Originally Posted by
737 Driver
I hear what you're saying, but let me try this again with a simple example.
To be certifiable (and more to my way of thinking, cleared for dispatch) the 737 needs two functioning Inertial Reference Units (IRU). During the flight, let's say one of the IRU's fail. At this point, the aircraft is no longer "certifiable." However, I'm already in the air, so I pull out the appropriate non-normal checklist (which is quite involved), and let's say I am unable to reset the unit. I will then throw a switch to put both sides on a single IRU and continue to destination under certain additional restrictions. Once the plane is on the ground, it will stay on the ground until the faulty IRU is fixed or replaced. The same logic can be applied to numerous aircraft systems, not just the MCAS.
Every system on the aircraft is subject to failure, and some of those failures will put the aircraft out of its certifiable limit. The manufacturer does not eliminate those systems, but rather they develop non-normal procedures to deal with the failure until the aircraft is on the ground and the system can be repaired. This is the way it has been done in aviation since before I took my first flight.
There are certain components (like the wing) that really do fall in a fail-safe category, and they necessarily meet a much a higher standard. MCAS is not one of those items.
Yes I hear you, but.
You have two functioning IRU's and with one going U/S, you are left with one IRU - the aircraft will function happily with one and there are no parameters of flight that will change. This is redundancy two "required" only one needed. Same with numerous of items like computers, one goes u/s the aircraft operates the same.
MCAS has no redundancy, and if there is a failure of MCAS the flight characteristics do change in certain areas of the envelope. You just will not know how abruptly or placid this change might be until you find yourself there (that may never happen just like an engine failure after take-off) or even amount of change v/s speed. What is the difference in a turn? will it try roll you also?
It is a bit like the flap selector braking off in your hand, no second handle. But the big difference is you know how the aircraft will fly regardless of the setting the handle broke. Chances are you had to do a flap-less landing during your original training - but I doubt for a broken handle! but you practice it at some stage.
Considering this all happens close to the stall and in manual flying condition. A condition almost prohibited at some airlines these days, the very least we expect is that the pilots have trained and practices for these known change of characteristics. But we all know that is not a consideration to be had.