Accidents and Close Calls Discussion on accidents, close calls, and other unplanned aviation events, so we can learn from them, and be better pilots ourselves.

Nepal Plane Crash

Old 12th Feb 2023, 01:31
  #481 (permalink)  
 
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So that would explain the lack of noise on the ground video and no spool up of the engines to boot when you’d expect them going to TOGA.

Mix in the tight bank, the fact they had just gone to flaps 30, thats going to bleed speed real fast.

I am guessing the holes in the cheese lined up mighty quick and right at the critical time.

hopefully the initial report will shed more light.
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Old 12th Feb 2023, 08:22
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A few more thoughts on feathered propellers, if I may.

On a PW120, it is necessary to view the state of the propeller and of the turbomachinery separately, as I already hinted on previously. It is possible to have the propeller feathered or unfeathered independently of the turbomachinery running or not running, although obviously not all combinations are within the realm of the SOPs.

Let us look at the possibilities.

1. Propeller unfeathered, turbomachinery running.

This is obviously the normal operating state in flight. The engine (let me use this word in the sense of "combination of propeller and turbomachinery" from now on) will provide electric power and bleed and most importantly thrust as requested by the power levers; with the power levers in idle, some drag will be expected depending on the propeller RPM. The higher the prop RPM, the higher the expected drag in this case. This substitutes for a speed brake quite well - think shifting down on a manual gear box without pushing the gas pedal on a car.


2. Propeller feathered, turbomachinery running.

This is normal after starting the engine on ground and in flight. The engine will provide only electric power and bleed, no thrust and neither significant drag with the power levers at idle. However, in case of a feather at high power selection expect rather weird indications: torque against a feathered propeller is very high. In case of an unscheduled feather, it is thus required to apply the associated procedure to the engine showing more torque than the other one, which is a bit counter-intuitive at first and requires conscious identification of the issue at hand.

In flight, this state is achievable by either pulling the condition levers back to START/FEATHER or by hitting the alternate feather buttons that are hidden behind a transparent cover on the DH8 and probably similar on the ATR. Both selections require confirmation by the PM.

As the turbomachinery is still running, such a situation is fairly easily rectified, should it be entered by error. Pushing the condition levers forward and/or unselecting autofeather will bring the engine back to normal operating mode (prop unfeathered, turbomachinery running).


3. Propeller feathered, turbomachinery not running.

This is the normal shutdown state of the engine both in flight and on ground. There will be low drag from the failed engine and obviously no power. This condition is covered in performance calculations, trained and keeps the aircraft flyable, preferrably of course with another engine providing power.

Getting the engine to provide power again requires a normal engine start on ground which takes about 45-60 seconds or the application of the engine restart in flight QRH checklist, which takes much longer as it involves resetting various systems and getting the engine into a startable condition first. A bit more than 2 minutes may well be expected.


4. Propeller unfeathered, turbomachinery not running.

This is a rather undesired state. The engine will provide maximum drag and no power at all in flight. It is entered by various common and often-trained malfunctions like a flameout with autofeather not working; there are a few most dedicatedly non-SOP ways of forcing it via the cockpit controls as well. In addition, an intermediate state with a dead turbomachinery and an only partially feathered propeller can be achieved by misapplication of the inflight shutdown procedure: pulling the condition levers back to "fuel off" at once without additionally hitting the autofeather will leave the propeller somewhere halfway between flight range and feather while shutting down the turbomachinery.

This situation is recoverable from. The loose ends can be picked up by applying proper and trained procedures to get the engine back to the state mentioned in (3) rather quickly and possibly later to (1) - which obviously takes more time than may be available in certain flight situations.


I´m rather curious to hear what exactly has happened in the flight deck of the flight discussed here and would be surprised to learn that all SOPs have been followed to the dot...
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Old 12th Feb 2023, 09:06
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Thank you Tu.114, that was a useful summary for those of us whose long-forgotten turboprop experience is limited to RR Darts.
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Old 12th Feb 2023, 16:33
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Originally Posted by thnarg
Thank you Tu.114, that was a useful summary for those of us whose long-forgotten turboprop experience is limited to RR Darts.
HP,LP,Feather, fire/no fire
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Old 12th Feb 2023, 19:41
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Thank you Tu.114,your summary is about Dash8-400.ATR72-500 has different engine and different propeller.

Last edited by no-hoper; 13th Feb 2023 at 09:47.
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Old 13th Feb 2023, 04:07
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Originally Posted by no-hoper
Thank you Tu.114,your summary is about Dash8-400.ATR72-500 has different engine and different propellor.
I would say a P&W is a P&W. However please fill us in on the difference s
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Old 13th Feb 2023, 10:07
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PW120 and PW150 are completly different engines.You might find some common screws.
That‘s it.
PW150 is FADEC controlled,the 120 by push-pull cables.
No alternate feather buttons on the ATR.

Propellers are made by different manufactors.
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Old 13th Feb 2023, 12:14
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Tu.114
Great stuff !!!

Originally Posted by megan
With some helicopters you can start the engine with the rotor held stationary, once at idle release the rotor brake, provided rapid rotor acceleration which was useful to avoid rotor blade flapping in high winds.
That's how ATR gets away with not having an APU. A propeller Brake on the Right Engine.
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Old 14th Feb 2023, 07:56
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Originally Posted by zerograv
Tu.114
Great stuff !!!



That's how ATR gets away with not having an APU. A propeller Brake on the Right Engine.
Which some airlines don't allow their crews to use away from an engineering base
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Old 15th Feb 2023, 12:51
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Originally Posted by megan
With some helicopters you can start the engine with the rotor held stationary, once at idle release the rotor brake, provided rapid rotor acceleration which was useful to avoid rotor blade flapping in high winds.
Yes. But this procedure was also found as a reason for a crash or two of a certain U.S. Mil helicopter AFAIK. Sudden torque increase on shaft and near zero centrifugal force on blades could cause that drag brace, supporting M/R Blade in lead-lag direction, might become compressed instead of stretched during such fast acceleration - a condition, that brace might not be designed for. And repeating it may cause it to fail one day. Only a correct combination of torque and RPM increase will prevent this. I suspect some (big) propellers might have the same problem - part of pitch change bearing loaded with compression (as designed) but other side loaded in opposite direction - with loads spread somewhere else. It was often difficult to expain to some (pilots), that pulling a small airplane on the ground by grabbing a prop blade of variable-pitch propeller might not be a good idea, as pulling the airplane forward this way is entirelly different thing than pulling it thru the air with blades rotating-albeit it looks like there is no difference - at first glance.
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Old 15th Feb 2023, 14:23
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The Preliminary report is out .

https://www.tourism.gov.np//files/pu..._files/343.pdf

PRELIMINARY ACCIDENT INVESTIGATION REPORT 9N-ANC (ATR 72-212A, MSN: 754)

Alternate Link from FR24
https://www.flightradar24.com/blog/w...ary-Report.pdf

Last edited by Yo_You_Not_You_you; 17th Feb 2023 at 10:13.
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Old 15th Feb 2023, 15:13
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Some questions to those in the know.

1. On the ATR, are the condition levers and the flap lever adjacent to each other?

2. a. How are the condition levers and how is the flap lever protected against inadvertent movement?

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?

c. Are there differences between the respective levers latch types or is the required action to unlatch the lever the same on both?

d. Are there differences between ATR subvariants?
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Old 15th Feb 2023, 15:15
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Originally Posted by Yo_You_Not_You_you
https://www.tourism.gov.np//files/pu..._files/343.pdf

PRELIMINARY ACCIDENT INVESTIGATION REPORT 9N-ANC (ATR 72-212A, MSN: 754)

Not good reading
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Old 15th Feb 2023, 15:47
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That link is not giving me anything atm.

Does it hint anything as to why none of the engines were producing power? (which I got from Reuters)
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Old 15th Feb 2023, 15:52
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Whow, and less than a minute between the PF call for FLAPS 30 (56.32) and the stall (57.26 ) , Except for a mention of the brief single master caution at 56.36 . Looks like they both never realised the props were feathered and wondered why they did not get power when pushing the thurst levers.
Someone with ATR72 experience can maybe explain this sequence and unnability for the crew to notice the conditions of the props.
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Old 15th Feb 2023, 15:55
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Originally Posted by 172_driver
That link is not giving me anything atm.

Does it hint anything as to why none of the engines were producing power? (which I got from Reuters)

"The PF then called for “FLAPS 30” at 10:56:32, and the PM replied, “Flaps 30 and descending”. The flight data recorder (FDR) data did not record any flap surface movement at that time. Instead, the propeller rotation speed (Np) of both engines decreased".
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Old 15th Feb 2023, 15:57
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Here are the relevant portions of the Preliminary Report (for those who cannot access it):

"At 10:51:36, the aircraft descended (from 6,500 feet at five miles away from VNPR and joined the downwind track for Runway 12 to the north of the runway. The aircraft was visually identified by ATC during the approach. At 10:56:12, the pilots extended the flaps to the 15 degrees position and selected the landing gears lever to the down position. The take-off (TO) setting was selected on power management panel.

At 10:56:27, the PF disengaged the Autopilot System (AP) at an altitude of 721 feet Above Ground Level (AGL). The PF then called for “FLAPS 30” at 10:56:32, and the PM replied, “Flaps 30 and descending”. The flight data recorder (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. On the cockpit voice recorder (CVR) area microphone recording, a single Master Caution chime was recorded at 10:56:36. The flight crew then carried out the “Before Landing Checklist” before starting the left turn onto the base leg. During that time, the power lever angle increased from 41% to 44%. At the point, Np of both propellers were recorded as Non-Computed Data (NCD) in the FDR and the torque (Tq) of both engines were at 0%. When propellers are in feather, they are not producing thrust.

When both propellers were feathered, the investigation team observed that both engines of 9N-ANC were running flight idle condition during the event flight to prevent over torque. As per the FDR data, all the recorded parameters related to engines did not show any anomaly. At 10:56:50 when the radio altitude callout for five hundred feet3 was annunciated, another “click” sound was heard4. The aircraft reached a maximum bank angle of 30 degrees at this altitude. The recorded Np and Tq data remained invalid. The yaw damper disconnected four seconds later. The PF consulted the PM on whether to continue the left turn and the PM replied to continue the turn. Subsequently, the PF asked the PM on whether to continue descend and the PM responded it was not necessary and instructed to apply a little power. At 10:56:54, another click was heard, followed by the flaps surface movement to the 30 degrees position.

When ATC gave the clearance for landing at 10:57:07, the PF mentioned twice that there was no power coming from the engines. At 10:57:11, the power levers were advanced first to 62 degrees then to the maximum power position. It was followed by a “click” sound at 10:57:16. One second after the “click” sound, the aircraft was at the initiation of its last turn at 368 feet AGL, the high-pressure turbine speed (Nh) of both engines increased from 73% to 77%.

It is noted that the PF handed over control of the aircraft to the PM at 10:57:18. At 10:57:20, the PM (who was previously the PF) repeated again that there was no power from the engines. At 10:57:24 when the aircraft was at 311 feet AGL, the stick shaker was activated warning the crew that the aircraft Angle of Attack (AoA) increased up to the stick shaker threshold.

NOTES: (from report)

1 Once the Np of the propeller decreases below 25%, no valid data is recorded in the FDR.

2 The feathering of a propeller on the ATR72-500 can be commanded automatically by aircraft systems (with interlocks preventing dual automatic feathering) or manually by the pilot. It is usually performed when an engine is shut down so that leading edge of the propeller is parallel to the oncoming airflow to reduce drag.

3 This refers to five hundred feet about ground surface.

4 This suggests a crew action inhibiting the master caution light."
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Old 15th Feb 2023, 16:25
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Below 66% NP the ACW buses are gone.
No Warnings?

Without ACW no hydraulic power.
No Warnings ?
Without hydraulic power no flap movement.
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Old 15th Feb 2023, 18:13
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Originally Posted by 172_driver
That link is not giving me anything atm.
Unfortunately, PPRuNe doesn't allow uploading of PDFs, but the original link appears to be working at the moment.
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Old 15th Feb 2023, 19:53
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Originally Posted by grizzled
During that time, the power lever angle increased from 41% to 44%.
...
One second after the “click” sound, the aircraft was at the initiation of its last turn at 368 feet AGL, the high-pressure turbine speed (Nh) of both engines increased from 73% to 77%.
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?
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