MIAMI – On 24 June the Federal Aviation Administration (FAA) has finalized a rule requiring operators to inspect Boeing 737 Max wiring shields for issues that could, in extreme circumstances, cause dual-engine failures or erroneous engine data.

The rule does not relate to the flight control system implicated as a factor contributing to two 737 Max crash incidents where 346 people died: Lion Air Flight 610 on October 29, 2018, and Ethiopian Airlines Flight 302 on March 10, 2019.

Content of the directive

The FAA’s airworthiness directive (AD) requires that the Boeing 737 Max, Max 10 not included, be inspected for wiring shield issues prior to flight.

Boeing 737 Max 8/9 models remain grounded following the crash incidents. Boeing itself addressed the wire-shield issue with a service bulletin released in 2019.

The FAA’s order follows reports that “exterior fairing panels on the top of the engine nacelle and strut may not have the quality of electrical bonding necessary to ensure adequate shielding.”

According to earlier FAA materials such fields are caused by “electromagnetic energy from radar, radio, television and other ground-based, shipborne or airborne radio frequency transmitters”.

According to published reports, workers polishing the carbon composite engine pods ground off some layers of metal foil that are needed to shield wiring. The FAA said any “excessively reworked panels” must be replaced.

Statement from Boeing

Boeing says it “recommended this action in December 2019″ and has been working closely with its customers to ensure the 737 Max’s engine nacelles are fully protected from electrical energy. “We support the FAA’s airworthiness directive, which makes our recommended action mandatory.”

Boeing asked the FAA to require that the inspections be completed before revenue flights, rather than before non-revenue flights, but the FAA declined that request.

Boeing has told the FAA it will cover the cost of the work done to the 737 Max because the aircraft are still under warranty.