Originally Posted by
derjodel
To ensure that an erroneous signal from a failed single AOA sensor does not prevent continued safe flight and landing, ...
Your quick summary was very helpful. I tried to squeeze it down, then adding more from the FAA proposal.
Like this:
- AOA DISAGREE alert on PFD installed by default (activates when more than 10 degrees difference for more than 10 seconds)
- Inputs of both AoA sensors processed as source for activating MCAS
- AoA disagree exceeding a calculated threshold will inop STS/MCAS for the remainder of the flight
(treshold as function of magnitude of disagreement between AoA sensors and rate of change of the values)
This will activate an indication to crew (STS/MCAS off)
- Only one MCAS activation per high AoA event
- The magnitude of MCAS stab command will be limited so that the plane thereafter can be controlled by elevator only to climp/level/descend.
The magnitude varies according to parameters such as the airplane’s altitude and airspeed
- Not only MCAS related checklist changes
- Wiring Changes to comply with current regulation
Maintenance:
- AoA prope system test once befor RTS
- MEL affected, new MMEL
That completes my overview.
Details I digged out:
WRT checklist changes:Airspeed Unreliable
Runaway Stabilizer
Stabilizer Trim Inoperative
Speed Trim Fail
Stabilizer Out of Trim
AOA Disagree
ALT Disagree
IAS Disagree
I also found the answer to my question "land next suitable" in a proposed new NNC:
Speed Trim Fail (Required by AD 2020-**-**)
The Speed Trim function and MCAS function are inoperative.
Continue normal operation.
Note: The Speed Trim System will not provide stabilizer trim inputs when
deviating from a trimmed airspeed.
...with the background
(...)To assist the flightcrew in properly responding to such
an occurrence, a non-normal checklist, called the Speed Trim Fail checklist, would be
added to the AFM. This checklist would be used when the STS and MCAS functions are
inoperative, and inform the flightcrew to continue normal operation. (...)
Protection from aerodynamic instability lost? Continue normal! Even in the notes no addressing of approach to stall issues. Wow. But the document states: checklist proposals may be altered as a result of flight evaluation.
Regarding MEL and Flight Control System, this is suggested:
(1) Dispatch is not permitted with both autopilot systems inoperative.
(2) The autopilot disengage aural warning system must be operative for dispatch.
(3) The STAB OUT OF TRIM light must be operative for dispatch.
(4) The speed trim function must be operative for dispatch. NOTE: This requires both FCCs to be operative for dispatch.
(5) The SPEED TRIM FAIL light must be operative for dispatch.
(6) Dispatch is not permitted with both A/P ENGAGE Command (CMD) Switches (A and B) inoperative.
(7) Dispatch is not permitted with both A/P ENGAGE Command (CMD) switch lights inoperative.
(8) Dispatch is not permitted with both autopilot (A/P) disengage lights inoperative. Dispatch may be made with one A/P disengage light inoperative provided the autopilot disengage aural warning system operates normally.
(9) Dispatch is not permitted with both Control Wheel Autopilot Disengage Switches inoperative. Dispatch may be made with one control wheel autopilot disengage switch inoperative provided the following conditions are met. a) Mode Control Panel autopilot DISENGAGE bar operates normally, b) Autopilot is not used below 1,500 feet AGL, and c) Approach minimums do not require use of autopilot.
(10) Both control wheel trim switch systems must be operative for dispatch.