Originally Posted by
Joejosh999
Is there an airspeed input component to MCAS ?
737 MAX - MCAS
this mentions “at airspeed approaching stall”
I wondered because we know there was likely an UAS situation for ET, so potentially a pitot hardware issue.
If AoA was all that MCAS received , then we’d be looking at possible alpha vane failure as well, therefore we’d have hardware issues with two separate components.
So - could a blocked pitot be another single point of failure? And the AoA was fine?....
MCAS activation requires AOA above an activation level that is a function of Mach number. The dependence on Mach is not particularly significant (i.e., errant Mach would not significantly impact the MCAS activation point). The amount of stabilizer motion that MCAS will command is also a function of Mach number. With Mach less than 0.4 MCAS will move the stabilizer as much as 2.5 degrees if AOA exceeds the activation threshold by many degrees. At cruise Mach number the size of the MCAS stabilizer motion increment is less than 1/3rd that at low Mach numbers. The bottom line with regard to the question posed here is that a blocked pitot coupled with healthy AOA data would not cause MCAS to activate unless actual (and thus properly sensed) AOA increased to a level significantly above that for normal operation. If you follow pitch/power guidelines after pitot blockage and detection of unreliable airspeed you will not get MCAS. If you get slow and get to elevated AOA following pitot blockage you are likely to encounter MCAS provide flaps are up and autopilot is not engaged.