The Lion Air Boeing 737 MAX crash in October revealed that the Maneuvering Characteristics Augmentation System (MCAS) software installed on the aircraft could push the plane’s nose down as a result of faulty Angle of Attack readings.
While pilots can disable this system, many weren’t aware of the way that it worked, having only received limited training as they transitioned from earlier generation 737s to flying the MAX.
Boeing has unveiled software changes that should make erroneously engaging the system less likely, and less challenging for pilots if it ever does happen. They are awaiting certification for the changes after “hundreds of hours of analysis, laboratory testing, verification in a simulator and two test flights, including an in-flight certification test with Federal Aviation Administration representatives on board as observers.”
- The system will compare data from both sensors to avoid inaccurate readings instead of relying on one sensor at a time. If inputs are off by more than five and a half degrees, MCAS and the speed trip system will be inhibited for the rest of the flight.
- MCAS will drop the plane’s nose only once each time it detects a high angle of attack instead of doing so persistently.
- Nose down movement will be easier to overcome by pilots in order “to override MCAS input with sufficient manoeuvring ability that the aircraft can still climb.”
- Better training on the differences between earlier generation 737s and the MAX.
Given that the result of failure of an angle of attack sensor can be hazardous relying on a single input seems like it was a questionable decision. This software update is badly needed, even though every 737 MAX pilot is certainly well aware at this point how to disengage the MCAS system — as well as under what circumstances they’d want to do so.