AD 2020-11-12 Ensures Adequate Shielding Of The Underlying Wiring From The Electromagnetic Effects Of HIRF

The FAA is adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737-8 and 737-9 airplanes.

This AD was prompted by a report that certain exterior fairing panels on the top of the engine nacelle and strut (the thumbnail fairing and mid strut fairing panels) may not have the quality of electrical bonding necessary to ensure adequate shielding of the underlying wiring from the electromagnetic effects of high intensity radiated fields (HIRF), which could potentially lead to a dual-engine power loss event and/or display of hazardously misleading primary propulsion parameters. This AD requires a detailed inspection of the thumbnail fairing panels and mid strut fairing panels for excessive rework of the metallic (aluminum foil) inner surface layer, replacement of any excessively reworked panels, and modification of the thumbnail fairing assembly to ensure adequate bonding. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective July 30, 2020.

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 certain The Boeing Company Model 737-8 and 737-9 airplanes. The NPRM published in the Federal Register on February 26, 2020 (85 FR 11000). The NPRM was prompted by a report that certain exterior fairing panels on the top of the engine nacelle and strut (the thumbnail fairing and mid strut fairing panels) may not have the quality of electrical bonding necessary to ensure adequate shielding of the underlying wiring from the electromagnetic effects of HIRF, which could potentially lead to a dual-engine power loss event and/or display of hazardously misleading primary propulsion parameters. The NPRM proposed to require a detailed inspection of the thumbnail fairing panels and mid strut fairing panels for excessive rework of the metallic (aluminum foil) inner surface layer, replacement of any excessively reworked panels, and modification of the thumbnail fairing assembly to ensure adequate bonding.

The FAA is issuing this AD to address this condition, which could result in a forced off-airport landing or excessive flightcrew workload.

FMI: www.regulations.gov