Tests on Boeing’s grounded 737 Max have revealed a new safety risk unrelated to two fatal crashes that led to the grounding of the aircraft, and US regulators are ordering the company to make additional design changes.
The Federal Aviation Administration discovered that data processing by a flight computer on the jetliner could cause the plane to dive in a way that pilots had difficulty recovering from in simulator tests, according to two people familiar with the finding who asked not to be named to discuss it.
“The FAA recently found a potential risk that Boeing must mitigate,” the agency said in an emailed statement on Wednesday. The statement didn’t provide any specifics.
While the issue didn’t involve the Maneuvering Characteristics Augmentation System linked to the two fatal accidents since October that killed 346 people, it could produce an uncommanded dive similar to what occurred in the crashes, according to one of the people, who wasn’t authorised to speak about the matter.
Gordon Johndroe, a Boeing spokesman, said the company agreed with the FAA finding and was addressing the issue as well as a broader software redesign that’s been underway for eight months.
“Addressing this condition will reduce pilot workload” by making it easier to respond to an uncommanded stabilizer motion, Johndroe said. “The safety of our airplanes is Boeing’s highest priority,” he added. “We are working closely with the FAA to safely return the Max to service.”
The 737 Max has been grounded worldwide since March 13, days after the second crash. “The FAA will lift the aircraft’s prohibition order when we deem it is safe to do so,” the FAA said in the statement.
Exercises on a Boeing 737 Max simulator in recent days revealed that pilots might have difficulty responding to the newly identified failure, the person said.
Just as MCAS uses a motor to move a small wing at the tail of the plane to lower the nose, the latest issue could prompt that same wing to move without pilot commands. The tail wing is known as a horizontal stabilizer.
The motor on the stabiliser adjusts up and down movements known as trim. Examining how trim failures occur has been a central part of safety reviews of the plane because it was central to the accidents.
The FAA as well as an independent Technical Advisory Board have been reviewing Boeing’s software fix in multiple sessions in a special Boeing simulator that is designed for engineering reviews.
“We continue to evaluate Boeing’s software modification to the MCAS and we are still developing necessary training requirements,” the agency said in its statement.
Boeing hasn’t presented its final proposed fix to FAA for approval. Before it can do so, it has to conduct a final test flight with FAA pilots.