Airworthiness Directives: The Boeing Company Airplanes

Airworthiness Directives; The Boeing Company Airplanes

Supplementary Information

Background

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to certain The Boeing Company Model 757-200, 757-200CB, and 757-300 airplanes. The NPRM published in the Federal Register on July 21, 2023 (88 FR 47090). The NPRM was prompted by cracks on both sides of the airplane at certain stringers. In the NPRM, the FAA proposed to require an inspection or a maintenance records check for existing liner holes at certain stringers, and applicable on-condition actions. The FAA is issuing this AD to address liner holes that could create a stress concentration around the hole and lead to cracks, which could result in the inability of a structural element to sustain limit load and could adversely affect the structural integrity of the airplane.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from the Air Line Pilots Association, International, who supported the NPRM without change, and additional comments from Aviation Partners Boeing (APB), Boeing, Delta Air Lines, FedEx, and United Airlines. The following presents the comments received on the NPRM and the FAA's response to each comment.

Request to Clarify Location of Crack Findings

Boeing requested that the SUMMARY section of the NPRM be revised to clarify the location of the cracks by replacing the phrase "at certain stringers" with "in the STA 1640 frame web between S-14 and S-15" in two places. Boeing stated that cracks were not detected at the stringer locations, but rather in the frame web between S-14 and S-15.

The FAA concurs with the change and has revised this final rule accordingly.

Request To Clarify Applicable On-Condition Actions

Boeing requested a revision to the NPRM section "Related Service Information Under 1 CFR part 51" to clarify that all on-condition actions depend on the airplane configuration and may include a combination of the actions.

The FAA concurs with the request and has revised this final rule accordingly.

Request To Clarify Required Actions

Paragraph (e) of the proposed AD stated that the AD would address "unplugged liner holes" that could create a stress concentration around "the unplugged hole" and lead to cracks. Boeing requested that the word "unplugged" be removed in both locations. Boeing stated that although the primary concern is unplugged liner holes, the proposed AD would also require actions for certain plugged holes.

The FAA agrees with the request and has changed paragraph (e) of this AD accordingly.

Request To Change Grouping for Certain Airplanes

FedEx stated that all its airplanes affected by the NPRM are Model 757-200 airplanes, and all of these airplanes are currently considered to be Group 1 airplanes, as defined by Boeing Alert Requirements Bulletin 757-53A0120 RB, dated January 17, 2022. FedEx added that its Model 757-200 airplanes were converted to a configuration similar to Boeing Model 757-200SF airplanes (special freighter airplanes with supplemental type certificate (STC) ST00916WI-D) per VT Mobile Aerospace Engineering STC ST03562AT, and therefore its airplanes are no longer configured as passenger airplanes. Because the inspection areas for its airplanes have been modified by STC ST03562AT, FedEx stated that the inspection areas specified for Group 1 airplanes are no longer applicable. FedEx therefore requested that Group 1 airplanes modified by STC ST03562AT be considered Group 3 airplanes, and required to follow all inspections, methods, and compliance times for Group 3 airplanes. FedEx requested this change to avoid the need for an alternative method of compliance (AMOC) for its airplanes when the AD becomes effective.

The FAA agrees that airplanes modified in accordance with STC ST03562AT are no longer Group 1 airplanes, as identified in Boeing Alert Requirements Bulletin 757-53A0120 RB, dated January 17, 2022, and are now Group 3. Paragraph (h)(4) of this AD has been added to specify that Group 1 airplanes that have been converted from a passenger to freighter configuration with STC ST03562AT must do the applicable actions specified for Group 3 airplanes.

Request To Extend Compliance Time

FedEx requested an extension of the initial compliance time to 3,000 flight cycles for actions in Tables 13 through 16 of Boeing Alert Requirements Bulletin 757-53A0120 RB, dated January 17, 2022. FedEx reported that not all of its airplanes will be scheduled for a heavy maintenance visit within the proposed compliance time, and that a 3,000-flight-cycle compliance time would match the Model 757-200SF heavy maintenance schedule. FedEx added that any compliance time requirement sooner than 3,000 flight cycles would force FedEx to schedule airplanes at inopportune times and locations, and would become an even bigger burden to repair any cracking found during the inspections.

The FAA does not agree to change the compliance time. In developing an appropriate compliance time for this action, the FAA considered the recommendations of the manufacturer, the urgency associated with the subject unsafe condition, and the practical aspect of compliance with the AD within a period of time that corresponds to the normal scheduled maintenance for most affected operators. In consideration of these items, the FAA determined that the compliance time, as proposed, will ensure an acceptable level of safety. The FAA has not changed this AD as a result of this comment. However, under the provisions of paragraph (i) of this AD, the FAA will consider requests for approval of alternative compliance times if sufficient data are submitted to substantiate that the change would provide an acceptable level of safety.

Request To Clarify Compliance Times for Airplanes With STC

Delta reported that it operates a number of Boeing Model 757 airplanes with STC ST01518SE installed but without winglets-a configuration approved under STC ST01518SE. Delta noted that paragraph (h)(3) of the proposed AD did not address this configuration. Delta requested that the proposed AD be revised to clarify whether the reduced compliance time specified in paragraph (h)(3) of this AD applies only to airplanes with winglets installed.

The FAA provides the following clarification. A compliance time for airplanes with STC ST01518SE but without winglets has not been evaluated; therefore, that compliance-time requirement applies to all configurations with the STC ST01518SE modification. For clarification, paragraph (h)(3) of this AD has been revised to specify that the reduced compliance time applies to airplanes modified in accordance STC ST01518SE, with or without blended or scimitar blended winglets installed. However, as specified in paragraph (i) of this AD, the FAA will consider requests for approval of alternative compliance times if sufficient data are submitted to substantiate that the change would provide an acceptable level of safety.

Request To Require Different Service Information

APB requested that the proposed AD be revised to require using Aviation Partners Boeing Service Bulletin AP757-53-004, Revision 1, dated February 15, 2023, for airplanes on which APB blended or scimitar blended winglets are installed by STC ST01518SE. APB provided no justification for this request.

Delta requested that paragraph (h)(3) of the proposed AD be revised, for airplanes with STC ST01518SE, to provide the less restrictive compliance times and methods than those specified in the proposed AD by using Aviation Partners Boeing Service Bulletin AP757-53-004, Revision 1, dated February 15, 2023. Delta stated that the conservative compliance times and repeat intervals specified in paragraph (h)(3) of the proposed AD would impose a great operational burden on Delta. Delta reported that it would be unable to accomplish the inspection in a regularly scheduled check environment within the proposed 1,000-flight-cycle compliance time. Delta added that the subject inspections require significant access procedures, which would result in extended unscheduled ground time, and could similarly affect all operators. Delta stated that APB, in its comments on the NPRM, reported that APB Service Bulletin AP757-53-004, Revision 1, dated February 15, 2023, had been independently reviewed by a designated engineering representative (DER) and recommended for FAA approval.

The FAA disagrees with the requests. The FAA has not reviewed nor approved the APB service bulletin. And given the urgency of the identified unsafe condition, the FAA has determined that delaying this AD while this service bulletin is reviewed and approved would be inappropriate. However, under the provisions of paragraph (i) of this AD, the FAA will consider requests for approval of alternative actions and compliance times if sufficient data are submitted to substantiate that the change would provide an acceptable level of safety. The FAA has not changed this AD as a result of this comment.

Conclusion

The FAA reviewed the relevant data, considered the comments received, and determined that air safety requires adopting this AD as proposed. Accordingly, the FAA is issuing this AD to address the unsafe condition on these products. 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.

Related Service Information Under 1 CFR Part 51

The FAA reviewed Boeing Alert Requirements Bulletin 757-53A0120 RB, dated January 17, 2022. This service information specifies procedures for a general visual inspection or maintenance records check of the STA 1640 fuselage frame web between S-14 and S-15, left and right sides, for an existing liner hole, and applicable on-condition actions. Depending on the airplane configuration, on-condition actions include repetitive surface high frequency eddy current (HFEC) inspections for cracks of the web around the fastener (plug), zero-timing the liner hole, plugging the liner hole, repetitive open-hole HFEC inspections of the web for cracks, and crack repair, or some combination of these actions. 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 .

Costs of Compliance

The FAA estimates that this AD affects 419 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 on-condition actions that would be required based on the results of the inspection. The agency has no way of determining the number of aircraft that might need these on-condition actions:

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

Authority for This Rulemaking

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.

Regulatory Findings

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.

The Amendment

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

Part 39 Airworthiness Directives