Originally Posted by
LandIT
If MCAS is so necessary because of the engine cowling moment in certain attitudes, wouldn't it be better to have a third AOA sensor to enable voting in the system. The bigger Boeing's and AB's have more than 2. The 737 is and is going to continue to be among the most numerous planes in the sky. Why not ensure it is as safe as them. I don't accept that saving a relatively small amount of money on a smaller airplane or quoting failures in the per billion hours is really valid when the larger planes have it, obviously for a good reason. There are far more 737's flying, far more takeoffs and landings making for just as much overall risk as the 777's and 787's (assuming more AOA's were provided for greater passenger capacity).
The B737 series is a mostly safe and reliable aircraft, with limited levels of automation. To my knowledge no B737 has crashed (other than the MAX MCAS incidents) solely because of a single isolated AOA failure. AOA is not even a primary flight indicator, as shown by the fact that many airlines declined to fit it.
Trying to fix a faulty MCAS system by adding a third AOA sensor would not be a simple exercise. The necessary design, testing, certification, maintenance and type training changes could take years.
MCAS is not so vital that it justifies rewiring large parts of the aircraft. It only adresses a regulatory issue of pilot yoke elevator feedback in the high AOA part of the manual flight regime.
It is deeply ironic that the issue MCAS was designed to cater for was never flight critical, and might never have occurred during the lifetime of the aircraft. Instead the fix ended up killing hundreds of people.