AD 2021-09-08 Prompted By Manufacturing Design Changes To Certain Metallic Support Panel Assemblies

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 manufacturing design changes to certain metallic support panel assemblies installed in the flight deck, which resulted in insufficient electrical bonding of the panels and consequent insufficient electrical grounding of installed equipment. This AD requires modification of the electrical bonding of these assemblies to provide sufficient electrical grounding for equipment installed in the flight deck. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective April 30, 2021.

Supplementary Information: The FAA has received a report of an electrical bonding and grounding issue that was discovered during testing of a newly manufactured Boeing Model 737-8 airplane. During standard production testing by Boeing, electrical power systems did not perform as expected. Investigation identified insufficient bonding of certain metallic support panel assemblies installed in two areas of the flight deck, which affects the electrical grounding of installed equipment. The reported event occurred prior to delivery of that airplane. Investigation identified design changes to the flight deck support panel assemblies, which affected the dedicated bonding and grounding paths that existed prior to the changes.

The affected areas are the P6 panel assembly, including the mounting tray for the standby power control unit (SPCU), located behind the first officer, and the main instrument panel (MIP) assembly located in front of and between the captain and first officer. The issue affects certain Boeing Model 737-8 and 737-9 airplanes manufactured after the design changes were implemented. All affected in-service airplanes passed all testing prior to delivery, and there have been no reported in-service failures due to this condition. However, without dedicated grounding paths implemented by design, there is a potential for degradation or loss of the existing uncontrolled ground paths on those airplanes over time.

Degradation of bonds essential for the electrical grounding of equipment, if not addressed, could affect the operation of certain systems, including engine ice protection, and result in loss of critical functions and/or multiple simultaneous flight deck effects, which may prevent continued safe flight and landing. The FAA is issuing this AD to address the unsafe condition on these products.

All affected airplanes, both in the U.S. and worldwide, have been removed from service, pending development and implementation of approved corrective action that will address the unsafe condition.

FMI: www.regulations.gov