EASA Issues Proposed AD for 737 Max Return to Flight

 - November 24, 2020, 5:54 PM
It may take until mid-January 2021, before Boeing 737 Max airliners can return to service in Europe. (Photo: AIN/David McIntosh)

A proposed airworthiness directive (AD) issued by EASA on November 24 outlines conditions that would allow Boeing’s 737-8 and -9 Max to resume flying in Europe following their worldwide grounding in March 2019. The grounding was the result of two accidents that killed 346 passengers and crew.

Comments on the EASA proposed AD are due 28 days after the proposed AD’s issuance, and EASA expects to finalize the AD in mid-January. A preliminary safety directive issued at the same time also has a 28-day comment period and will apply to non-European airlines with third-country operator authorization flying the Max into EASA member states.

In addition to changes to the airplanes, EASA also is requiring a mandatory pilot training program that will include simulator training, “to ensure that the pilots are familiar with all aspects of the flight control system of the 737 Max and will react appropriately to typical failure scenarios.”

Changes to the airplane mirror the requirements of the FAA and include flight control computer and maneuvering characteristic augmentation system software updates; an update to display an alert to pilots if there is a disagreement between the two angle-of-attack (AoA) sensors; separation of wires from the flight deck to the stabilizer trim motor; flight manual, limitations, and procedures updates “to equip pilots to understand and manage all relevant failure scenarios”; systems and AoA sensor testing; and before carrying passengers, an operational readiness flight.

There are two key differences between the EASA AD and the FAA AD, according to EASA, which said, “EASA explicitly allows flight crews to intervene to stop a stick shaker from continuing to vibrate once it has been erroneously activated by the system, to prevent this distracting the crew.” This presumably is in response to the stick shaker activation that occurred in the two fatal Max accidents, which apparently confused the pilots and did not hamper their ability to control the airplane. The other difference is that EASA won’t allow use of the autopilot for “certain types of high-precision landings,” but that “is expected to be a short-term restriction.”

The FAA and EASA and other regulators agreed that pilots ought to be able to silence nuisance events like the stick shaker if it is activating because of erroneous AoA inputs, to reduce pilot workload. However, the FAA’s system safety analysis and associated functional hazard assessment determined that false stick shaker activation is a “major” failure effect and not a more severe “hazardous” effect. That means in case a major failure effect occurs, the pilots can continue flying safely, so there is no need to switch off the stick shaker. EASA 737 Max operators will have to make it possible for pilots to intervene to stop the stick shaker. The AD would require installing colored caps on the stall warning stick shaker circuit breakers, and the if pilot had to shut off the stick shaker, it would be by pulling the circuit breaker. 

“EASA made clear from the outset that we would conduct our own objective and independent assessment of the 737 Max, working closely with the FAA and Boeing, to make sure that there can be no repeat of these tragic accidents, which touched the lives of so many people,” said EASA executive director Patrick Ky. 

“I am confident that we have left no stone unturned in our assessment of the aircraft with its changed design approach,” he added. “Each time when it may have appeared that problems were resolved, we dug deeper and asked even more questions. The result was a thorough and comprehensive review of how this plane flies and what it is like for a pilot to fly the Max, giving us the assurance that it is now safe to fly. 

“EASA’s review of the 737 MAX began with the MCAS but went far beyond,” Ky said. “We took a decision early on to review the entire flight control system and gradually broadened our assessment to include all aspects of design which could influence how the flight controls operated. This led, for example, to a deeper study of the wiring installation, which resulted in a change that is now also mandated in the Proposed Airworthiness Directive. We also pushed the aircraft to its limits during flight tests, assessed the behavior of the aircraft in failure scenarios, and could confirm that the aircraft is stable and has no tendency to pitch-up even without the MCAS.”