Originally Posted by
Tomaski
As far as the test you refer to, it was a different malfunction than the one presented to the accident crews, particularly as it presented a runaway trim with the A/P engaged so no one was getting direct feedback through the controls. Even though the FAA reports that this malfunction has never been seen in actual operation, it deserves to be fixed because you never know when the stars will line up against you.
The malfunction also involved flipping a bit to fool the FCC computer into thinking MCAS was active, which disabled the control column cut-out switches from stopping the runaway trim. One or more of the other bit flips must also have prevented the FCC computer from recognizing that MET was being used because use of MET should have reset the MCAS bit to "off," which should have re-enabled the control column cut-out switches (unless the pilots were told to recover without MET). As I wrote before, and tried to explain again (my comment wasn't posted), the likelihood of a five-bit error flipping the five specific bits needed to create the simulator scenario is beyond astronomically small. If the chance of the stars (or in this case neutrons) lining up, over the lifetime of the type, is less than one in a trillion, would you still say that it deserves to be fixed (even though the chances of messing up the fix is probably a lot greater than that)?
Originally Posted by
Tomaski
The current FCC architecture relies very heavily on the pilots detecting a malfuntion, and if the airlines aren't going to properly train for this role then the architecture needs to be fixed.
The pilots of both accident aircraft detected a malfunction. Detecting the malfunction with enough time to take corrective action wasn't the problem in either flight. The Lion Air crew successfully countered with nose-up trim for about 6 minutes. Nobody knows why they stopped or why they didn't turn electric trim off (or why they apparently advanced the throttles in the final dive). The Ethiopian Airlines crew detected the malfunction but failed to follow the AD (I also believe ET302 was overweight, further complicating the crew's situation).