Originally Posted by
Interflug
As far as I understand logic, a 3rd AoA would have allowed the system to run a software algorithm that votes an erroneous AoA sensor input out against the other two. That would have solved EVERYTHING in those two crashes, no?
It would have prevented MCAS from activating in the first place. 346 people would still live. Two airplanes would still fly. And all the other 737 MAX would not have been grounded.
How can you come to the conclusion that it wouldn't have solved anything?
We know by now why Boeing did use only one sensor input: to save money, and keeping the reckless promise, that crews would need no expensive training to fly the plane except minutes with some slideshow on the iPad. In order to do so, they had to downgrade the risk as in case of malfunction not potentially catastrophic, and apparently they did so intentionally, and the FAA was partner in crime.
Triplexing of the A of A vanes could, should have prevented the MCAS system from erroneous operation.
However a DUAL system, with a comparitor could well be the fix. If the AoA sensors disagree the MCAS is disabled and there is a flight deck warning of lack of stall warning, fly the airplane normally to destination then fix it ! Loss of stall warning is, frankly, no big deal for continuing the sector, as there has been an infinitely small number of stalls on commercial airliners.
A Boeing precedent was the rudder ratio system on the 75 and 76, my last aircraft. If we got a rudder ratio failure warning, we flew the airplane normally, being aware that coarse rudder inputs at high speed were to be avoided as fin overload could occur, ( they were never used anyway ! ) No sim training required to deal with that, just knowledge of the system.
In addition I believe the degree of travel of the stab. with MCAS, should be limited as a function of speed such that elevator input could overcome the MCAS commanded travel. After the RAF Valiant, my first 4 jet, tailplane runaway and crash in 1964 , we found we could overcome the runaway stab, just by max elevator input, just.
In addition perhaps the MCAS should be limited to one cycle ONLY. afer all, with the shaker and a single nose down push, just how much more stall warning does a trained crew require before initiating the classic recovery technique, lower the nose til the shaker, vibration and noise, or buffet stops, add power, gently roll wings level. Worked on every jet I have ever flown. Even on the T tailed VC 10 we did not have anything as aggressive as the MCAS system and a stall on a T tailed jet could be a lot more dangerous than on a 737.
Comment based on my Boeing experience of about 6000 command hours on the 737 200 and 300, inc as trainer, and 4000 on the 75 and 76, all brilliant aircraft.