Originally Posted by
fizz57
Disagree. May address the issues that caused the latest accident, but contradicts the entire concept of the 737's instrumentation system, and will invalidate the safety calculations on which certification is based, as well as possibly opening the doors to other failure modes.
The 737 instrumentation is a dual-redundant system, comprising two completely separate systems such that in the event of a single failure one completely operational system is still available. With the aid of appropriate disagreement monitors, standby instruments and checklists, pilots are trained to detect and diagnose such failures and take appropriate action.
This system was state-of-the-art at the time the 737 was launched and is still in use in smaller, non-FBW airliners. It is totally adequate for its stated task, that is to provide information to a well-trained human crew. It should never have been allowed to provide inputs to a system that will automatically drive flight control surfaces.
Respectfully, I don't agree with you. The concept of the 737 has been changed dramatically from the original 93' span/94' length, 110K Lbs to the current 117' span/118' length, 195K Lbs. Adding STS, LAM, and now MCAS also contradicts the original B737 instrumentation system. The B737 overhead panel should have been thrown out when the designed the NG, and definitely with the MAX (FYI, DC9 and B717 are the same type rating). Having a switch to deselect a faulty indicator does not open the door to other failure modes. Not having an AOA disagree light as standard is just bad/cheap design (and Boeing agrees, all their MAXes will be retrofitted, and I believe all their more recent designs use 3 AOAs). Not informing crews about MCAS was the wrong thing to do, and not having a checklist for it letting crews re-trim the aircraft to neutral before using the cut-out for MCAS failure (as opposed to regular runaway trim) IMHO was a big mistake, just like certifying MCAS working on one AOA at a time was a big mistake.