Salute
Water !
Great point about hybrid systems as we see with this plane. I do not normally like big quotes, but need to include to set the stage
Quote:
Originally Posted by
spornrad 
Is there
any remote possibility that software reduces the thumb switch authority on the left, not right, in those conditions (AOA disagree/MCAS activation) ?
Water replies:
since it was the left side that the shaker was active on. We don't really know how the thumb switches operate, at first I thought that they were just switches to a solenoid but it seems more likely that they are just inputs to the fancy two computer/four processor 'black box' that is part of the flight control system. At that point, anything is possible since it is software.
If the data we have thus far on the architecture is close to accurate, then the MCAS software or maybe a switch somewhere that feeds the software or ..... ignores some of the previous model features that disabled some trim functions if the control column was pulled or pushed in opposition to what HAL was commanding.
It's the problem with a hybrid system, and a kludge one at that. The 'bus and military FBW systems give up from the beginning, and admit that the computers read control inputs and then give the pilot all the capability the plane has. The interfaces with the controls and computers are strightforward and easy to troubleshoot. It's also easy to determine whether you have a sensor problem or a stick problem or faulty gear/flap position switch and so forth.
Hate to break the bad news to our old, experienced 737 pilots who were unaware of MCAS and how it was implemented, but this new kid on the block ain't the one you flew 5 years ago. We now have had three documented cases where all the pulleys, levers and cables were not enough to overcome stabilizer trim position due to a kludge hdwe/sfwe "fix" to meet the aerodynamic requirements of the certification requirements. You know? Make the thing act/feel like "real" planes are supposed to act/feel.
Since 1973, we have only had a half dozen or so FBW failures in the F-16 that resulted in loss of the aircraft. They were primarily related to power supply design problems, wiring harness chafing, and in one case the loss of the radome due to a pelican impact that destroyed AoA and other air data sensors ( plane flew for another 8 or 9 minutes using just rate and attitude sensors before the pilot used the nylon let down).
I would also put up the Airbus statistics along with those of that little jet I first flew 40 years ago and the newer ones like the Raptor and Stubby (F-35). And be advised that the Stubby does not even have hydraulic lines to some control surface actuators. They are powered by electric motors or electrically powered hydraulic pumps. Makes for survivability if one of your ailerons is blown off by flak, see?
Gums sends...