As Boeing pushed to provide airlines with more information on a background auto trim system on its 737 MAX, the head of one pilot union said it’s not necessary for pilots to know the details of every automatic system on an airliner and that they’re already adequately trained to handle runaway trim abnormals.
The auto trim system is called MCAS and is intended to improve pitch characteristics and stall protection when the aircraft is hand flown at high angles of attack and high load factors. Although it’s not directly implicated in the Oct. 29 crash of a Lion Air 737 MAX into the Java Sea, investigators are examining what role it might have played.
Breaking ranks with two other pilot unions and his own Air Line Pilots Association leadership, Todd Insler, chairman of the United Airlines ALPA unit, questioned why ALPA publicly pushed Boeing to provide more information on the auto trim system, insisting that pilots are already well trained to handle any uncommanded trim events. Unions for Southwest and American Airlines and ALPA’s national leadership have been critical of Boeing for failing to provide pilots with documentation on MCAS as they transitioned to the MAX.
“We’re the only U.S. ALPA operator of the airplane,” Insler told Forbes. “We weren’t consulted by ALPA prior to their putting the letter out.” Insler said although MCAS isn’t specifically described in United training manuals, runaway trim procedures are: “You have to manually take control—that is one of the early things they teach you when you fly jets. The procedure is there in our manual, and we practice this over and over again. The first time I see an adverse event, I want to see it in a simulator, not with 300 people behind me,” Insler said in the Forbes report. In an interview with the Seattle Times, Insler compared automated background systems on airliners to watching television. “I don’t need to know how it works,” he said.
Indonesian investigators revealed flight tracking data that showed Lion Air JT610 flew sharp pitch, vertical speed and altitude excursions before plunging almost directly into the water 11 minutes after taking off from Jakarta. All 189 people aboard were killed. The aircraft had a recent history of unreliable airspeed indications and an angle-of-attack sensor had been replaced prior to the flight. MCAS—Maneuvering Characteristics Augmentation System—relies in part on data from the AoA sensor. If it detects high AoA at high load factors when the airplane is being flown manually with flaps up, it automatically rolls in nose down stabilizer trim at the rate of 0.27 degrees per second to a maximum of 2.5 degrees. If the AoA condition isn’t resolved, the cycle repeats. The 737 has stabilizer trim cutout switches that inhibit electric trim from functioning and pilots are trained to use these as a standard runaway trim response.
Indonesian investigators say they hope to release a preliminary accident report by the end of November. Meanwhile, shortly after the crash, Boeing sent information on MCAS to MAX operators and the FAA followed up with an emergency AD describing failure indications and responses.
