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Indonesian aircraft missing off Jakarta

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Indonesian aircraft missing off Jakarta

Old 23rd Nov 2018, 12:36
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Originally Posted by xetroV
I wonder when AOA DISAGREE would have shown during this flight. Judging from the FDR data, the AOA bias already existed at lift-off, so could it have been during the takeoff roll, prior to V1?
It was previously written in this thread that the AOA DISAGREE alert only exists when the PFDs are fitted with an AOA display.

Anyway Air Data disagree errors are most likely coupled to being in the air and don't show on the takeoff run.
Or can UAS be displayed during the takeoff run? I don't know.
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Old 23rd Nov 2018, 12:43
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Originally Posted by wiedehopf
It was previously written in this thread that the AOA DISAGREE alert only exists when the PFDs are fitted with an AOA display.
I've read large parts of the thread, but not all of it. In our NG fleet we do have an AOA DISAGREE alert, but no AOA display (except implicitly via the flight path vector).

And since a faulty AOA can mess up flight data such that an experienced crew can get overwhelmed to the extent of crashing their aircraft, I wonder why Boeing offers the AOA DISAGREE alert as a customer option in the first place. That makes as much sense to me as offering optional engine fire warning loops...

Last edited by xetroV; 23rd Nov 2018 at 12:53. Reason: Added afterthought
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Old 23rd Nov 2018, 13:19
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Originally Posted by lomapaseo
That's like adding floor lamps in your room to offset any bulbs that may burn out. In the end you would be tripping over all the wires wondering which lamp they go. I shudder to think about the same mess of wires in a plane
Pretty sure that something like "mess of wires" was what I thought on seeing an aircraft wiring loom (in construction) for the first time Up close of course it isn't a mess, it's all neat and labelled etc., but first sight it's like a giant spaghetti monster had a multicoloured yawn, with lumps in.

But if we're doing multiple secondary flight recorders, why not go wireless? Makes retrofit feasible too - one wireless transmitter at the existing DAU, possibly some relay transmitters, and multiple receiver-CSMU units. Storage capacity and size won't be a problem - we're heading towards a terabyte on a single micro SD - crash survivability will need some work but it should be much easier to make small things survivable.

The really big question isn't can we do it, it is why? With the existing system the number of accidents where we find the aircraft but don't find the recorders really is minimal, the benefit side of the equation just isn't going to justify the costs. I do have to admit to thinking more than once that the airbus composite fins would be an excellent place for a secondary CSMU - they do seem to have a detaching, surviving and floating capability already built in.
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Old 23rd Nov 2018, 13:28
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Originally Posted by AGBagb
I wonder if he actually said that, or meant it if he did?
I wonder if there was a word or two lost in translation and what was meant was "after it thought it stalled". Yes, we all know the aircraft doesn't think as such, but "the aircraft thought it was stalling and therefore nose dived" is as good as you are going to get for a one-line description of this accident.
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Old 23rd Nov 2018, 13:41
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This quote from Avherald on KNKT presentation to Parliament:
" On the previous flight from Denpasar to Jakarta the same problem existed, the automatic trim inputs however did not occur. The crew must have done something preventing the MCAS system producing the nose down trim inputs."
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Old 23rd Nov 2018, 13:50
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Originally Posted by FiveGirlKit
  • 2 AoA probes have the same fault - the one replaced and the one fitted (unlikely, but not impossible)
Actually as far as i know the AoA probe replacement was carried out not before the accident flight but prior to the previous flight.

I have not yet seen FDR data from the flights that triggered the replacement i would assume they are uninteresting with no or minor AoA disagree otherwise they would have been in the slides)

So no there were no 2 probes with the same fault, there was just no replacement or check done on the AoA sensor after the stick shaker went off or an entire sector.

b1lanc wrote:
This quote from Avherald on KNKT presentation to Parliament:
" On the previous flight from Denpasar to Jakarta the same problem existed, the automatic trim inputs however did not occur. The crew must have done something preventing the MCAS system producing the nose down trim inputs."
To me the FDR data looks like the crew disabled electric trim with the cutout switches.
This is actually quite clear because the trace for manual electric trim and automatic electric trim show nothing while the Trim Position changes.

Actually at the start of that flight the exact same problem occured and you can see the same "fight" between the pilots using electric trim vs the MCAS system.
I'm sure it's just a unlucky choice of words over at the avherald and will most likely soon be corrected.
He probably meant that the automatic trim inputs no longer occured after the crew used the CUTOUT switches or disabled the computer system producing the MCAS trim inputs.
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Old 23rd Nov 2018, 14:35
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Yes, on that previous flight, you can see the fight between manual electric and automatic trim inputs. In one 50-second stretch, the aircraft goes from 4400 to 5600 feet, back down to 4400, and up to 5600. Someone want to imagine what that would feel like?
It looks like they used the manual electric trim to fight the MCAS for another 45-50 seconds, and then hit the cut-out. You can see the MCAS makes one last nose-down command that doesn't translate into trim movement. 150 seconds later, as they're considerably higher, they try again, disabling the cutout and immediately ordering nose-up trim. MCAS gave them a whole bunch of nose-down, so they cutout again and manually cranked the desired trim.
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Old 23rd Nov 2018, 15:02
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Originally Posted by wiedehopf
Actually as far as i know the AoA probe replacement was carried out not before the accident flight but prior to the previous flight.
Yes, that is my understanding as well, and it's not a trivial point. The page of the aircraft maintenance log for the flight prior to the accident flight has been published online. There is no mention of an AoA sensor being replaced.
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Old 23rd Nov 2018, 15:04
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Originally Posted by infrequentflyer789
I do have to admit to thinking more than once that the airbus composite fins would be an excellent place for a secondary CSMU - they do seem to have a detaching, surviving and floating capability already built in.
Which sometimes activates in anticipation of the accident.
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Old 23rd Nov 2018, 15:58
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Originally Posted by A Squared
Yes, that is my understanding as well, and it's not a trivial point. The page of the aircraft maintenance log for the flight prior to the accident flight has been published online. There is no mention of an AoA sensor being replaced.
IIRC, the NTSC stated that there had been four previous (not necessarily consecutive) flights during which similar problems had been encountered, and that at some stage during that sequence the AoA sensor had been replaced.
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Old 23rd Nov 2018, 15:59
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DingerX, this image illustrates what you're stating - STS/MCAS trims ND, manual input NU, etc.:

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Old 23rd Nov 2018, 16:46
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Or, for the previous flight, the red lines mark where the cutout comes in. In both cases, the last automatic call for ND trim occurs without corresponding trim movement. The second time, they try to give it a bit of NU trim, only to be countermanded. Cutout again, and the trim moves NU without electrics.
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Old 23rd Nov 2018, 18:01
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Root cause . AOA sensor issue . So what is that ? . Wiring issue ; probe issue ; probe mounting issue ; sensor issue , analyser issue / damage ; rogue components ; position of analyser mounting . Alignment fixing issue , mount damage ; and the list goes on
What constitutes a replacement ? . A complete assembly or part of ? .
Whatever - the problem was not solved ; put a trouble shooter on board - to do what ? . Maintenance from previous flight targeted problem , trouble shoot by " the book " still a concern . Then we have the flight managment control issues , just as an addition . .. ohh hell .
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Old 23rd Nov 2018, 18:03
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Originally Posted by DaveReidUK
IIRC, the NTSC stated that there had been four previous (not necessarily consecutive) flights during which similar problems had been encountered, and that at some stage during that sequence the AoA sensor had been replaced.
4 flights with UAS (and I guess I inferred consecutive) is what I remember - don't recall any mention of AoA disagree for the first two or at least it wasn't mentioned. Notably the FDR readouts weren't supplied (logs weren't leaked either) subsequent to those earlier flights. AoA sensor was replaced between segments 2 and 3.

From Aviationtoday.com:
" On Nov. 5, CNN published an update on the crash investigation from Capt. Nurcahyo Utomo of Indonesia's National Transportation Safety Committee (KNKT) noting that the FDR review also concluded that the aircraft airspeed indicator was malfunctioning on four consecutive flights prior to the crash. Utomo also indicated the pilots should have recognized the malfunction when it occurred on flight JT610."
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Old 23rd Nov 2018, 18:04
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Don't know anything about the relevant actuator, but unless the actuator has a brake or an effective (electrical) detent, very interesting things can happen with vibration.
Which therefore suggests that the relevant actuator must have an effective brake/detent, given that any screw can be revers driven in appropriate circumstances.
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Old 23rd Nov 2018, 18:10
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The most extensive over-ride capability is provided by the Embraer EMB-145, where a single push button on the yoke disables or disengages the stick pusher, the auto-pilot, and the elevator trim system. The Canadair CRJ has a toggle switch next to the captains knee that can be used to deselect the stick pusher. Since the pilot has the ultimate responsibility for the safe conduct of the flight, the ability to over-ride a malfunctioning system is of utmost importance
ALPA

The answer is to give the pilot(s) a quick means of disabling all alarms so that they can restore calm
in the cockpit and fly the plane.If an anti-stall device is actually going to independently operate flight controls (primary or auxiliary),as in the case of this MCAS,then they have to go back to the drawing board and look again at how to prevent false ADIRU data triggering these devices(no easy task obviously).It is one thing to get a false stick shaker.It is entirely another thing to get the FCC commanding operation of flight controls based on false data.
Over and out.
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Old 23rd Nov 2018, 18:16
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Originally Posted by DType
Vibration can enable a normally irreversible screw to reverse.
Originally Posted by Concours77
Absent command, the jackscrew cannot rotate....
Maybe it can, maybe it can't (my money would be on not).

But either way - what is the relevance?

Given the overwhelming evidence implicating the STS/MCAS, why are we throwing Occam's Razor out of the window and postulating an unrelated, independent mechnical failure of the actuation mechanism as a causal factor?

The MAX has the same horizontal stabilizer as the NG, and I'd bet that the actuator/gearbox/jackscrew isn't significantly different either. How many NG loss of pitch trim control incidents have there been in the last 20 years that have been attributable to actuation failure?
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Old 23rd Nov 2018, 18:33
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Excellent point. See you in Tech Log?
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Old 23rd Nov 2018, 18:50
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Originally Posted by b1lanc
4 flights with UAS (and I guess I inferred consecutive) is what I remember - don't recall any mention of AoA disagree for the first two or at least it wasn't mentioned. Notably the FDR readouts weren't supplied (logs weren't leaked either) subsequent to those earlier flights. AoA sensor was replaced between segments 2 and 3.
Your inference is indeed correct. This report of the Nov 5th press briefing quotes the three preceding UAS events as occurring on:

Denpasar-Manado
Manado-Denpasar
Denpasar-Jakarta

which were of course consecutive.

Elsewhere it was confirmed that the AoA sensor was changed at Denpasar on October 28th.
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Old 23rd Nov 2018, 19:02
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ballscrew-backscrew backdriven

RE JACKSCREW- EG BALLSCREW - being backdriven -- PLEASE SEE MY POST 1522 this thread
Quote:
Originally Posted by DaveReidUK Correct me if I'm wrong, but the coarser the thread pitch (all other things being equal), the more likely a jackscrew is to be back driveable (the spiral ratchet screwdriver principle). Is that what you're saying?

I can't see air loads on the stab being capable of overcoming the combined braking friction in the jackscrew, gearbox and actuator unless we're talking about a previously undisclosed failure in addition to the issues already discussed.
Its MORE than just the pitch ( lead) please take the time to read this simplified explanation

https://www.linearmotiontips.com/how...ll-back-drive/

and for an approximation of loads

https://www.aerospaceonline.com/doc/...actuators-0001

+++++++


Originally Posted by DaveReidUK
Maybe it can, maybe it can't (my money would be on not).

But either way - what is the relevance?

Given the overwhelming evidence implicating the STS/MCAS, why are we throwing Occam's Razor out of the window and postulating an unrelated, independent mechnical failure of the actuation mechanism as a causal factor?

The MAX has the same horizontal stabilizer as the NG, and I'd bet that the actuator/gearbox/jackscrew isn't significantly different either. How many NG loss of pitch trim control incidents have there been in the last 20 years that have been attributable to actuation failure?
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