Transport Canada says Boeing must make it possible for pilots to deactivate the stick shaker in 737 MAX aircraft when it’s clearly responding to bad sensor information. The measure is in addition to the software rewrite of the Maneuvering Characteristics Augmentation System (MCAS) that was a factor in the fatal crashed of new MAXes in Ethiopia and Malaysia in 2018 and 2019. As an interim measure, TC wants the MAX manual to include a note on how to pull the circuit breaker for the stick shaker. A proper override would have to be developed and retrofitted later. TC is concerned about the stress and distraction an erroneous stick shaker indication adds in the cockpit during an emergency. In the Ethiopian Airlines crash, the yoke (737s don’t have sticks) shook and banged throughout the six minute flight based on bad data from one of the angle of attack indicators.
The TC requirement is in addition to two demands made by the European Aviation Safety Agency before the aircraft can be recertified. The U.S. Federal Aviation Administration has agreed to make the EASA and TC fixes part of the certification requirements. While MCAS has been fixed to require agreement between two AOAs, EASA wants all systems on the plane that use AOA data to require agreement. It also wants additional redundancy beyond two AOAs. Airbus aircraft have three AOAs. EASA says it wants Boeing to have the same level of redundancy as three AOAs will provide but it can be achieved through an alternative to actually adding a third AOA.