Stabilizer trim limit switches limit the up and down travel of the horizontal stabilizer leading edge during either normal electric actuator trimming operation or autopilot trimming operation of the horizontal stabilizer.The lever operated microswitches are mounted in a vertical row on brackets on the stabilizer jackscrew compartment aft bulkhead.
AMM
From the Blufer book,with flaps UP main electrim trim authority is 3.95 to 14...in other words if the stabilizer is trimmed by MCAS past 3.95,the pilot wouldnt be able to use main electrim trim to trim it back up.I dont read those graphs too well...what setting did they have just prior to the dive?
I believe that if you trim it down manually to 0 units you can then trim it back up using main electric but....
No mention in the report which channel MCAS uses.....PRI or BU or both.
FCEng confirmed it uses same channel as STS which would presumably be B/U on the Max.If so why the order to cut both PRI and BU?That must be Boeing trying again not to confuse average pilots...ie just perform the existing NNC(RUNAWAY) and you ll disable MCAS.However,is MCAS disabled by selecting B/U
alone to cutout?
No mention of EFS in the report either which presumably was activated and would have made the pilots job even harder.
Of course its just a preliminary report and they wont get into that....and of course none of the above is really relevant as the only way to recover was to disable the trim not oppose it.However,if the tug of war had lasted a little bit longer they may have finally clued in....what a shame they didnt keep the flaps and land from circuit height.Simulator instructors are ever so keen to teach pilots to climb to MSA,perform the NNC,and take your time.....oh the irony.They love their procedure and sometimes forget
about airmanship.This plane could have been landed safely from pattern altitude by performing the first 3 memory items of the UAS NNC and using basic thrust/attitude combinations for downwind to short final which any average pilot already knows.Dont prolong a flight in an aircraft that is dangerously unairworthy.It was day VMC at a sea level airport....
Final report will have to discuss this startle factor and how it can affect crews(even experienced ones) when they face a)loss of SA b)reality/perception mismatch.One definition of it is
startle effect can be defined as an uncontrollable, automatic reflex that is elicited by exposure to a sudden, intense event that violates a pilot’s expectations
FAA
The intense physiological response(ie heart rate/release of adrenalin etc) to something unexpected/untrained can impair rational thought and decision-making.The
activation of alarms can really exacerbate the confusion and tendency to "freeze",especially so if there are multiple
alarms and they are conflicting.Birgenair is a classic case.An experienced commander on takeoff puts his aircraft in a dangerously ANU attitude during a simple UAS event(single side) with simultaneous activation of stick shaker and overspeed alarms.In hindsight.it beggars belief.
Did this crew freeze?They responded to ATC,they called for a block altitude,they reselected flaps once the deadly AND trim began.They opposed the MCAS with ANU trim inputs a dozen times or more.They showed "fight" not "flight".But in "fight" mode the pilots actions are often instinctual not always analytical.As the Boeing engineer said,Lionair's maintrol woeful failures meant that the problem aircraft was repeatedly
put back into service until it found "a crew that couldnt handle the situation".
Now of course Lionair program a simulator season of UAS and RUNAWAY stabilizer training sessions....too late now isnt it...