Yeti Airlines Crash

[Boac]

Well, the prelim report raises more questions than answers. https://www.tourism.gov.np//files/publi ... es/343.pdf. LHS Captain being 'checked' into Pokhara by TC.

Either a major up-cock by LHS PF (selecting feather on both props together!) OR a major malfunction in the auto-feather system (which should prevent a 'double feather event'). What is strange is that the report (1.14 on) indicates from the CVR that there was a Master Caution alert (coincident with both props feathering) but no acknowledgement mention of it on the CVR! PF then states that there is 'no power' coming from the engines.................. What was PM doing.......? Certainly not 'M'.

Since there has been no immediate engineering action I guess we have to assume cause 1?

[Fox3WheresMyBanana]

Gone in 60 Seconds
n.b. one edit of picture

The PF called for Flaps 30 at the end of the downwind leg.
The PM (who was the Instructor Captain) called "Flaps 30 and descending". However, the flaps didn't move and both engines went to feather.

Cockpit centre console pic, prop controls next to flap controls.
https://i.pinimg.com/originals/ed/5f/4b ... 1a8e0b.jpg

So, the Instructor captain
a) repeated the instruction but did NOT look at the flap indicator despite saying "..and descending"
b) moved the prop controls rather than the flap controls.

It is notable that the Flap 30 angle is almost identical to the Prop Feather angle.

The caution about the feather is not noticed as the Before Landing checks are in progress
The loss of thrust is initially not noticed because of the commencement of the descent turning base

24 seconds (after props feathered): The PM selects Flap 30 without telling the PF, and without checking around to see what lever(s) he did move earlier.
I would guess that, subconsciously, the PM assumed he'd only moved the Flaps to 15 when he thought he'd moved them to 30.

35 seconds: the PF notices there's no power and calls it.
39 seconds: (Presumably the PM) moves the power levers up to full power in two stages

They are obviously still working under the mental assumption that the prop controls haven't been moved.

45 seconds: The final turn (onto runway heading) is commenced at 368 feet
46 seconds: The PF gives control to the PM and repeats that there is no power.

52 seconds: stick shaker
54 seconds: second sticker shaker and aircraft flicks left in the stall
60 seconds: ground impact.

[TheGreenAnger]

Gone in 60 Seconds

The PF called for Flaps 30 at the end of the downwind leg.
The PM (who was the Instructor Captain) called "Flaps 30 and descending". However, the flaps didn't move and both engines went to feather.

Cockpit centre console pic, prop controls next to flap controls.
http://www.mutleyshangar.com/reviews/ro ... destal.jpg

So, the Instructor captain
a) repeated the instruction but did NOT look at the flap indicator despite saying "..and descending"
b) moved the prop controls rather than the flap controls.

The caution about the feather is not noticed as the Before Landing checks are in progress
The loss of thrust is initially not noticed because of the commencement of the descent turning base

24 seconds (after props feathered): The PM selects Flap 30 without telling the PF, and without checking around to see what lever(s) he did move earlier.
It is notable that the Flap 15 angle is almost identical to the Prop Feather angle. I would guess that, subconsciously, the PM assumed from muscle memory that when he moved the props to feather, he'd only moved the Flaps to 15.

35 seconds: the PF notices there's no power and calls it.
39 seconds: (Presumably the PM) moves the power levers up to full power in two stages

They are obviously still working under the mental assumption that the prop controls haven't been moved.

45 seconds: The final turn (onto runway heading) is commenced at 368 feet
46 seconds: The PF gives control to the PM and repeats that there is no power.

52 seconds: stick shaker
54 seconds: second sticker shaker and aircraft flicks left in the stall
60 seconds: ground impact.

A likely scenario. One would have thought that given the proximity of the prop lever and the flaps lever there would be some of detent (or pull up and over) on the feather position to stop this kind of mistake? Where are the resident ATR pilots here? Would there have been an aural warning as well as the red light on the Master Caution Display when both props were feathered?

[Fox3WheresMyBanana]

please note the initial pic posted was wrong, I've changed it.

I think the basic problem is that the PM, the Instructor Captain, is struggling to see the runway from the RHS on a LH circuit.
It's a high wing aircraft using up to 30 degrees of bank in a tight circuit surrounded by mountains.
If he's leaning across a bit, this would account for grabbing the wrong levers. He did it by muscle memory and not by looking.
It also explains why his attention is out of the cockpit, and he's just doing the mouth music and not looking at the gauges (we know this from the "and descending" call)

The PF is obviously focused on doing her PF bit perfectly as it's her final checkride before captaincy. She's not thinking of the PM as a nugget first officer, because she knows he isn't, and presumably assumes he won't be doing anything deliberately wrong at this stage because it would be risky.

[Boac]

A good analysis, but it begs the question as asked by TGA - SURELY there is a baulk on the prop lever to prevent inadvertent feather. I cannot understand your 'muscle memory', however, as the two actions are quite different, and if there is (hopefully) a lever or 'lift' required to move to feather that should override any 'muscle memory', since it does not exist on the flap lever. The big problem here is why the M Caution went uncommented. That is PM's job.

[Fox3WheresMyBanana]

I have reviewed the systems video, and there's no mention of a detent or lift (there is a lift required to move the power levers into reverse thrust). There's no mention of a detent in the stuff I've read online either. We'd need a comment from someone type-qualified.
..and don't call me Shirley
Muscle memory involves the cerebellum and basal ganglia, and sends nerve signals to the muscles to repeat position changes and strength inputs that have been previously learned by practice. It's subconscious.
It's also relative. The signal to move the flap lever is an angular change signal to the shoulder and subsequent muscles down the arm, from the resting position of the trunk.
So, if the trunk resting position is different, because the PM was leaning over left for better visibility, the position the arm moves to will be different, even though the change from arm to trunk is the same.
This is common when drivers look over their shoulders and move their shoulders whilst driving, and end up steering in the direction they are looking. We had it drummed out of us as baby fighter pilots, because we are always moving our bodies around, not just our heads, for better lookout.
From my personal observations of mistakes in simulators and in sports coaching, if an action requires movement of major muscles like the shoulder, and smaller muscles like the fingers, and the action does not produce the expected result, then the major movement 'wins', and the subconscious brain will change the minor movements to produce something close to the remembered effect. In practice, this means the person will fiddle with the lever in their hand rather than change the lever being fiddled with. Any detent, lifts or whatever will not stop the subconscious brain putting the lever it thinks is right into the angular position the actual correct lever should be in.This extends even to switching things off that should be on. The remembered signal is effectively not "Turn this switch ON" to the muscle memory - it has no concept of ON - but "move finger to this relative position to the body and change the switch position". And if the switch was already ON, say from some previous, unusual drill, or something the engineers did in the cockpit as part of a rare test, then the muscle memory will now turn it OFF, because that's the only position change possible. I read about exactly this in an accident report.
It's why I think it's important that the prop control feather levers angle is almost identical to the Flaps 30 lever angle. The muscle memory would have achieved the desired angular position for the lever. Note also the configuration of the grips for the flap lever and prop control levers. The flap lever is probably normally moved with first and second fingers, in this case with the actual vertical bit of the lever between the two fingers. However, the prop controls can also be moved by first and second fingers of the left hand, except now the second finger would rest on the left prop control, and the first on the right. In other words, the two prop controls can be moved by the exact same grip as the single flap control.
In good cockpit design, all the different types of controls have odd and differently shaped buttons, lozenges, grips, etc, to try to prevent this. This doesn't look cool and modern though, so I guess the designers at ATR went for style over function.

[Boac]

Found this short video which suggests a baulk on Feather. As you say, we need an ATR pilot.



We still come back to the uncommented Master Caution.

[Fox3WheresMyBanana]

Looks like there is a locking detent.
As I said - and this is my own experience and theorising not anything official or well researched - I have found that people will, if they are using muscle memory subconsciously, do what's necessary to move the lever rather than change the lever.

The master caution would appear to have been cancelled immediately, since it only chimed once.
My first guess would be that they might have been expecting a caution for some reason...autopilot disengagement?

I'm going to take a guess that the PM was overloaded mentally and canceled it without noting it.
I wonder how many times either of them had done this approach, given the airfield only opened two weeks before?

[Boac]

It certainly looks as if the PM selected double feather when PF called for Flap30 and the chime was presumably for loss of torque. The flap was not selected for over 20 seconds after the call. I suspect we will never know why this happened or why PM, particularly as a TC, did not instantly realise his mistake when he finally made the flap selection. So sad.

[Fox3WheresMyBanana]

I've never been a TC. My only experience of flight instruction was in light civvy singles, which was nowhere near my mental limits, and nowhere near as hard as doing a airline checkride into a new airport in the Himalaya.
I agree it's all very sad.
Looks like a HF mental overload situation for the TC.

[TheGreenAnger]

Seems highly likely that that TC/PM inadvertently feathered both props, did not respond to, and cleared the Master Caution light and chime, and did not respond to the PF's warning of no power/torque. Her, the PF's, continuing lack of immediate response to an escalating bad situation after the power was increased by PM, but speed was still dwindling was probably down to the authority gradient in the cockpit and the fact that she was effectively under test at an unfamiliar airfield in difficult Himalayan conditions.

Auto-throttle would not have feathered both props and was set/designed to operate at take off only.

[Boac]

Until the full report (possibly) finds the answer -

Auto-throttle should not have feathered both props and was designed to operate at take off only.

[TheGreenAnger]

Until the full report (possibly) finds the answer -

Auto-throttle should not have feathered both props and was designed to operate at take off only.

What, you mean technology goes wrong, goes wrong, goes wrong?

[Boac]

No, neber of course.

[Boac]

If the 'mechanism' for delatching the flap lever AND that for delatching the C levers is the same we have a classic 'Murphy'.

In post#21 I said

I suspect, however, this is not a 'flap' issue.

Ironically I may well be proved wrong.

[Fox3WheresMyBanana]

after the power was increased by PM

The power levers were moved up, but with the props feathered there was negligible power increase.

[TheGreenAnger]

after the power was increased by PM

Ah you are a sea lawyer. The power lever was pushed forward then, with a negligible increase in thrust to due to the feathered props (using one lever per engine) in this case if you will.

Less levers meaning the ability to really screw it up faster by pulling both into the feathered detent.

In my light piston (6 levers) twin world one reduces or increases manifold pressure by pulling the throttle control backward or forward, assuming a suitable mixture control setting for the manifold pressure setting, given altitude, ambient temp etc. One can increase or decrease the power available by juggling the black and red levers, but one uses the pitch control to make the most efficient use of the power available to produce thrust given the manifold and mixture settings. Clearly a feathered prop (lowest pitch) produces little or no thrust, while reducing the drag of a windmilling prop by effectively stopping it preferably, blade on, into the slipstream.

If I thought I had lost an engine (dead leg, dead engine) I would retard the throttle (less power) of the supposed failing engine and listen for a change of engine tone and checking any changing strain of quivering pressure required from my spindly leg on the other side of the supposed failed engine! Without any change in tone and pressure I know I am probably dealing with a windmilling engine and can set up securing it i.e. pulling the power lever fully back, closing the mixture, and moving the pitch lever into the feather detent). I have had reason to do this for real only once. Heaven forfend that one would have to do it for both, not least because this modus operandi would not really work for two as the manifold pressure and rpm gauges would be barely changed and there would be little to choose from reference leg pressure, all this while the airspeed slipped away!

[Fox3WheresMyBanana]

I didn't get my multi-engine instructor rating, and most of us instructors didn't. If the student panics during engine out training, the consequences can be fatal.

In my civvy twin training, and my RAF single piston training, in their situation of unexplained loss of power at low altitude, I was taught to shove all the engine levers fully forward (and switch the fuel tank selector, if fitted, to Both/All). This would have solved their problem. It catches most of the possible HF errors

[PHXPhlyer]

From AV Hearald:

http://www.avherald.com/h?article=503c63e9&opt=0

By Simon Hradecky, created Sunday, Jan 15th 2023 08:11Z, last updated Wednesday, Feb 15th 2023 17:36Z


On Feb 15th 2023 Nepal's AAIC (Aircraft Accident Investigation Commission) released their preliminary report summarizing the sequence of events:

On 15 January 2023, an ATR 72-212A was operating scheduled flights between Kathmandu (VNKT) and Pokhara International Airport (VNPR). The same flight crew operated two sectors between VNKT to VNPR and VNPR to VNKT earlier in the morning. The accident occurred during a visual approach for runway 12 at VNPR. This was the third flight by the crew members on that day. The flight was operated by two Captains, one Captain was in the process of obtaining aerodrome familarization for operating into Pokhara and the other Captain being the instructor pilot. The Captain being familarized, who was occupying the left hand seat, was the Pilot Flying (PF) and the instructor pilot, occupying the right hand seat, was the Pilot Monitoring (PM).

The take-off, climb, cruise and descent to Pokhara was normal. During the first contact with Pokhara tower the Air Traffic Controller (ATC) assigned the runway 30 to land. But during the later phases of flight crew requested and received clearance from ATC to land on Runway 12.

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 condition. 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 heard. 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 highpressure 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.

At 10:57:26, a second sequence of stick shaker warning was activated when the aircraft banked towards the left abruptly. Thereafter, the radio altitude alert for two hundred feet was annunciated, and the cricket sound and stick shaker ceased. At 10:57:32, sound of impact was heard in the CVR. The FDR and CVR stopped recording at 10:57:33 and 10:57:35 respectively.

Pokhara's new International Airport was opened on Jan 1st 2023 to replace the old domestic Airport.

The position of the crash site according to the preliminary report: N28.1975 E83.985

PP

[TheGreenAnger]

I didn't get my multi-engine instructor rating, and most of us instructors didn't. If the student panics during engine out training, the consequences can be fatal.

In my civvy twin training, and my RAF single piston training, in their situation of unexplained loss of power at low altitude, I was taught to shove all the engine levers fully forward (and switch the fuel tank selector, if fitted, to Both/All). This would have solved their problem. It catches most of the possible HF errors

The push the engine levers plus blue levers forward is a technique I was taught until a very good pilot I know showed me what can happen if one tries that too close to Vmc and you are not prepared to counter the rapid yaw that might ensue, particularly with the critical engine out and the good engine providing full power... although I agree there are times when it makes sense to go the push it all forward and try not to kiss you tush goodbye route.

Anyway this doesn't add any value to the Yeti conversation, so I will my feather my prop for the moment and await further reports in this sad case.