.1.h. of Boeing Service Bulletin 747-78-2150.

It will take approximately 4 work hours per airplane to accomplish the functional test of the TRAS lock, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the repetitive functional tests required by this AD on U.S. operators is estimated to be $6,480, 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 adopted herein will not have a substantial direct effect 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, it is determined that this final rule does not have federalism implications under Executive Order 13132.

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 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.

2. Section 39.13 is amended by adding the following new airworthiness directive:

2000-14-11 Boeing: Amendment 39-11821. Docket 99-NM-64-AD.

Applicability: Model 747 series airplanes; certificated in any category; equipped with General Electric Model CF6-45 or -50 series engines.

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) 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, which could result in inadvertent deployment of a thrust reverser during flight, and consequent reduced controllability of the airplane, accomplish the following:

Repetitive Inspections and Tests

Note 2:

For the purposes of this AD, a detailed visual inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

(a) Within 90 days after the effective date of this AD, perform the applicable detailed visual inspections and tests to verify proper operation of the thrust reverser stow/deploy switches, the bullnose seals, and the airmotor brake on each engine, in accordance with Work Package I of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995, including Notice of Status Change 747-78A2160 NSC 1, dated June 8, 1995. Repeat the applicable inspections and tests thereafter at intervals not to exceed 1,500 flight hours, until accomplishment of paragraph (d) of this AD.

(b) Within 6 months after the effective date of this AD, perform the applicable detailed visual inspections and tests to verify proper operation of the overpressure shutoff valve electrical connectors, the flexible shafts, the directional pilot valve, and the microswitch pack for each engine, in accordance with Work Package II of the Accomplishment Instructions of Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995, including Notice of Status Change 747-78A2160 NSC 1, dated June 8, 1995. Repeat the applicable inspections and tests thereafter at intervals not to exceed 18 months, until accomplishment of paragraph (d) of this AD.

Corrective Actions

(c) If any of the inspections and tests required by paragraphs (a) and (b) of this AD cannot be successfully performed, or if any discrepancy is detected during the inspections and tests, accomplish paragraphs (c)(1) or (c)(2) of this AD, as applicable.

(1) Prior to further flight, repair in accordance with Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995. Additionally, prior to further flight, any failed inspection or test required by paragraph (a) or (b) of this AD must be repeated and successfully accomplished.

(2) Accomplish both paragraphs (c)(2)(i) and (c)(2)(ii) of this AD.

(i) Prior to further flight, deactivate the associated thrust reverser in accordance with Section 78-1 of Boeing Document D6-33391, “Boeing 747-100/-200/-300/SP Dispatch Deviations Procedures Guide,” Revision 22, dated January 30, 1998. No more than one thrust reverser on any airplane may be deactivated under the provisions of this paragraph.

Note 3:

The airplane may be operated in accordance with the provisions and limitations specified in the operator's FAA-approved Minimum Equipment List (MEL), provided that no more than one thrust reverser on the airplane is inoperative.

(ii) Within 10 days after deactivation of any thrust reverser in accordance with paragraph (c)(2)(i) of this AD, the affected thrust reverser must be repaired in accordance with Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995. Additionally, prior to further flight, any failed inspection or test required by paragraph (a) or (b) of this AD must be repeated and successfully accomplished; once such inspections and tests have been successfully accomplished, the thrust reverser may then be reactivated.

Modification

(d) Within 48 months after the effective date of this AD, install a thrust reverser actuation system (TRAS) lock on each thrust reverser half of each engine, in accordance with Boeing Service Bulletin 747-78-2150, Revision 1, dated July 2, 1998. All of the modifications described in the service bulletins listed in paragraphs I.K.1.h. and I.K.1.j. of Boeing Service Bulletin 747-78-2150, Revision 1, must be accomplished, as applicable, in accordance with those service bulletins, prior to, or concurrently with, the accomplishment of the installation of the TRAS lock. Accomplishment of these actions constitutes terminating action for the repetitive inspections required by paragraphs (a) and (b) of this AD.

Note 4:

Accomplishment of the installation specified in Boeing Service Bulletin 747-78-2150, dated March 20, 1997, is acceptable for compliance with the installation required by paragraph (d) of this AD.

Functional Tests

(e) Within 3,000 flight hours after accomplishing the modification required by paragraph (d) of this AD, or within 1,000 flight hours after the effective date of this AD, whichever occurs later, perform a functional test of the TRAS lock on each reverser half, in accordance with Chapter 78-34-00 of the Boeing 747 Maintenance Manual, dated April 25, 1998.

Corrective Actions

(1) If no discrepancy is detected, repeat the functional test thereafter at intervals not to exceed 3,000 flight hours.

(2) If any discrepancy is detected, prior to further flight, repair in accordance with the procedures specified in the Boeing 747 Maintenance Manual. Additionally, prior to further flight, the functional test must be successfully accomplished. Repeat the functional test thereafter at intervals not to exceed 3,000 flight hours.

Spares

(f) If, after incorporation of the modification required by paragraph (d) of this AD on any airplane, it becomes necessary to install a thrust reverser assembly that does not have the TRAS locks installed, dispatch of the airplane is allowed in accordance with the provisions and limitations specified in the operator's FAA-approved MEL, provided that the thrust reverser assembly that does not have the TRAS locks installed is deactivated in accordance with Section 78-1 of Boeing Document D6-33391, “Boeing 747-100/-200/-300/SP Dispatch Deviations Procedures Guide,” Revision 22, dated January 30, 1998. No more than one thrust reverser on any airplane may be deactivated under the provisions of this paragraph. Within 10 days after deactivation of the thrust reverser, install a thrust reverser assembly that has the TRAS locks installed and reactivate the thrust reverser.

(g) If, prior to incorporation of the modification required by paragraph (d) of this AD on any airplane, it becomes necessary to install a thrust reverser assembly that has the TRAS locks installed, dispatch of the airplane is allowed in accordance with the provisions and limitations specified in the operator's FAA-approved MEL, provided that the thrust reverser assembly that has the TRAS locks installed is deactivated in accordance with Section 78-1 of Boeing Document D6-33391, “Boeing 747-100/-200/-300/SP Dispatch Deviations Procedures Guide,” Revision 22, dated January 30, 1998. No more than one thrust reverser on any airplane may be deactivated under the provisions of this paragraph. Within 10 days after deactivation of the thrust reverser, install a thrust reverser assembly that does not have the TRAS locks installed and reactivate the thrust reverser.

Alternative Methods of Compliance

(h) 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 5:

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.

Incorporation by Reference

(j) Except as provided by paragraphs (c)(2)(i), (e), (e)(2), (f), and (g) of this AD, the actions shall be done in accordance with Boeing Alert Service Bulletin 747-78A2160, dated May 4, 1995, including Notice of Status Change 747-78A2160 NSC 1, dated June 8, 1995; and Boeing Service Bulletin 747-78-2150, Revision 1, dated July 2, 1998. 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.

(k) This amendment becomes effective on August 23, 2000.