Attempting to tamp down pilot concerns about its 737 MAX following the Lion Air crash, Boeing technical representatives met with at least two pilot unions this week. And industry sources say the company is considering a software revision to the airplane’s anti-stall autotrim system.
Lion Air JT610, a 737 MAX with only 800 hours on the airframe, crashed into the Java Sea off Jakarta on Oct. 29, killing all 189 people aboard. The Indonesian National Transportation Safety Committee released a preliminary report this week showing that the crew experienced continuous stick shaker activation shortly after takeoff due to a faulty angle of attack sensor. Because its engines are heavier and mounted farther forward, Boeing equipped MAX airplanes with an autotrim system called MCAS. It’s activated at high angles of attack and automatically applies nose-down trim as an anti-stall protection. Pilot unions have complained that Boeing didn’t document the existence of MCAS—Maneuvering Characteristics Augmentation System—and crews weren’t trained on it.
MCAS hasn’t been implicated in the crash, but the NTSC’s preliminary report showed that it was active during the crash flight and the pilots continually trimmed manually against its nose-down trim input. A previous crew that encountered the same problem addressed it through the standard runaway trim procedure, which is to use the airplane’s two stabilizer trim cutout switches to disable electric pitch trim. All models of the 737 are still equipped with manual trim wheels.
Boeing set up urgent meetings with pilot unions from Southwest and American Airlines, although what was discussed hasn’t been reported. “We were appreciative that Boeing reached out to us,” said Mike Trevino, spokesman for the Southwest Airlines Pilots Association, according to USA Today. A spokesman for the Allied Pilots Association, the American Airlines union, said the organization was looking for the Boeing outreach. “They brought in their A team,” said Dennis Tajer of APA.
At least one airline that operates the MAX, Southwest Airlines, says it’s discussing with Boeing the option of adding an angle-of-attack indication to the MAX’s primary flight display. Currently, the airplane has an AoA disagree flag that warns pilots if the two vane-type AoA sensors are providing inconsistent data. The option may be available on future MAX deliveries. Meanwhile, a report in the Daily Globe and Mail said Boeing may consider software revisions to the MAX, although the details weren’t revealed.