The Federal Aviation Administration has mandated that US airlines perform repeated inspections of aspects of Boeing 737 Max flight control systems.

The airworthiness directive (AD), issued on 16 June, lays out the requirements, which align with instructions Boeing released in December 2020, the FAA states.

“All operators of US-registered 737 Max airplanes have already included these inspections in their maintenance programmes,” adds the agency.

737 Max

Source: AirTeamImages

A Boeing 737 Max

Regulators globally grounded the 737 Max in March 2020 after two crashes, which investigators linked to erroneous activation of the Max’s Maneuvering Characteristics Augmentation System (MCAS).

The FAA’s 16 June AD requires airlines to “revise their existing maintenance programmes to include three additional repetitive inspections”.

Operators must complete “specific electric checks” on aircraft with more than 6,000h of flight “to verify the correct operation of the airplane’s automated flight control system”, the FAA says.

Boeing did not immediately respond to a request for comment.

Specifically, airlines must check aspects of the “digital flight control system”, including those related to aileron and elevator “actuator availability”. They must also check aspects of the stabiliser trim system, including cut-off switches.

The checks will help ensure “the availability of certain flight control system functions through maintenance tests”, and “verify that the functions have not failed,” the FAA says. “A potential latent failure of a flight control system function… if combined with unusual flight manoeuvres or with another flight control system failure, could result in reduced controllability.”

Additionally, the FAA issued a Continued Airworthiness Notifications to the International Community (CANIC) in which it highlights “the importance of these inspections.”

The FAA’s order applies to 72 US-registered aircraft and 389 aircraft globally.