AD 2020-21-16 Requires Repetitive Ultrasonic Inspections Of The Upper Wing Skin

The FAA is adopting a new airworthiness directive (AD) for all The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes.

This AD was prompted by a determination that the upper wing skin at engine nacelle points may be subject to undetected cracking. This AD requires repetitive ultrasonic inspections of the upper wing skin at certain engine strut positions for cracking; repetitive detailed and ultrasonic inspections of the strut lower spar fitting, diagonal brace strut end clevis, and diagonal brace wing attach end clevis for cracking; repetitive detailed inspections of lower link fitting at certain engine strut positions for cracking; and applicable on-condition actions. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective January 14, 2021.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to all The Boeing Company Model 747-100, 747-100B, 747-100B SUD, 747-200B, 747-200C, 747-200F, 747-300, 747-400, 747-400D, 747-400F, 747SR, and 747SP series airplanes. The NPRM published in the Federal Register on June 30, 2020 (85 FR 39108).

The NPRM was prompted by a determination that the upper wing skin at engine nacelle points may be subject to undetected cracking. The NPRM proposed to require repetitive ultrasonic inspections of the upper wing skin at certain engine strut positions for cracking; repetitive detailed and ultrasonic inspections of the strut lower spar fitting, diagonal brace strut end clevis, and diagonal brace wing attach end clevis for cracking; repetitive detailed inspections of lower link fitting at certain engine strut positions for cracking; and applicable on-condition actions.

The FAA is issuing this AD to address undetected cracking in the upper wing skin, strut lower spar fitting, or clevis lugs at either end of the diagonal brace and lower link fitting. This condition, if not addressed, could adversely affect the structural integrity of the engine strut and may lead to the separation of the strut to wing box assembly.

FMI: www.regulations.gov