Nepal Plane Crash
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Might have been in the early pistons aircraft types when it was introduced, but all the events I remember were I always at or right after take off , Having that on base leg with reduced power ? and as you said, on both engines at the same time ? Weird.
Drain Bamaged
Disclaimer: I'm in no point saying that's what happened there but that is a possible scenario on another type of aircraft.
A possibility is that they may have been too high to change runway and decided to put the engines into 100% over-ride (fine pitch) using the condition levers to create drag and maybe move them back to the Auto position when they got on the new profile but mistakenly brought them to feather.
A few words on autofeather systems, again from a DH8 perspective (that comes with the same PW120 series engines the ATR uses as well).
Generally, they are only armed for takeoff, as this is when an unfeathered propeller will have the most performance impact (and yes, an engine failure during go around will consequently by default require manual feathering). Arming conditions are (roughly) the following:
- Selection by flight crew
- Both power levers above a certain angle
- Both torques above a certain threshold.
That fulfilled, the system will feather a propeller in case of one engines torque dropping below a defined threshold for a defined time; on the Dash 8-400 it was 25% for 3 seconds IIRC (it has been a while). This will trigger:
- a feather command to the affected propeller control unit, also involving the alternate feather pump,
- most importantly, a cutout signal to the other, good engine to inhibit autofeathering on that side.
So even if autofeather should fire by error on one engine, it would take additional system malfunctions for it to affect both engines at once. Even in the previously quoted case of the Taiwanese ATR, I understand that the malfunction affected only one of the engines and the systemic safety barriers worked, keeping the fault manageable in principle.
If indeed both propellers ended up feathered on the accident flight, this would most likely not be due to autofeather imho. Rather, some flight crew action would have to have been involved to achieve this. The other ways of feathering a propeller would be pushing the associated alternate feather push button (activating an oil pump drawing engine oil from a dedicated reservoir to force the prop into feather) or pulling the condition lever back to low RPM, lifting it out of the reached detent and further pulling it to start/feather position. But none of this seems appropriate in final approach; as has been mentioned, the condition levers are either (type and situation dependent) left in low RPM or pushed forward into max RPM position.
Generally, they are only armed for takeoff, as this is when an unfeathered propeller will have the most performance impact (and yes, an engine failure during go around will consequently by default require manual feathering). Arming conditions are (roughly) the following:
- Selection by flight crew
- Both power levers above a certain angle
- Both torques above a certain threshold.
That fulfilled, the system will feather a propeller in case of one engines torque dropping below a defined threshold for a defined time; on the Dash 8-400 it was 25% for 3 seconds IIRC (it has been a while). This will trigger:
- a feather command to the affected propeller control unit, also involving the alternate feather pump,
- most importantly, a cutout signal to the other, good engine to inhibit autofeathering on that side.
So even if autofeather should fire by error on one engine, it would take additional system malfunctions for it to affect both engines at once. Even in the previously quoted case of the Taiwanese ATR, I understand that the malfunction affected only one of the engines and the systemic safety barriers worked, keeping the fault manageable in principle.
If indeed both propellers ended up feathered on the accident flight, this would most likely not be due to autofeather imho. Rather, some flight crew action would have to have been involved to achieve this. The other ways of feathering a propeller would be pushing the associated alternate feather push button (activating an oil pump drawing engine oil from a dedicated reservoir to force the prop into feather) or pulling the condition lever back to low RPM, lifting it out of the reached detent and further pulling it to start/feather position. But none of this seems appropriate in final approach; as has been mentioned, the condition levers are either (type and situation dependent) left in low RPM or pushed forward into max RPM position.
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The Nepal crash also happened in a low-level/low-speed regime, so very little room to make mistakes, once "something auto" goes haywire. When a full power on the remaining engine is not immediately applied, the 20-30% reserve above the stall speed is energy wise lost pretty fast (a couple of seconds). Sinking starts and the natural tendency to pull-up completes the crash preparation into unavoidable.
Did this happen: I don't know, though it is certainly a plausible mechanism, this kind of accidents develop very fast from "normal" to "irrecoverably", especially, when "the other engine" is also feathered due to confusion.
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A few words on autofeather systems, again from a DH8 perspective (that comes with the same PW120 series engines the ATR uses as well).
Generally, they are only armed for takeoff, as this is when an unfeathered propeller will have the most performance impact (and yes, an engine failure during go around will consequently by default require manual feathering). Arming conditions are (roughly) the following:
- Selection by flight crew
- Both power levers above a certain angle
- Both torques above a certain threshold.
That fulfilled, the system will feather a propeller in case of one engines torque dropping below a defined threshold for a defined time; on the Dash 8-400 it was 25% for 3 seconds IIRC (it has been a while). This will trigger:
- a feather command to the affected propeller control unit, also involving the alternate feather pump,
- most importantly, a cutout signal to the other, good engine to inhibit autofeathering on that side.
So even if autofeather should fire by error on one engine, it would take additional system malfunctions for it to affect both engines at once. Even in the previously quoted case of the Taiwanese ATR, I understand that the malfunction affected only one of the engines and the systemic safety barriers worked, keeping the fault manageable in principle.
If indeed both propellers ended up feathered on the accident flight, this would most likely not be due to autofeather imho. Rather, some flight crew action would have to have been involved to achieve this. The other ways of feathering a propeller would be pushing the associated alternate feather push button (activating an oil pump drawing engine oil from a dedicated reservoir to force the prop into feather) or pulling the condition lever back to low RPM, lifting it out of the reached detent and further pulling it to start/feather position. But none of this seems appropriate in final approach; as has been mentioned, the condition levers are either (type and situation dependent) left in low RPM or pushed forward into max RPM position.
Generally, they are only armed for takeoff, as this is when an unfeathered propeller will have the most performance impact (and yes, an engine failure during go around will consequently by default require manual feathering). Arming conditions are (roughly) the following:
- Selection by flight crew
- Both power levers above a certain angle
- Both torques above a certain threshold.
That fulfilled, the system will feather a propeller in case of one engines torque dropping below a defined threshold for a defined time; on the Dash 8-400 it was 25% for 3 seconds IIRC (it has been a while). This will trigger:
- a feather command to the affected propeller control unit, also involving the alternate feather pump,
- most importantly, a cutout signal to the other, good engine to inhibit autofeathering on that side.
So even if autofeather should fire by error on one engine, it would take additional system malfunctions for it to affect both engines at once. Even in the previously quoted case of the Taiwanese ATR, I understand that the malfunction affected only one of the engines and the systemic safety barriers worked, keeping the fault manageable in principle.
If indeed both propellers ended up feathered on the accident flight, this would most likely not be due to autofeather imho. Rather, some flight crew action would have to have been involved to achieve this. The other ways of feathering a propeller would be pushing the associated alternate feather push button (activating an oil pump drawing engine oil from a dedicated reservoir to force the prop into feather) or pulling the condition lever back to low RPM, lifting it out of the reached detent and further pulling it to start/feather position. But none of this seems appropriate in final approach; as has been mentioned, the condition levers are either (type and situation dependent) left in low RPM or pushed forward into max RPM position.
What is SOP on the ATR?
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Yes plus the rather long post accident fire kind of contradict this. Plus in fuel stavation accidents ,including the previously mentioned Tunisair ATR, engines normally do not stop at the same time .
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Excuse my ignorance, never flown a turboprop. On flame out is the ATR designed to autofeather automatically without crew input? What are the implications when it comes to restart? If they've gone into full feather you'd need a starter assisted restart?
I am trying to relate to the recent Dash 8 in Norway who had several flame outs on approach as ice shed into the air intakes. The engines were out for about 25-35 seconds each but the auto-ignition turned the fire back on. How would that have worked if they'd gone into feather upon loss of torque?
I am trying to relate to the recent Dash 8 in Norway who had several flame outs on approach as ice shed into the air intakes. The engines were out for about 25-35 seconds each but the auto-ignition turned the fire back on. How would that have worked if they'd gone into feather upon loss of torque?
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For the Autofeather to happen certain conditions have to be met. Those conditions are there during the T/O, and during the APP, after an action that happens after putting the Gear Down. Other than that, the Autofeather will not happen automatically.
If they've gone into full feather you'd need a starter assisted restart?
It is worth noting that the feathering of the propeller does not shut down the engine. The engine can still be running with the propeller feathered.
About the Dash 8, don't know anything about it, but my understanding is that it has more power than the ATR.
It has been established that both engine propellers went into feather. We will have to wait to learn if that was caused by system malfunction, or if it was crew error when intending to reach for the Power Levers, or even for the Flap Lever, they instead reached for the Condition Levers.
Last edited by zerograv; 10th Feb 2023 at 19:21. Reason: typo and add information
172, props that are feathered do not need a starter to un-feather,depending where the `condition lever/button is,.The act of unfeathering should start the engine as well..
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@ Zerograv :
Not familiar with the ATR quadrant, but looking at a photo, do you mean that : 1) retarding the conditions levers to Fuel shut off would automatically feather the props and 2) there is no push or pull button or notch to pass to get to the fuel shut off position ?
It has been established that both engine propellers went into feather. We will have to wait to learn if that was caused by system malfunction, or if it was crew error when intending to reach for the Power Levers, or even for the Flap Lever, they instead reached for the Condition Levers.
Originally Posted by Sycamore
The act of unfeathering should start the engine as well..
Again, only speaking for the DH8, but every engine restart in flight required the use of the electric starter both on the -300 and -400 series. A windmill relight is no option. The propeller is only unfeathered after the engine restart has been successful and the turbomachinery is running normal again. The associated procedure is rather long (2 full pages in the QRH) and takes much longer to complete than available when already in a circling approach at rather low altitude. IŽd guess that facing such a predicament, using the available energy to glide to some sort of landable field would be the better option.
Which is of course rather academic and leaves aside the startle factor and other things on the crews mind at such a moment.
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@ Zerograv :
Not familiar with the ATR quadrant, but looking at a photo, do you mean that : 1) retarding the conditions levers to Fuel shut off would automatically feather the props and 2) there is no push or pull button or notch to pass to get to the fuel shut off position ?
Not familiar with the ATR quadrant, but looking at a photo, do you mean that : 1) retarding the conditions levers to Fuel shut off would automatically feather the props and 2) there is no push or pull button or notch to pass to get to the fuel shut off position ?
2) As you correctly mention there is a Botton that has to be used to pass it then from the 'FTR' position to the 'FUEL SO' ('Fuel Shut Off', and therefore Engine Shutdown). This is to prevent inadvertently shuting down the engine.
The Condition Lever of the ATR has 4 positions. '100 OVRD', 'AUTO' (characterised by a notch), 'FTR', and 'FUEL SO'.
In the older models (300) there is no '100 OVRD', or 'AUTO' positions, but the operation principle is the same.
That may be true with single-shaft engines like the Dart or similar, where a spinning propeller will turn the compressor as well. On the PW120 series, the propeller is not connected to the turbomachinery proper except via the power turbine. Here, unfeathering the engine will only result in drag and not in a restarted engine.
), you can in fact hold the prop of a PW120 (or PT6) while the engine is starting.
you can in fact hold the prop of a PW120 (or PT6) while the engine is starting
