The Federal Aviation Administration on Thursday issued a directive requiring airlines to perform regular maintenance checks of the flight control software on Boeing’s 737 MAX and to periodically test the operation of cutoff switches used by pilots in the event of failure. of the system.
All the MAXs currently in flight have undergone these checks before the planes return to the sky after 21 months of immobilization of the world fleet.
Boeing sent the details of the maintenance regime to all of the MAX’s air operators in December, just before the first planes returned to service.
The FAA said in a statement that all MAX operators in the United States have already included these inspections in their maintenance programs and that it has issued the directive “to emphasize the importance of these inspections to other international regulators and operators. outside the United States “.
Boeing has said it “fully supports” the directive, which affects approximately 72 MAX registered in the United States and 389 jets worldwide.
New flight control software on the MAX that was not on previous 737 models – known as the Maneuver Characteristics Augmentation System (MCAS) – accidentally activated during the two fatal flights in 2018 and 2019 which killed 346 people in Indonesia and Ethiopia.
Boeing updated this software to correct its faulty design and the FAA recertified it in November, approving the MAX for return to service.
The new FAA directive requires a check of the entire flight control software system every 6,000 flight hours, which could be roughly every two years for a jet that is used extensively on domestic routes. .
System testing is simple and can be scheduled during routine maintenance. It is performed using electronic test equipment built into the aircraft.
An FAA official explained that he checks the health of the entire automated flight control system, “including the MCAS.”
The directive states that regular checks are deemed necessary due to the possibility of a “latent failure” of an element of the flight control system, that is, a failure which may not be immediately apparent but might show up later.
The FAA official said the directive requires relatively frequent inspections because “if it’s potentially latent, you become conservative.”
The directive also requires airline maintenance personnel to verify that pilot control console switches that shut off power to the horizontal tail moving surfaces are functioning properly.
In the event of an MCAS malfunction, the pilots would use this pair of cutoff switches to prevent the system from pushing the nose of the aircraft down.
A newly mandated third maintenance check requires technicians to periodically check an autopilot cut-off switch as well as the ground electrical path that controls the moving part of the horizontal tail – known as the stabilizer – and therefore the pitch of the l ‘plane.