AD 2022-06-07

This AD is effective May 31, 2022.

The Director of the Federal Register approved the incorporation by reference of a certain publication listed in this AD as of May 31, 2022.

For service information identified in this final rule, contact Boeing Commercial Airplanes, Attention: Contractual & Data Services (C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; telephone 562-797-1717; internet https://www.myboeingfleet.com. You may view this service information at the FAA, Airworthiness Products Section, Operational Safety Branch, 2200 South 216th St., Des Moines, WA. For information on the availability of this material at the FAA, call 206-231-3195. It is also available at https://www.regulations.gov by searching for and locating Docket No. FAA-2021-0828.

Luis Cortez-Muniz, Aerospace Engineer, Airframe Section, FAA, Seattle ACO Branch, 2200 South 216th St., Des Moines, WA 98198; phone and fax: (206) 231-3958; email: Luis.A.Cortez-Muniz@faa.gov.

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2016-09-01, Amendment 39-18499 (81 FR 26109, May 2, 2016) (AD 2016-09-01). AD 2016-09-01 applied to certain The Boeing Company Model 777-200 and -300 series airplanes. The NPRM published in the Federal Register on October 14, 2021 (86 FR 57078). The NPRM was prompted by reports of fatigue cracking of the forward outer chord of the STA 2370 pivot bulkhead, and the determination that the compliance times need to be reduced, post-modification inspections must be done, and the inspections areas need to be expanded due to additional cracking found prior to the inspection times required by AD 2016-09-01. In the NPRM, the FAA proposed to retain certain requirements of AD 2016-09-01. The NPRM also proposed to require doing repetitive detailed and HFEC inspections of the longeron fitting and, for certain airplanes, the bulkhead assembly structure, for any cracking and doing all applicable on-condition actions. The FAA is issuing this AD to address fatigue cracking of the outer flanges of the left and right side forward outer chords of the STA 2370 pivot bulkhead, which could result in a severed forward outer chord and consequent loss of horizontal stabilizer control.

The FAA received comments from an anonymous commenter, The Air Line Pilots Association, International (ALPA), and United Airlines who supported the NPRM without change.

The FAA received additional comments from three commenters, including Air France, Boeing, and an individual. The following presents the comments received on the NPRM and the FAA's response to each comment.

Air France requested that Boeing and the FAA increase the inspection threshold to 1,000 flight cycles in the proposed AD. Air France stated that the proposed AD specifies that operators accomplish the nondestructive testing inspection within 500 flight cycles and that this threshold is not compatible in case of findings; this drives an operator to ground the airplane for a long period of time if a corrective action needs to be accomplished before further flight. Air France commented that a minimum of 300 man-hours are required to accomplish the corrective actions specified in Boeing Service Bulletin 777-53-0076 [which is referenced in Boeing Alert Service Bulletin 777-53A0075, Revision 2, dated February 22, 2021].

Air France stated that its request allows operators to plan a C-check maintenance visit during a time when a repair or the terminating action specified in Boeing Service Bulletin 777-53-0076 can be performed without disturbing airplane operations.

The FAA disagrees with the commenter's request. As specified in Boeing Alert Service Bulletin 777-53A0075, Revision 2, dated February 22, 2021, the compliance time of 500 flight cycles is a grace period and is only applicable when the airplane exceeds the inspection threshold. In addition, in developing an appropriate compliance time, the FAA coordinated with the manufacturer to provide a compliance time that maintains an acceptable level of safety. However, under the provisions of paragraph (i) of this AD, the FAA will consider requests for approval of an extension of the compliance time, if sufficient data are submitted to substantiate that the change would provide an acceptable level of safety. The FAA has not changed this final rule in this regard.

An individual requested that Boeing increase the frequency of its testing in addition to exploring additional NDE techniques ( e.g., ultrasonic testing) for identifying early indication of high cycle fatigue. The commenter stated that when looking at probability of failure, Boeing has identified at least 32 instances of cracking under the current inspection frequency; however, one of the biggest issues with the high cyclic fatigue cracking is that it is self-identifying. The individual commented that while there are various NDE tools and techniques that can be used to identify cracks once they have started to propagate, it is incredibly difficult to identify degraded conditions prior to fracture propagation. The commenter concluded that the probability of a crack developing unnoticed under the current inspection frequency should be considered moderate to high.

While the FAA acknowledges the commenter's concern, this AD already incorporates reduced compliance times for the repetitive detailed and HFEC inspections, adds new inspection areas for any cracking and also adds repetitive post-modification inspections to the previous requirements of AD 2016-09-01. The determination of the mitigating actions and compliance times were coordinated with the manufacturer and determined to provide an appropriate interval of time while maintaining an acceptable level of safety. The FAA has not changed this AD in this regard.

Boeing requested that the SUMMARY section of the NPRM be revised to change the words, “for certain airplanes, the bulkhead assembly structure” to “for post-repair and post-modification inspections, the bulkhead assembly structure.” Boeing stated that the requested change is to clarify that the inspection of the bulkhead assembly structure is only required for airplanes that have accomplished the small crack repair option using Boeing Alert Service Bulletin 777-53A0075, Revision 1, dated December 14, 2015, or the modification using Boeing Service Bulletin 777-53-0076.

The FAA agrees that the proposed wording provides clarity and has revised the SUMMARY section of this AD accordingly.

Boeing requested that the FAA remove the words “of the” in the first sentence under the “Proposed AD Requirements in this NPRM” paragraph in the NPRM. Boeing stated that the sentence should be revised from “retain certain of the requirements of AD 2016-09-01,” to “retain certain requirements of AD 2016-09-01.”

The FAA acknowledges that “of the” in the first sentence under the “Proposed AD Requirements in this NPRM” paragraph in the NPRM should be removed; however, that paragraph is not carried over into this final rule.

Boeing requested that the FAA revise paragraph (h)(1) of the proposed AD, which specifies using the effective date of this AD rather than the Revision 2 date of the service information, to remove the reference to the “Effectivity” paragraph and the Condition columns in the “Compliance” paragraph. Boeing stated that the phrase “the Revision 2 date of this Service Bulletin” is not used in those locations of the service information.

The FAA agrees with the commenter's request and has revised paragraph (h)(1) of this AD accordingly.

The FAA reviewed the relevant data, considered any comments received, and determined that air safety requires adopting this AD as proposed. Except for minor editorial changes, and any other changes described previously, this AD is adopted as proposed in the NPRM. None of the changes will increase the economic burden on any operator.

The FAA reviewed Boeing Alert Service Bulletin 777-53A0075, Revision 2, dated February 22, 2021. This service information specifies procedures for, depending on configuration, doing repetitive detailed and HFEC inspections of the STA 2370 pivot bulkhead forward outer chord and the longeron fitting for any cracking; doing repetitive post-repair inspections of the pivot bulkhead forward outer chord, longeron fitting, and bulkhead assembly structure for any cracking; doing repetitive post-modification inspections of the pivot bulkhead forward outer chord, longeron fitting, and bulkhead assembly structure for any cracking; and doing all applicable on-condition actions. On-condition actions include modifying the left and right forward outer chords and upper splice angles, and repair.

This service information is reasonably available because the interested parties have access to it through their normal course of business or by the means identified in ADDRESSES.

The FAA estimates that this AD affects 63 airplanes of U.S. registry. The FAA estimates the following costs to comply with this AD:

The FAA estimates the following costs to do any necessary modifications that would be required based on the results of the inspection. The FAA has no way of determining the number of aircraft that might need this modification:

The FAA has received no definitive data on which to base the cost estimates for the repairs specified in this AD.

The FAA has included all known costs in its cost estimate. According to the manufacturer, however, all of the costs of this AD may be covered under warranty, thereby reducing the cost impact on affected operators.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII: Aviation Programs, describes in more detail the scope of the Agency's authority.

The FAA is issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701: General requirements. Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

This AD will not have federalism implications under Executive Order 13132. This AD 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.

For the reasons discussed above, I certify that this AD:

(1) Is not a “significant regulatory action” under Executive Order 12866,

(2) Will not affect intrastate aviation in Alaska, 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.

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:

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

2. The FAA amends § 39.13 by:

a. Removing Airworthiness Directive (AD) 2016-09-01, Amendment 39-18499 (81 FR 26109, May 2, 2016); and

b. Adding the following new AD: