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Nepal Plane Crash

Old 15th Feb 2023, 20:20
  #501 (permalink)  
 
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Originally Posted by henra
This is where I'm a bit confused: Why do the engines remain feathered, when higher thrust is commanded again?
Or is it just that it takes more time than it took for the energy of the aircraft to dissipate?
Whilst not commentating on the flight condition limits (a safety function), think of sitting in a slow moving car, putting it into fifth or sixth gear then pushing the accelerator down. Not much happens... In any case it's a free turbine, propeller not directly connected to the power turbine.

Bizarre that this sort of event can happen with an experienced trainer.
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Old 15th Feb 2023, 21:07
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Thanks all for the extracts, I am also a confused non-turbo prop pilot, so bare with me.
Torque at 0 % doesn't necessairly mean exactly 0, does it? That to me imploed fuel is cut off, which doesn't seem to be the case? The engine has free turbine, has it not? Any flow over the turbine wheel would create some torque on the prop shaft, even at idle. Or is 0 a ghost number from lack of proper recording?
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Old 15th Feb 2023, 21:28
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The descent rate is going up and the houses are getting bigger. You add power, you hear the engines responding and you pull back - but there's no thrust.
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Old 15th Feb 2023, 22:14
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While I hate to point fingers and have avoided it as much as possible in previous posts, it's becoming very clear what happened. It's certainly a human error.
The other issue that stands out to me is that F30 was called for (not moved) and the condition levers placed into FTR but then F30 was stated as in position. This is unlikely to occur in the time line stated. As soon as the CLs got to feather the ACW goes off line, some residual hydraulic pressure may remain to drive the flaps to 30 but not likely. Also as soon as ACW goes off line you know about it. It's an electrical aircraft.

Originally Posted by Tu.114
Some questions to those in the know.

1. On the ATR, are the condition levers and the flap lever adjacent to each other? Yes they are next to each other but I have never seen a crew mistake the two. Both CLs have independent triggers so it would require some thought and intent to lift both at the same time

2. a. How are the condition levers and how is the flap lever protected against inadvertent movement? Latch triggers on the CLs. The Flap (which is ergonomically the shape of a flap needs to be lifted them placed into position.

b. Do the levers themselves have to be pulled out of a detent or is there a little latch mounted beneath the lever that has to be pulled to open the latch? Yes

c. Are there differences between the respective levers latch types or is the required action to unlatch the lever the same on both? As above, very very different levers and mechanisms

d. Are there differences between ATR subvariants? Yes but very minor, but a rather moot point. This crew (I believe) have only operated the 500 variant
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Old 16th Feb 2023, 01:00
  #505 (permalink)  
 
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Originally Posted by BO0M
While I hate to point fingers and have avoided it as much as possible in previous posts, it's becoming very clear what happened. It's certainly a human error.
The other issue that stands out to me is that F30 was called for (not moved) and the condition levers placed into FTR but then F30 was stated as in position. This is unlikely to occur in the time line stated. As soon as the CLs got to feather the ACW goes off line, some residual hydraulic pressure may remain to drive the flaps to 30 but not likely. Also as soon as ACW goes off line you know about it. It's an electrical aircraft.
The last sentence of paragraph 1.1.5 states that a click was recorded and a flap 'surface' movement to 30 degrees was recorded. At that time, the props were still feathered. For someone not familiar with the type (or turboprops), what power would have been available to drive the flaps to 30 degrees at that time?
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Old 16th Feb 2023, 05:20
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Old 16th Feb 2023, 06:12
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Flap 15 and Condition Auto would be lining up . The Width of the top knobs seems similar . Can something like this be messed up especially by the PM .

Last edited by Yo_You_Not_You_you; 16th Feb 2023 at 08:12.
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Old 16th Feb 2023, 07:26
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An image for those who don't want to suffer the music in the Youtube video above.

Originally Posted by 4forward8back
The last sentence of paragraph 1.1.5 states that a click was recorded and a flap 'surface' movement to 30 degrees was recorded. At that time, the props were still feathered. For someone not familiar with the type (or turboprops), what power would have been available to drive the flaps to 30 degrees at that time?
Where do the generators and pumps attach to the engine? If they're driven by the engine core, the feathered props are not a factor, the engines would still drive the accessories and therefore hydraulic power and electrical power remains available. I don't know these engines though, so I could be wrong here.
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Old 16th Feb 2023, 07:29
  #509 (permalink)  
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While the uncommanded auto-feather looks one of the probable causes, I have read somewhere that there should be a mecahnism that prevent to do this on both engines at the same time . So that safety would have failed too ?
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Old 16th Feb 2023, 08:54
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@Boom, thank You for the answers. Together with the picture of the quadrant, it does seem to point into a certain direction.

1. The propellers feathered at the same time the flaps were supposed to go to 30. It stretches my imagination a bit to assume an unscheduled feather to strike both engines right at this time, without autofeather armed and bypassing all the internal safety nets such as the mentioned lockout on the far engine.

2. Looking at the quadrant, not only are the flap lever and the condition levers right beside each other. Also, their respective position may well have been quite similar. I obviously stand to be corrected here, but I gathered that the condition levers are normally in "AUTO" in this flight phase - the flap lever was in position 15°, so they were rather adjacent to each other. Additionally, the required travel from 15° to 30° on the flap levers seems rather similar to the travel from AUTO to FTR on the condition levers. The haptic differences between two versus one lever and the very different unlatching actions seem to be the only remaining 2 cheese layers that prevent a misselection in a rather high-workload situation in which the often-performed selection may be performed without looking at what lever is being grabbed.

About the engines and their connection to the hydraulic pumps, as the question was asked: On a PW120, the hydraulic pump is mounted on the propeller reduction gear box along with the variable frequency AC generator and other things. The turbomachinery drives the DC starter generator that generally speaking provides the low(er) watt systems. If one propeller is feathered and the other is running, the good engine will provide power to the failed engines hydraulic system in some way (be it via an AC electric auxiliary pump or a unidirectional PTU), but with all engines feathered, hydraulics will generally end up unpressurised, whether or not the turbomachinery is still running.

Last edited by Tu.114; 16th Feb 2023 at 11:37.
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Old 16th Feb 2023, 09:00
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Auto-feather can feather only one side.
This was commanded feathering so no protection against feathering both sides.

The ACW and hydraulic loss was mentioned and explained in post #500.In addition the flight spoilers are lost as well.

On the old 72 with 4 blade propeller and without PEC the „Automatic Propeller Changeover to MAX RPM“ might have saved the day.
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Old 16th Feb 2023, 09:57
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Originally Posted by Tu.114

About the engines and their connection to the hydraulic pumps, as the question was asked: On a PW120, the hydraulic pump is mounted on the propeller reduction gear box along with the variable frequency AC generator and other things. The turbomachinery drives the DC starter generator that generally speaking provides the low(er) watt systems. If one propeller is feathered and the other is running, the good engine will provide power to the failed engines hydraulic system in some way (be it via an AC electric auxiliary pump or a unidirectional PTU), but with all engines feathered, hydraulics will generally end up unpressurised, whether or not the turbomachinery is still running.
You are mixing up Dash8-400 (PW150) and ATR 72 (PW124&127) again.
On theATR there is no hydraulic coming from the engine.
The hydraulic pumps are electrical driven and located in the belly.If one engine is running with Np above 66% both ACW buses are supplied and both hydraulic pumps are running.
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Old 16th Feb 2023, 11:37
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Thank You for the correction, I´ll amend my previous post shortly.

Still, it means that with both propellers feathered, there is no hydraulic power on the ATR, correct?

By the way, are any of the primary flight controls hydraulically powered on the ATR? With a total hydraulic loss, are there any implications to the aircraft controlability?
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Old 16th Feb 2023, 11:46
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The frequency-wild generators
drop off line when the propeller rpm falls below 70%. In
operational terms, this means that when the propellers’
rpm are reduced prior to feathering following the
aircraft’s arrival on stand, the Green and Blue system
AC pumps will cease operating. This will cause the
DC pump, powered from starter/generators on the
high-speed engine spools, to cut in, thus maintaining
pressure in the Blue system.
From: http://www.aaiu.ie/sites/default/fil...2009-10-21.pdf. Not sure if it is the exact same model of ATR-72, but pretty close I guess.
Also:
Each hydraulic system is provided with a 0.2 litre
accumulator, which damps out pressure surges and
compensates for pump response time in the event of
high demand.
Between the accumulator(s) and the possibility that the DC pump was supplying pressure to the Blue system, which feeds the flap actuation system, the flaps extending from 15 to 30 degrees appears to be possible with both props feathered based on the description in the report linked to above.
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Old 16th Feb 2023, 13:51
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Think i was wrong.I missed the signal „LDG Lever down“ in the wiring manual.Sorry.

The DC AUX Pump should take over when blue hyd press is low,at least one engine running(signal is oil press) and the LDG is selected down.
Operation of flaps should be possible now.
Movement will be slower due to much smaller pump.
Flight spoilers should work as well.
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Old 16th Feb 2023, 15:56
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As one contributor commented at the time, and on listening to the first video posted, there is, now we know more, remarkably little prop noise. A few questions

Is there any kind of protection on the ATR to prevent what is quite a simply made error - even an audible cancellable warning.

This was commanded feathering so no protection against feathering both sides
- sorry just found this - but isn't this a case of if it can happen it will so should there be. Even on a little RV-7 I fly in there is a "flaps flaps" audible warning when they move

Had the error been detected quickly would this have been recoverable. Presume so.

Tragic out come from moving the wrong lever.
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Old 16th Feb 2023, 17:12
  #517 (permalink)  
 
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Originally Posted by Tu.114
2. Looking at the quadrant, not only are the flap lever and the condition levers right beside each other. Also, their respective position may well have been quite similar. I obviously stand to be corrected here, but I gathered that the condition levers are normally in "AUTO" in this flight phase - the flap lever was in position 15°, so they were rather adjacent to each other. Additionally, the required travel from 15° to 30° on the flap levers seems rather similar to the travel from AUTO to FTR on the condition levers.
Indeed the position is quite close to each other.
Buuuut:
The haptic differences between two versus one lever and the very different unlatching actions seem to be the only remaining 2 cheese layers that prevent a misselection in a rather high-workload situation in which the often-performed selection may be performed without looking at what lever is being grabbed.
The shape of the levers and the unlatching mechanism are indeed veeeery different. That is probably why this hasn't happened before (at least not with such consequences that I'm aware of).
The chances that in this case indeed a mix- up did happen appear to be high. Remains pretty puzzling, though. Also that apparently no one checked position of the levers even when after applying power nothing happened. Normally even peripheral vision should have been enough to ring a bell. And all this in bright daylight. And no cacophony of alerts, No direct emergency that would have caused havoc in the cockpit. Nothing which would explain why it a) happened in the first place and b) wasn't detected afterwards. But from the basic facts we know chances are still very high that exactly this happened.
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Old 16th Feb 2023, 19:06
  #518 (permalink)  
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The shape of the levers and the unlatching mechanism are indeed veeeery different.
Indeed and it is why Ihave a bit difficulties in accepting a simple lever mix up. In addition to what you said, the flaps is one lever, conditions are 2 , and as someone explained earlier there should be specific buttons to push of pull to go to feather. These facts combined with quite experienced pillots , which had done 3 evious flights on the same aircraft that day , almost CAVOK., no real stress or emergency , just a request for a QFU change , it does not really add up.. .I think we are missing something here.
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Old 16th Feb 2023, 19:38
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Originally Posted by henra
Indeed the position is quite close to each other.
... Also that apparently no one checked position of the levers even when after applying power nothing happened. Normally even peripheral vision should have been enough to ring a bell. And all this in bright daylight. ... But from the basic facts we know chances are still very high that exactly this happened.
Even more puzzling:
10:56:32: The PF then called for “FLAPS 30” at 10:56:32, and the PM replied, “Flaps 30 and descending”. The ...(FDR) data did not record any flap surface movement at that time. Instead, the propeller rotation speed (Np) of both engines decreased simultaneously to less than 25%1 and the torque (Tq) started decreasing to 0%, which is consistent with both propellers going into the feathered condition2. ..
10:56:54, another click was heard, followed by the flaps surface movement to the 30 degrees position...

That sounds to me like someone noticed the mistake after 20 s and pulled the flap levers to 30. Clandestine correction of error with no comment on the CVR and no check / correction of the condition levers?
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Old 16th Feb 2023, 19:52
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If an error can be made, however unlikely, humans will find a way of making it. They will even hear, see and confirm what they expect to happen. Neither pilot seemed to notice a sudden and complete loss of power. Well, why would they, it wasn't in the mental model.
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