Former Boeing Flight Control Engineer Says Alterations May Have Contributed To Two Accidents

A change in the function of two cockpit switches in Boeing's 737 MAX airplanes may have contributed to accidents in Indonesia and Ethiopia, according to a former Boeing flight control engineer.

Peter Lemme first called the changes into question on his blog, according to The Seattle Times. Lemme said that a change in the functionality of the switches meant pilots were not able to disable the MCAS on the airplane without also disabling the trim switches on the airplane's yoke.

On previous versions of the 737, the autopilot could be disengaged, but the trim controls would have remained active. One switch deactivated the autopilot, while the other disengaged the yoke trim switches. But on the MAX, both switches performed the same function, disabling both the autopilot and the electronic trim.

Boeing said in a statement that pilots have always been trained to flip both switches to deal with a "runaway" stabilizer, and the change to the MAX matched the established procedure. But the company kept both switches "for commonality of the crew interface. Boeing strongly disagrees with any speculation or suggestion that pilots should deviate from these long-established and trained safety procedures,” Boeing said.

While Lemme questions the change that appears to him to be "change for change's sake", aviation consultant Doug Moss, a former commercial airline pilot qualified in Boeing aircraft, told the paper that the procedure needs to be as simple as possible to prevent confusion in an emergency situation. Asking pilots to flip only one switch rather than both could add an unnecessary level of complexity to the procedure.

Boeing is continuing to work on a software update for the MCAS system on the 737 MAX, and the fleet remains grounded worldwide while that issue is addressed.

(Image from file)

FMI: Source report