Originally Posted by
MechEngr
I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly. Earlier I wondered how the FGCs used the two inputs and was surprised to see they are bypassed to operate those alarms directly. Perhaps I misread it, but it makes a great deal of sense to push that function as early in the sensor chain as possible to decrease the number of links and the ability to fail.
I do agree that figuring out the desired failure handling is not easy. It has to be one that sorts false inputs from true inputs and tells the pilots what has gone wrong. Still it's been possible to shut down the remaining operating engine when the stress levels get too high, so it's clear that solving this general problem is not easy.
What is clear is that the outcome possible under the previous version will never happen again; that is, there won't be a chance that under an AoA disagree situation that an MCAS or, possibly, even STS correction to trim will be allowed. So now it's shifted to the more esoteric argument about how to automate proper handling of false information that looks exactly like true information. Anyone who comes to the certain solution for that problem will clean up in the stock market.
Your quote "I believe the 737 stick-shaker and stall alert are operated by the ADIRUs directly".
Your information is incorrect:
Two independent, identical stall management yaw damper (SMYD) computers
determine when stall warning is required based upon:
• alpha vane angle of attack outputs
• ADIRU outputs
• anti–ice controls
• wing configurations
• air/ground sensing
• thrust
• FMC outputs.
The SMYD computers provide outputs for all stall warning to include stick shaker
and signals to the pitch limit indicator and airspeed displays and the GPWS
windshear detection and alert.
Two test switches are installed in the aft overhead panel. Pushing either of these
initiates a self–test of the respective stall warning channel. The No.1 activates the
Captain stick shaker, and the No. 2 activates the F/O stick shaker. Either stick
shaker vibrates both columns through column interconnects.
STALL WARNING TEST Switches
Push – on ground with AC power available: each test switch tests its respective
stall management yaw damper (SMYD) computer. No.1 SMYD computer shakes
Captain’s control column, No.2 SMYD computer shakes First Officer’s control
column. Vibrations can be felt on both columns