RE More than one AOA sensor- found and interesting comparison method as used on 787 and ? 777 by using the Inerital system ( GPS etc ) basically igt seems to provide a sensor independent check on several normal flight sensors like pitot tubes etc. Granted 777 and 787 are more closer to FBW, but still retain some backup. 787 calls it the Common Mode
Source can be found by searching on
Introducing the 787
Tom Dodt
Chief Engineer - Air safety Investigation
ISASI september 2011
Pages 39 thru 41
Common Mode Hazards to Pitot-Static sensors
- Mud Daubers
- Icing - Hail - Birds - Taped Static Ports
- Volcanic Ash
- Radome failure
- Pitot covers
- Maintenance errors (pneumatic plumbing)
• 787 new capabilities for protection - Synthetic airspeed
- GPS altitude - Common Mode Monitor
Calculated from angle of attack and inertial data
- AOA – voted dual sensors plus inertial data
- Accurate Coefficient of Lift (CL) - Airplane Mass from FMC - Validated after Takeoff
• Algorithm developed for enhanced stall protection
• Avoid displaying data known to be bad - Loss of valid voted VCAS = Display synthetic airspeed VSYN - Loss of valid voted PSTATIC = Display GPS altitude
So Boeing was well aware of how to compare and how to use a separate ( Inertial-GPS ) system to cross check and eliminate faulty data ...
But it probably cost to much to include on 737MAX to avoid long standing issues-