Indonesian aircraft missing off Jakarta

[CONSO]

..... ZZUF
For this MCAS system to work the aircraft needs to "know" when it has reached the particular flight envelope corner. I would expect that inputs such as alpha, alpha rate, bank angle, flap setting, power setting, G, IAS/CAS, possibly CG and others.
So, how did the aircraft think it was in the corner point, just waiting for an alpha signal within the trigger range? Surely not a single failure?
Anyway this is just fantasy.[/QUOTE]


FAA and BA DOES think a single AOA failure can cause MCAS ' failure'

DATE: November 7, 2018
AD #: 2018-23-51
Emergency Airworthiness Directive (AD) 2018-23-51 is sent to owners and operators of The
Boeing Company Model 737-8 and -9 airplanes.
Background
This emergency AD was prompted by analysis performed by the manufacturer showing that if
an erroneously high single angle of attack (AOA) sensor input is received by the flight control
system, there is a potential for repeated nose-down trim commands of the horizontal stabilizer. This
condition, if not addressed, could cause the flight crew to have difficulty controlling the airplane, and
lead to excessive nose-down attitude, significant altitude loss, and possible impact with terrain.

[EDLB]

I think the wording is "there is a potential", not "can". So what else is require to achieve the potential outcome??

The pilots not flipping the cut off switch?

[CONSO]

I think the wording is "there is a potential", not "can". So what else is require to achieve the potential outcome??

legalese hoping to avoid responsibility- IMHO wording really should be " WILL repeat nose down trim for 10 seconds, followed by a 5 second pause, then repeat . . "

as in page 51 of the report

Boeing FlightFlight Crew Operations Manual Bulletin Crew Operations Manual Bulletin number number TBC TBC-19-19
THE FOLLOWING PROCEDURE AND/OR INFORMATION IS EFFECTIVE UPON RECEIPT
Background Information
The Indonesian National Transportation Safety Committee has indicated that
Lion Air flight 610 experienced erroneous AOA data. Boeing would like to call
attention to an AOA failure condition that can occur during manual flight only.
This bulletin directs flight crews to existing procedures to address this condition.
In the event of erroneous AOA data, the pitch trim system can trim the stabilizer
nose down in increments lasting up to 10 seconds. The nose down stabilizer trim
movement can be stopped and reversed with the use of the electric stabilizer trim
switches but may restart 5 seconds after the electric stabilizer trim switches are
released. Repetitive cycles of uncommanded nose down stabilizer continue to
occur unless the stabilizer trim system is deactivated through use of both STAB
TRIM CUTOUT switches in accordance with the existing procedures in the
Runaway Stabilizer NNC. It is possible for the stabilizer to reach the nose down
limit unless the system inputs are counteracted completely by pilot trim inputs
and both STAB TRIM CUTOUT switches are moved to CUTOUT.

[DaveReidUK]

Originally Posted by Bleve

I have often ridden on a flightdeck jumpseat even though I was on the manifest as a passenger.

Yes, hence the bit from my post that you missed out in your quote:

Originally Posted by DaveReidUK

Once the CVR is found, if it emerges that the engineer was in fact in the jumpseat, then that will likely also reveal whether they were either just there as a courtesy, or in an observer/troubleshooting role.

[infrequentflyer789]

Originally Posted by MickG0105

I found the following [...] It details the different operation of the stabilizer trim main electric motor (turns in only one direction and drives the stabilizer trim actuator through two electro-magnetic clutches, one for NU, another for ND) and the autopilot trim system (turns in either direction and drives the stabilizer trim through a single clutch).
[...]
Does anyone know if that described motor/clutch arrangement has been carried on through the NG/MAX line?

based on the bits of AMMs I (unofficially) happen to have, the answer to that appears to be - no. Or more precisely "only some of it". Comparing drawings:



the "autopilot trim servo" is totally missing on the NG. Block diagrams also show both autopilot and main electric trim signals going to the same actuator.

The actuator does seem to be the same with multi-speed single direction drive and dual clutch. A duel between manual electric and auto trim doesn't seem to be possible, but one clutch sticks "on" and the other engages might be possible, then, my guess, the whole lot would jam which would most likely unstick the dodgy clutch fairly rapidly - the not properly disengaged clutch would be the weakest point.

Worth noting that this run-on issue on classics was only in high speed mode, and the trim motor is (should be) in high speed mode only when flaps are down. MCAS is (should be) on only with flaps up, therefore with low speed mode and much less loading on the whole actuator system. Also looking at ADs the binding clutch issue was fixed with a new (actuator) part number, before the NG was in service.

[silverstrata]

Originally Posted by tdracer

Ah, no they are not... The maximum engine ratings on the Max are very similar to the corresponding models of the NG. .

The -400 had 24,000 lb thrust.
The -800 had 27,000 lb thrust.
The max-8 has 28,000 lb thrust.

I call that a steady increase in thrust, with a steady increase in pitch up moment, when applying full power at low speeds. Besides, the Bournemouth incident, where a 737 pitched up to 47 degrees, demonstrated that even the NG series had more thrust-pitch moment than the elevator had aerodynamic pitch moment, when at slow speeds.

Silver

[Maisk Rotum]

Stab trim moves in a direction I don't want or expect. I don't give a toss about what causes it. MCAS or PFM. I'm trained to move the stab trim switches to cutout, pull the handle out and start cranking it so that I bring the aircraft back in trim at the target attitude and adjust the thrust according to the memory items for unreliable airspeed. They were not incapacitated as they were on ATC coms till the end responding to multiple unnecessary calls. It is instructive that the previous crew turned the stab trim switches off and landed safely.

[MickG0105]

Originally Posted by infrequentflyer789

based on the bits of AMMs I (unofficially) happen to have, the answer to that appears to be - no. Or more precisely "only some of it". - the not properly disengaged clutch would be the weakest point.

Very good, thank you for that information.

Originally Posted by infrequentflyer789

Worth noting that this run-on issue on classics was only in high speed mode, and the trim motor is (should be) in high speed mode only when flaps are down. MCAS is (should be) on only with flaps up, therefore with low speed mode and much less loading on the whole actuator system.

My understanding of MCAS is that while it only operates in manual flight with flaps up, it runs the trim nose down at the (faster) flaps down rate of 0.27 units per second. You can see a rate of trim disparity between MCAS trimming down at 0.27 units per second and the slower flaps up commanded main electric trim rate in the FDR data. I think that that is one of the issues with trying to countermand MCAS ND trim with main electric NU trim. If you're not actually checking the resultant trim outcome and just retrimming nose up on an 'equal time' basis MCAS will win the slow war of attrition to get the stab trimmed further and further nose down.

[FrequentSLF]

Originally Posted by Maisk Rotum

Stab trim moves in a direction I don't want or expect. I don't give a toss about what causes it. MCAS or PFM. I'm trained to move the stab trim switches to cutout, pull the handle out and start cranking it so that I bring the aircraft back in trim at the target attitude and adjust the thrust according to the memory items for unreliable airspeed. They were not incapacitated as they were on ATC coms till the end responding to multiple unnecessary calls. It is instructive that the previous crew turned the stab trim switches off and landed safely.

SLF question...
I infer from your post that you are saying that the previous crew was better than the one that (pace to their souls) died in the crash.
An aircraft certification requires that the plane should be flown by an average pilot, who was the average pilot? the one that flown the previous sector or the one the one that was flying the last sector?

[Rananim]

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...

[glad rag]

"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".

Who provided the aircraft maintenance course curriculum?

[phil gollin]

.

I asked this about two weeks ago, saying that by this time (two weeks ago) in a normal thread about these sorts of incidents someone normally chirps up saying that "I tried doing this in a simulator and ....." No response then, how about now ?

Or are the MAX simulators all too busy for pilots to experiment in ?

.

[safetypee]

Thanks td #1827. 'a good idea given previous accident history'.
For those who wish to follow up a philosophical safety theme, the see René Amalberti’s ‘Revisiting safety and human factors paradigms to meet the safety challenges of ultra complex and safe systems.’ Basically be very careful in selecting ‘improvements’ so not to introduce new, unforeseen hazards, particularly the ‘big one’.
https://www.dropbox.com/s/2dpt1o3pix...k2000.pdf?dl=0

slacktide #1828. Previous discussions all noted, but the simplification what could be a complex design change by focusing on lift detracts from the underlying science.
Perhaps td could help with other possible engine related aspects. Larger fan whirl; larger intake airmass momentum drag, Harrier / AV8 Pilots might have a view - translate yaw problems into pitch for the 737. (Didn’t the 777 have a problem in these areas, - or perhaps that was physical fan momentum with engine failure).

[climber314]

Exclusive: Boeing eyes Lion Air crash software upgrade in 6-8 weeks

https://www.reuters.com/article/us-i...-idUSKCN1NZ00S

While plans for the possible fix are not final, Boeing’s software upgrade could block the recently modified anti-stall system, known as MCAS, from continuously running until the plane hits its nose-down limit, the sources said.

The MCAS function would be disabled if the crew counteracted it by trimming or adjusting settings in the opposite direction, according to two people briefed on Boeing’s proposals.

“When the crew makes the adjustment, that would essentially disengage MCAS unless it got new data,” one of the people said.

Southwest Adding AoA Indicators to 737 Max Fleet

https://theaircurrent.com/aviation-s...737-max-fleet/

[Less Hair]

So the automatic system feels the speed is close to some stall but will let you trim even more into that stall?

[aterpster]

Originally Posted by phil gollin

.

I asked this about two weeks ago, saying that by this time (two weeks ago) in a normal thread about these sorts of incidents someone normally chirps up saying that "I tried doing this in a simulator and ....." No response then, how about now ?

Or are the MAX simulators all too busy for pilots to experiment in ?

.

Not sure there are any MAX simulators. Other, perhaps, than at Boeing.

[GarageYears]

Originally Posted by aterpster

Not sure there are any MAX simulators. Other, perhaps, than at Boeing.

There certainly are! The first was delivered to the Boeing Miami Flight Training Center in April 2017 and multiple simulators have followed around the world.
And no, they are not only at Boeing facilities. Air Canada has at least one.

I could probably find a list, but it might take a while.

- GY

[GarageYears]

Originally Posted by GarageYears

There certainly are! The first was delivered to the Boeing Miami Flight Training Center in April 2017 and multiple simulators have followed around the world.
And no, they are not only at Boeing facilities. Air Canada has at least one.

I could probably find a list, but it might take a while.

- GY

OK, there we go, there are currently five Level C/D qualified devices. There are certainly many more in production currently.

- GY

[climber314]

Or Boeing has the ONLY simulator with MCAS functions in Seattle?

The investigation will next head to Seattle and the 737-MAX engineering simulator where investigators will attempt to exercises to better understand what happened.

If Boeing didn't think it was important enough to mention MCAS in the QRH, why would they provide the code for it in a multi-million dollar simulator? Textron/TRU has 737 MAX Simulators in Miami as of 4/2017, but I would be shocked if they could replicate this flight. I don't think you get extra play time @ > $1,000/hour?

[GarageYears]

Originally Posted by climber314

Or Boeing has the ONLY simulator with MCAS functions in Seattle?

The investigation will next head to Seattle and the 737-MAX engineering simulator where investigators will attempt to exercises to better understand what happened.

If Boeing didn't think it was important enough to mention MCAS in the QRH, why would they provide the code for it in a multi-million dollar simulator? Textron/TRU has 737 MAX Simulators in Miami as of 4/2017, but I would be shocked if they could replicate this flight. I don't think you get extra play time @ > $1,000/hour?

Ha! I think you hit the nail on the head with your first sentence. Except it should be re-written to read: "Boeing may have the ONLY simulator with MCAS functions in Seattle".

I doubt that the simulators produced by TRU and CAE have any modeling of the MCAS functionality, and even if they do, I doubly doubt there is a malfunction that allows a single AOA probe failure and corresponding cascading effects.

-GY