ET crash ADD NBO

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Fox3WheresMyBanana
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Re: ET crash ADD NBO

#301 Post by Fox3WheresMyBanana » Sun Mar 24, 2019 2:47 pm

From similar situations on the F3 sim, if the flight controls lecturer was also a sim instructor (as I was), then the failure of the MCAS could be worked out, and simulated by, say, the AoA gauge* being failed to full deflection (if this is even possible, maybe failing the AoA Disagree* instead), and the instructor manually blipping the stabilizer trim in the manner that a failed MCAS would. Given the way the MCAS works, this would need a sim instructor watching the use of the trim button, which cuts out MCAS for a time, and using a stopwatch. Again, the caveat is that the sim instructor would have needed a brief to make the sim realistic, and not just run through the stock minimum of standard drills. With the Lion Air report not yet published however, it is unlikely that any sim instructor would have added 'AoA sensor to MCAS' to his/her 'repertoire of interesting failures'. One only wants to give things which are known to occur.



*not that this would have helped the Ethiopian lot, since they had neither fitted.

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Re: ET crash ADD NBO

#302 Post by Mrs Ex-Ascot » Sun Mar 24, 2019 3:25 pm

Fox3 and Boac thank you both for your interesting replies. I guess there is only so much you can cover in simulator training. So it basically boils down to having at least one experienced and well trained pilot on board, even if he/she is in the jump seat hitching a ride. :)
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Re: ET crash ADD NBO

#303 Post by Boac » Sun Mar 24, 2019 4:02 pm

Well, in theory ALL pilots (crew) are 'well trained' having been through a training course and been tested. What scuppers the plan big time is having a system on board of which the crew know nothing and which behaves in a way they are not used to. I found in my time on the 73 that STS was an unnecessary (to me) function which I found confusing, but I learnt to live with it. Had someone chucked in a trim that repeatedly but not continuously (refer checklist) operated to trim me nose-down I would have been again 'confused'. For how long I know not. I would hope that when I realised that the a/c was fighting me the whole time with trim I would have disconnected the trim (even not knowing what was happening and with the event not really fitting with the drill) but I was not there with a brand-spanking new F/O. I like to think I would not have let the a/c accelerate as it did, worsening the control problem. Why they did is still a big mystery in both accidents for me. I fear that the conscious or sub-conscious thought would have been that IF they throttled back there would be another nose-down trim change, which they were already fighting.

I would very much like to know what the enquiry into Boeing's conduct here finds regarding the fault analysis of this system and whether any pilots or engineers had reservations which were suppressed.

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Re: ET crash ADD NBO

#304 Post by boing » Sun Mar 24, 2019 5:08 pm

If you think about this event there are logical deductions that can be made.

1. If this was a software problem then many more events should have taken place by this time. It is more than likely that all buyers receive the same software code in their MCAS installations.
2. An AOA vane is driven by airflow, it cannot motor itself to an incorrect position. This leaves three possibilities.
a. The erroneous AOA information appeared in flight. This would imply a fault in the AOA electronics signal rather than the vane itself since the vane could not assume a grossly incorrect position against the airflow. However, this leads to the question why have we not seen more events?
b. The AOA vane was jammed into the wrong position prior to take off, was not blown to the correct position by 200 kts of airflow and its incorrect position was only significant when the flaps were retracted. This is a little unlikely unless the vane had been badly damaged in a ground incident.
c. In both accidents the AOA vane received a birdstrike. Highly unlikely but possible.
3. Since the AOA system was continuously providing incorrect information the MCAS system would have continuously attempted to trim the stabiliser nose down whenever the electronic trim buttons were not in use. This would be a very difficult problem for the pilots to troubleshoot in the time available. It is not clear to me whether operation of the trim buttons would actually reverse the movement of the stab. or simply prevent it motoring any further nose down.
4. The standby manual trim wheels on the Boeing 7XX are too slow to counteract the stab. drive system trim switch command although I seem to remember that moving the manual trim wheel in the opposite direction to that selected by the trim buttons on the 727 would deliberately jam the trim system preventing further movement.
5. The stab. trim cut-outs should have worked but this would depend upon exactly how they are wired into the system. Conceivably some genius could have decided that since a high AOA situation is a danger to safety the stab. trim system could be wired to ignore the cutout. Unlikely but we are dealing with engineers here.

Presently I am favouring corrupt AOA signals due to a connector problem or Printed Circuit Board preparation error on a batch of AOA sensors. This led almost inevitably to the accidents since the persistent nose down stab. movement eventually overpowered the elevator controls and drove the aircraft into the ground.

Interestingly there was an RAF pilot who got a gong, an AFC I think, and an ETPS slot for controlling his Canberra, which had a nose-down runaway trim fault at 250 feet low-level, until his navigator baled out and he ejected. This involved making a series of climbing, negative G, barrel rolls until he gained some height - not really a trick for an airliner.


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Re: ET crash ADD NBO

#305 Post by Boac » Sun Mar 24, 2019 5:56 pm

Concur with all of that, Boing. I think 3) a persistent nose-up pickle should motor at the flaps up rate, but not sure.

Again, however, the question - why only these 3 or do we just not have the reports?

LATEST:
The Wall Street Journal reports that the Federal Aviation Administration has “tentatively approved sweeping software and pilot-training changes” for Boeing’s 737 MAX jet, a fix that could allow pilots to exert more control over an automated system that is thought to have been the cause of a deadly crash in Ethiopia last week, and could allow carriers to being flying the grounded aircraft once again.

The WSJ says that the software updates will scale back the Maneuvering Characteristics Augmentation System (MCAS) redesigning it “so it won’t overpower other cockpit commands or misfire based on faulty readings from a single sensor,” and will only activate once, for a short duration in the event that there is an issue. The FAA has “tentatively approved,” the update, but it needs to go through simulations and flight testing.

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Re: ET crash ADD NBO

#306 Post by Undried Plum » Sun Mar 24, 2019 7:32 pm

Does that mean that the stick force per g at high alpha will still be outside (ie below) the limits of normal airworthiness certification for a civil airliner?

At what point does the FAA say "enough already! This thing is not the same airplane as the 737-100. It needs a new type certificate"?

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Re: ET crash ADD NBO

#307 Post by Fox3WheresMyBanana » Sun Mar 24, 2019 7:44 pm

Anyone's guess, considering that it should not have been, and still shouldn't be, certified.

The Europeans and Canadians are currently investigating, especially as current certifications by them are done 'on trust' from the FAA.

https://globalnews.ca/news/5072383/cana ... g-737-max/

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Re: ET crash ADD NBO

#308 Post by k3k3 » Sun Mar 24, 2019 9:37 pm

When NATO was getting its brand new E-3As some of them, two or three in a row IIRC, had a constant discrepancy between the AOA indications, eventually it was determined that the person drilling the mounting and keyway holes for the AOA probes at the factory had not turned the template over when moving from the left to the right side of the nose.

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Re: ET crash ADD NBO

#309 Post by Boac » Sun Mar 24, 2019 9:45 pm

Amazing! It may merit checking the construction records to see who drilled the holes on the 2 aircraft - and if he/she did others.

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Re: ET crash ADD NBO

#310 Post by k3k3 » Sun Mar 24, 2019 9:53 pm

By the time the, disbelieving at first, Boeing engineers arrived at Geilenkirchen they and we had figured out what had gone wrong, the engineer walked up to the aeroplane, played with his glasses, and said "I see what's wrong".

Boeing make some amazing spectacles, they may have forgotten how to by now as it was 35 years ago.

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Re: ET crash ADD NBO

#311 Post by Slasher » Mon Mar 25, 2019 1:44 am

Doing the rounds here among HKG sim destructors...

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Re: ET crash ADD NBO

#312 Post by Boac » Mon Mar 25, 2019 8:01 am

'Minor' bug fixes??

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Re: ET crash ADD NBO

#313 Post by izod tester » Mon Mar 25, 2019 8:42 am

It only says minor bug fixes - It doesn't claim to have fixed all the bugs.

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Re: ET crash ADD NBO

#314 Post by Boac » Mon Mar 25, 2019 8:50 am

Boeing holding 'big briefing' for MAX customers in Renton on Wednesday. ET probably not going....................

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Re: ET crash ADD NBO

#315 Post by barkingmad » Mon Mar 25, 2019 9:26 am

Well of course it's a "minor bug fix" if it is applicable to or installable by "Age 4+" ! ! !

Good spoof guys!

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Re: ET crash ADD NBO

#316 Post by llondel » Tue Mar 26, 2019 2:35 am

The problem is that the bug that needs fixing isn't minor.

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Re: ET crash ADD NBO

#317 Post by Boac » Tue Mar 26, 2019 8:08 am

On Saturday, Southwest Airlines began to send some Boeing 737 MAX 8 fleet to its long-term storage facility.

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Re: ET crash ADD NBO

#318 Post by ian16th » Tue Mar 26, 2019 10:54 am

Cynicism improves with age

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Re: ET crash ADD NBO

#319 Post by Fox3WheresMyBanana » Tue Mar 26, 2019 10:37 pm

As a whole, it isn't. If it was, then certification of the MCAS wouldn't have been moved to Boeing.
Certain senior managers at the FAA are though. The ones who suggested then authorised the MCAS transfer.

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Re: ET crash ADD NBO

#320 Post by llondel » Wed Mar 27, 2019 3:05 am

Boac wrote:
Tue Mar 26, 2019 8:08 am
On Saturday, Southwest Airlines began to send some Boeing 737 MAX 8 fleet to its long-term storage facility.
About that...

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