AD 2021-07-09 Requires Repetitive Inspections Of All TADD Material

The FAA is superseding Airworthiness Directive (AD) 2007-07-03, which applied to certain 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.

AD 2007-07-03 required repetitive tests to detect hot air leaking from the trim air diffuser ducts or sidewall riser duct assemblies (collectively referred to as TADDs), related investigative actions, and corrective actions if necessary. AD 2007-07-03 also provided an optional terminating action for the repetitive tests. This AD requires repetitive inspections of all TADD material for damage and applicable oncondition actions.

This AD was prompted by reports that high temperature composite material TADDs installed as specified in AD 2007-07-03 have also failed. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective May 12, 2021.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2007-07-03, Amendment 39-15003 (72 FR 14395, March 28, 2007) (AD 2007-07-03). AD 2007-07-03 applied to certain 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 September 22, 2020 (85 FR 59451). The NPRM was prompted by reports of sealant deteriorating on the outside of the center wing fuel tank and analysis showing that sealant may deteriorate inside the tank due to excess heat from TADDs.

The NPRM was also prompted by reports indicating that the high temperature composite material TADDs installed as specified in AD 2007-07-03 have also failed. The NPRM proposed to require repetitive inspections of all TADD material for damage and applicable on-condition actions. The FAA is issuing this AD to address potential hot air leakage from original fiberglass fabric material or high temperature composite material TADDs that can cause damage to the center wing fuel tank secondary fuel barrier coating and primary sealant, which can cause fuel leakage into an ignition zone, possibly resulting in a fire or explosion.

FMI: www.regulations.gov