Originally Posted by
deltafox44
Reducing the speed (or not letting it grow) is an obvious remedy but easier to say afterwards. If they have the stick shaker since the take-off, with a normal airspeed, they may think the fault is on airspeed and apply the procedure to keep N1 at a relatively high value that will accelerate the aircraft beyond controlability limits...
Keep trimming and if the system continuously trims you nose down as you are accelerating know that is the opposite direction of STS and thus incorrect => shut the stabilizer down. First and foremost keep trimming to keep the column forces from building up. The problem of getting progressively more out of time takes 10s of seconds to build up and will stop if you keep trimming. If MCAS decides it is time to put in 10 seconds of nose down trim and you determine after a couple of seconds that it is doing the wrong thing and add your own nose up trim, MCAS will stop until you have been off of the trim for 5 continuous seconds. If all you do is blip the trim once every 5 seconds MCAS won't do anything even if the AOA it is getting is out of whack high! Eventually it is hoped that the crew will decide that the automatic stabilizer is doing far more harm than good and turn if off via the cutout switches.
Oh - did I mention enough times that you should keep trimming?!
I'm not trying to argue that MCAS as currently design is satisfactory, but with the system knowledge that we had before the end of 2018 I was confident that we had an acceptable workaround until improvements could be brought to the fleet.
If it turns out the the Ethiopian accident was the result of the same issues that led to the Lion Air accident our industry has some major soul searching to do.
MCAS appears to have been designed based on three assumptions that I have suggested before:
1. If a pilot trims column force will be trimmed to or near zero.
2. Having the automatic stabilizer control continuously take the airplane away from trim when otherwise flying a relatively steady condition, pilots will recognize that it is not healthy and would shut it down via the stabilizer cutout switches.
3. An errant AOA signal feeding MCAS would be acceptable because of (1) and (2) above.
Lion Air showed us that for the crew the day before the accident assumptions (1) and (2) above were reasonable so when (3) happened they were able to fly home.
- In fact they elected to go on to their destination with the stick shaker rattling the whole way!
Lion Air further showed us that for the pilot on the accident flight assumption (1) above held. He made more than 20 corrections and was able to maintain his apparent target altitude of 5000 feet reasonably well. He did not get to (2) above, but might have had his partner been able to keep up with (1) after transferring control.
The Lion Air accident clearly showed that neither assumption (1) nor (2) held true for the second pilot and thus control was lost as a result of not meeting assumption (3).
737MAX was permitted to continue flying after the data from the Lion Air accident revealed the facts outlined above, through so many PPRUNE pages, and across so many other information outlets including FAA and Boeing communications because an assumption was made that with increased awareness pilots would be able to live up to assumptions (1), (2), and (3) above. I would like to think that most of the pilots flying 737MAX airplanes in February were prepared to live up to these assumptions. If the recently decoded FDR from the Ethiopian accident shows that to be a repeat of the Lion Air event this latest assumption will clearly not have been valid for at least one 737MAX crew.
While the MCAS software update developed after the Lion Air accident that is almost ready to go to the fleet will likely remove reliance on the three MCAS design assumptions listed above and thus would have greatly improved the likelihood of a safe outcome for the Ethiopian event we are left with a huge elephant in the room. After making the planned update we still must address the following:
A. How many other key points in the 737MAX safety story are based on pilot response assumptions that may not be valid?
B. How about other airplane models? Are they deemed safe based on faulty assumptions regarding pilot action?
- For instance, how may current 737 crews (all models) would not respond quickly enough to a classic stabilizer runaway that was not arrested by column cutout (i.e., pulling the column far enough)? I know this is covered in simulator sessions for 737 pilots, but is that enough?
C. Moving forward with the current status and future of commercial aviation have we gotten to the point where basic flying skills and system awareness are so low that we are at risk throughout the whole industry?
D. Can current and future pilot reaction short falls be addressed through training? If so, what kind, how much, and how often?
E. How will we know that we have achieved a sufficient industry wide level of safety?
Hoping to see FDR data from the Ethiopian accident soon. I sure hope someone from the PPRUNE community will find a way to get ahold of it and share it here.