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, that requires an inspection of the flap drive transmission of the trailing edge flaps at positions 2 and 7 to determine if a discrepant torque brake is installed; and corrective action, if necessary. The action specified by this AD are intended to prevent damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap, which could result in flap asymmetry and consequent reduced controllability of the airplane. This action is intended to address the identified unsafe condition.

DATES:

Effective December 31, 2001.

The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of December 31, 2001.

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:

Barbara Mudrovich, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2983; 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 747 series airplanes was published in the Federal Register on May 14, 2001 (66 FR 24304). That action proposed to require an inspection of the flap drive transmission of the trailing edge flaps at positions 2 and 7 to determine if a wound-spring torque brake is installed; and corrective action, if necessary.

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. The Air Transport Association of America, on behalf of its members, states that two commenters agree with the intent of the proposal, but recommend certain changes. These recommendations and additional requests are described in the following paragraphs.

Request To Extend the Compliance Time in Paragraph (a)

A number of commenters request an extension to the proposed compliance time of 6,000 flight hours in paragraph (a) of the proposed AD. These comments and the rationale for requesting such an extension are described in the following paragraphs.

• One commenter states that 6,000 flight hours would fall short of its average C-check, which is usually at 7,500 flight hours. A compliance time of 10,000 flight hours would be more appropriate.
• One commenter states that 6,000 flight hours would require accomplishment of the work at another repair facility, which would put the airplane out of service for at least 1 month. In addition, modification of its fleet of 12 affected airplanes is estimated at 2 to 3 years. In light of this, the commenter recommends a compliance time of 3 years.
• Two commenters recommend that the requirements of the proposed AD be accomplished at a D-check interval. Both commenters are concerned about the availability of spare parts within the proposed compliance time.

The first commenter recommends a compliance time of between 5 and 8 years (25,000 to 38,000 flight hours) for several reasons. Over a 30-year period, none of its Model 747 series airplanes have experienced the unsafe condition cited in the proposed AD (i.e., damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap). It is not aware of any incidents related to such a condition anywhere in the world. In light of this, it considers that such a compliance time is unwarranted and unrealistic. In addition, the manufacturer recommended that the proposed actions be accomplished at the earliest convenient maintenance opportunity, which is more realistic.

The second commenter states that a large number of components and special maintenance schedules would be required to accomplish the proposed actions within 6,000 flight hours. The commenter recommends that the FAA consider how the costs of accomplishing the required actions would affect operators worldwide, and suggests a compliance time of 5 years.

• One commenter contends that the turnaround time required to accomplish the proposed inspection and corrective actions would exceed 6,000 flight hours. In addition, the affected airplanes would need to be transported to a specific repair station because of the test equipment available at that facility. The commenter recommends extending the compliance time to 10,000 flight hours so that the proposed actions could be accomplished during regular maintenance schedules.
• One commenter suggests an 18-month compliance time instead of 6,000 flight hours. The commenter notes that the proposed work could be best accomplished during a C-check maintenance schedule, which coincides with an 18-month compliance time. In addition, all of its Model 747 series airplanes are on an 18-month flight cycle. During that period, a Model 747-200 series airplane accumulates about 6,000 flight hours; however, a Model 747-400 series airplane can accumulate up to 7,000 flight hours. Because flaps typically are used only during climb and descent, flap transmissions are more dependent on flight cycles than flight hours. Therefore, 18 months would provide an equivalent level of safety because actual use of the flap transmission, by cycles, is less on Model 747-400 series airplanes than on Model 747-200 series airplanes. For these reasons, the commenter suggests that the compliance time be revised to “Within 6,000 flight hours or 18 months after the effective date of this AD, whichever is later.”
• One commenter, the manufacturer, states that 6,000 flight hours would be unduly restrictive, with an unjustified impact on airline operations. It suggests scheduling the rework during a D-check, and recommends extending the compliance time to 3 years or 15,000 flight hours, whichever occurs later. The commenter also requests an extension of the proposed compliance time so that it could buy “seed” transmissions that will be required by the operators for their replacement program. This extension would avoid creating an undue burden.

The FAA partially concurs with the commenters' requests, and has determined that the compliance time can be extended somewhat. We point out that the “Differences” paragraph in the proposed AD is not included in the final rule, so no change to that paragraph is necessary. However, we have extended the compliance time somewhat in paragraph (a) of the final rule.

Our intent in developing an appropriate compliance time for the inspections and corrective actions was that the proposed actions be conducted during a regularly scheduled maintenance visit for the majority of the affected fleet. We also intended that the proposed actions be accomplished when the airplanes are located at a facility where special equipment and trained personnel are readily available. Based on the information provided by the commenters, we now recognize that a compliance time of within 18 months or 7,500 flight hours after the effective date of this AD, whichever occurs later, corresponds more closely to the interval that represents most of the affected operators' normal maintenance schedules. This extension will allow operators to schedule the required actions during a convenient maintenance opportunity, and will not adversely affect safety. Paragraph (a) of the final rule is revised accordingly.

Request To Revise Compliance Time in Paragraph (a)(2)(ii)

One commenter requests revising the compliance time in paragraph (a)(ii), which is cited as (a)(2)(ii) in the proposed AD. The commenter considers that, given the level of the hazard posed to the fleet by the torque brake discrepancy, requiring replacement of the torque brake “before further flight” is not warranted. Instead, the proposed AD should allow operators to accomplish the corrective action at a convenient maintenance opportunity. The FAA infers that the commenter is requesting that we revise paragraph (a)(2)(ii) of this AD to require the corrective action within 18 months or 7,500 flight hours after the effective date of this AD, instead of “before further flight.”

The FAA concurs with the commenter's request. The extended compliance time in paragraph (a) of this AD should allow sufficient time for operators to accomplish the rework or replacement action specified in paragraph (a)(2)(ii) at a convenient maintenance opportunity. However, in the final rule we have revised paragraph (a)(2)(ii) to require such action “within the compliance time required by paragraph (a) of this AD,” instead of “before further flight.”

Request To Clarify the Rework or Replacement Action

One commenter requests a revision to the “Explanation of Relevant Service Information” paragraph in the proposed AD. The AD should clarify that operators have the option of either replacing the transmission with a new, improved transmission or reworking the existing transmission by replacing the torque brake with a new or reworked torque brake.

The FAA partially concurs with the commenter's request. Although the “Explanation of Relevant Service Information” paragraph is not included in the final rule, we agree that the replacement and rework action should be revised. In response, we have revised paragraph (a)(2)(ii) in the final rule to require operators to either replace the transmission with a new, improved transmission or rework the existing transmission by replacing the torque brake with a new or reworked torque brake per the service bulletin.

Request To Revise the Applicability

One commenter states that “an Information Notice (IN) made available for 747-27-2374 (IN 01)” was issued June 1, 2000, to clarify that Model 747SP series airplanes are excluded from the effectivity. The notice lists 10 Model 747SP series airplanes by line number and variable number. In addition, those same airplanes are excluded from the effectivity of Boeing Service Bulletin 747-27-2374. The FAA infers that the commenter is suggesting that we revise the applicability of the proposed AD to reflect the exclusion of these airplanes.

The FAA concurs that the applicability of this AD should be changed. We agree that Model 747SP series airplanes should be excluded from the applicability of this AD, and have determined that further clarification of the applicability is necessary. We point out that the applicability of the proposed AD references Boeing Service Bulletin 747-27-2374, dated November 18, 1999, as the appropriate source of service information for determining the affected Model 747 series airplanes. We have revised the applicability of the final rule to include line numbers 0001 through 1207, and to exclude the airplane having line number 1174 and Model 747SP series airplanes.

Request To Correct the Torque Brake References in the Proposed AD

One commenter requests that all references to “wound-spring” torque brakes be removed from the proposed AD. That type of brake is not used in the rework or replacement actions required by the proposed AD.

The FAA concurs. We have removed all references to “wound-spring” torque brakes in the final rule, and have clarified that the “Belleville” spring design is the discrepant torque brake.

Request To Resolve Parts Discrepancies

One commenter states that the Boeing and Moog service bulletins list different part numbers for the flap drive transmission and torque brake installed on Model 747 series airplanes. Any such discrepancies should be resolved before the final rule is issued.

The FAA concurs that any parts discrepancies should be resolved before issuance of the final rule. However, we point out that the parts references included in the Boeing and Moog service bulletins are correct, and that the incorrect parts references were included in the proposed AD. After contacting Boeing, we were informed that it had contacted United to explain that the discrepant torque brake is a “Belleville” spring design, not a “wound-spring” design as cited in the proposed AD. This clarification resolved the commenter's confusion. We have removed all references to the wound-spring torque brake from the final rule, and clarified that the Belleville spring design is the discrepant torque brake.

Request To Revise the Cost Estimate

One commenter states that only 1 hour for the inspection was estimated in the cost impact information in the proposed NPRM to determine whether the affected transmissions are installed on an airplane. The cost of removal, overhaul, and reinstallation of the transmission is not included, and the service bulletin estimates 50 hours per airplane for the associated costs. The FAA infers that the commenter considers that the cost estimate in the proposed AD is too low.

The FAA partially concurs with the commenter. However, we do not agree with the cost estimate of 50 hours specified by the service bulletin for the removal, overhaul, and reinstallation of transmissions. We point out that the estimate in the service bulletin included the action required to replace or rework the torque brake in positions 2, 4, 5, and 7. However, the proposed AD only requires rework or replacement action for positions 2 and 7. As indicated in the preamble of this AD, the economic analysis is limited only to the cost of actions actually required by the rule and does not include the costs of on-condition actions, such as the rework or replacement action specified in paragraph (a)(2)(ii) of the NPRM. However, in this case we have included the on-condition action. These costs include a total of 32 hours per airplane for accomplishing the replacement or rework action for transmission positions 2 and 7 (10 hours for the replacement and 6 hours for the rework). We also have included an estimate of $12,942 for parts. The final rule is revised accordingly.

Request To Reduce the Compliance Time

The Civil Aviation Authority (CAA), which is the airworthiness authority of the United Kingdom, requests reducing the compliance time for the inspection and corrective action if a discrepant part is found installed on the airplane. The CAA considers that the proposed 6,000 flight hours for the inspection is excessively long. It recommends full accomplishment of the inspection and corrective action within 3,000 flight hours, which is approximately 1 year for most operators. In addition, operators should have the discretion of accomplishing corrective action within the recommended total timeframe of 3,000 flight hours.

The FAA does not concur with the need for a shorter compliance time, although operators are always permitted to accomplish the requirements of an AD at a time earlier than that specified as the compliance time. As described earlier, we have determined that it is necessary to somewhat extend the compliance time in paragraphs (a) and (a)(2)(ii) of the final rule to require accomplishment of the actions within 18 months or 7,500 flight hours. We consider such an extension appropriate in consideration of the safety implications, practical aspects of accomplishing the work during regular maintenance periods, and availability of required parts. Therefore, a reduction to the compliance time in paragraph (a) of the final rule would not be warranted.

Request To Correct Paragraph References

One commenter states that, in paragraph (a) of the proposed AD, paragraphs (a)(3) and (a)(4) do not exist. The FAA concurs and has deleted those two paragraph references in paragraph (a) of the final rule.

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 1,181 Model 747 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 263 airplanes of U.S. registry will be affected by this AD.

It will take approximately 1 work hour per airplane to accomplish the inspection, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the required inspection on U.S. operators is estimated to be $15,780, or $60 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

If an operator is required to accomplish the replacement or rework action, it will take approximately 32 work hours per airplane to accomplish such action, at an average labor rate of $60 per work hour. Required parts will cost approximately $12,942 per airplane. Based on these figures, the cost impact of the required replacement or rework is estimated to be $14,862 per airplane.

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:

2001-23-13 Boeing: Amendment 39-12512. Docket 2000-NM-350-AD.

Applicability: Model 747 series airplanes, line numbers 0001 through 1207, certificated in any category; excluding those airplanes having line number 1174 and Model 747SP series airplanes.

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 (c) 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 prevent damage to the flap system, adjacent systems, or structural components; or excessive skew of the trailing edge flap; which could result in flap asymmetry and consequent reduced controllability of the airplane, accomplish the following:

Part Verification/Replacement/Modification

(a) Within 18 months or 7,500 flight hours after the effective date of this AD, whichever occurs later: Inspect the flap drive transmission of the trailing edge flaps at positions 2 and 7 to determine if a discrepant (“Belleville” spring design) torque brake is installed in the transmission, by verifying the transmission part number, per Boeing Service Bulletin 747-27-2374, dated November 18, 1999. Then do the actions specified in paragraphs (a)(1) and (a)(2) of this AD, as applicable.

(1) If the part number of the flap drive transmission shows that no discrepant torque brake is installed, no further action is required by this AD.

(2) If the part number of the flap drive transmission shows that a discrepant torque brake may be installed, within the compliance time required by paragraph (a) of this AD: Inspect the part number of the torque brake to verify whether it is a discrepant torque brake, per the Accomplishment Instructions of the service bulletin.

(i) If the part number of the torque brake shows that it is not a discrepant torque brake, no further action is required by this AD.

(ii) If the part number of the torque brake shows that it is a discrepant torque brake: Within the compliance time required by paragraph (a) of this AD either replace the transmission with a new, improved transmission or rework the existing transmission by replacing the torque brake with a new or reworked torque brake having the part number specified in the service bulletin; per the Accomplishment Instructions of the service bulletin.

Spares

(b) As of the effective date of this AD, no person shall install on any airplane any transmission or torque brake assembly identified in the “Existing Part Number” column of Paragraph 2.E. of Boeing Service Bulletin 747-27-2374, dated November 18, 1999.

Alternative Methods of Compliance

(c) 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. 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 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 Permit

(d) 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

(e) The actions shall be done in accordance with Boeing Service Bulletin 747-27-2374, dated November 18, 1999. 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.

Effective Date

(f) This amendment becomes effective on December 31, 2001.