In what some pilots are calling an inconceivable moment in flight operations and training, Boeing recently admitted the existence of the maneuvering characteristics augmentation system (MCAS), an angle of attack related stall prevention system that was unknown to operators of the Boeing 737 Max 8 aircraft, like the one flown last week by a Lion Air crew when it departed Jakarta Indonesia. The Lion Air crew experienced an unexpected nose pitch down shortly after takeoff as the aircraft was passing through 5,000 feet. Unable to recover from the event, all 189 people aboard perished in the crash that followed.
While it’s too early to draw any solid conclusions, there appears to be a circumstantial link between the, until now unknown MCAS and the angle of attack error messages reported early on following the Lion Air accident. The FAA last week issued an emergency airworthiness directive against the 737 Max 8 that said, “erroneously high single angle of attack (AOA) sensor input could result in ‘repeated nose-down trim commands of the horizontal stabilizer,’ which could be from the MCAS,” according to the Aviation Safety Network.
Operators of the 737 Max aircraft wasted no time making clear their feelings about Boeing’s apparent oversight in the release of MCAS information. In a message yesterday, ASN says the Allied Pilots Association (APA), which represents American Airlines Group Inc. pilots, alerted its members … to the MCAS saying “it applies nose down stabilizer in specific conditions when the aircraft nears a stall,” the first time many pilots were made aware of the system’s existence.
The APA said the logic behind MCAS was not mentioned in training or in any other manuals or materials. Safety Committee Chairman Capt. Michaelis stated, “It’s pretty asinine for them [Boeing] to put a system on an airplane and not tell the pilots who are operating the airplane, especially when it deals with flight controls,” according to the ASN.
A Boeing message quoted by the APA said, “the MCAS (Maneuvering Characteristics Augmentation System) is implemented on the 737 MAX to enhance pitch characteristics with flaps UP and at elevated angles of attack. The MCAS function commands nose down stabilizer to enhance pitch characteristics during steep turns with elevated load factors and during flaps up flight at airspeeds approaching stall. MCAS is activated without pilot input and only operates in manual, flaps up flight. The system is designed to allow the flight crew to use column trim switch or stabilizer aisle stand cutout switches to override MCAS input. The function is commanded by the Flight Control computer using input data from sensors and other airplane systems.
A January 2018 report of the new Boeing’s created by the Brazilian ANAC briefly mentions the MCAS, but offers no specific guidelines on its operation. Whether the Lion Air 610 crew had any knowledge of the MCAS’s existence prior to their October 29 takeoff is unknown. Sources said Boeing risk assessment team felt the chances of the MCAS going off in flight were so remote, they felt an explanation of the system was unnecessary
Boeing told Flying through a prepared statement in part, “We are taking every measure to fully understand all aspects of this incident, working closely with the investigating team and all regulatory authorities involved … Safety remains our top priority and is a core value for everyone at Boeing. While we can’t discuss specifics of an on-going investigation, we have provided two updates for our operators around the world that re-emphasize existing procedures for these situations.”
Capt. John Weaks, president of Southwest Airlines Pilots Union (SWAPA) quoted in the Wall Street Journal said, “We’re pissed that Boeing didn’t tell the companies and the pilots didn’t get notice obviously, as well. But what we need now is to make sure there is nothing else Boeing has not told the companies or the pilots.”