ATR-72 crash at PKR, Nepal. Many fatalities feared.

[Gabriel]

What is the critical difference between a stall in level flight and an accelerated stall in a sudden steep turn?

No warning.

Wrong. Terribly, terribly wrong. The stall warning works on AoA. It activates a few degrees before the critical AoA. And you stall at the critical AoA straight and level or in a steep turn. The stall warning would activate in any case.

[3WE]

Why would an experienced pilot not pull back in a turn to final at very low altitude?

Because it’s a common cause of accidents with not_experienced pilots.

And you are in full-on black and white…the mind doesn’t say steep bank, don’t pull up…

INSTEAD:

It’s recognizing that you are getting steep so ease up on the bank, and increase the palm oil levers AND WATCH THE GD AIRSPEED and adjust further, as necessary.

[Evan]

Wrong. Terribly, terribly wrong. The stall warning works on AoA. It activates a few degrees before the critical AoA. And you stall at the critical AoA straight and level or in a steep turn. The stall warning would activate in any case.

No practical warning. Unlike in a level flight approach to stall where you have time after stickshaker to recover, banking aggressively beyond 30deg at insufficient airspeed/power and very low altitude (yes, while holding altitude, having none to give), there is not enough time and altitude to recognize and recover. In a wings-level approach to stall, the ATR can often power out of that even before the pitch reduction, losing minimal altitude. In this accelerated scenario, which goes from no warning to smoking hole in several seconds, your chances of recovery are what exactly?

So that's what I think might have happened. Even if it did, there had to have been some pilot error or mechanical failure prior to the turn.

[Evan]

And where in the hell did you get a 60 degree bank? Why not 50? 70? 63.5493?

60deg immediate turn. (approximately) Read all the words. I do not hide them in 8pt type.

[Gabriel]

No practical warning. Unlike in a level flight approach to stall where you have time after stickshaker to recover, banking aggressively beyond 30deg at insufficient airspeed/power and very low altitude (yes, while holding altitude, having none to give), there is not enough time and altitude to recognize and recover. In a wings-level approach to stall, the ATR can often power out of that even before the pitch reduction, losing minimal altitude. In this accelerated scenario, which goes from no warning to smoking hole in several seconds, your chances of recovery are what exactly?

So that's what I think might have happened. Even if it did, there had to have been some pilot error or mechanical failure prior to the turn.

Wrong at so many levels. You do have "practical warning". As you push back to try to hold the altitude the stickshaker will shake with a margin of safety before the stall. If you keep pushing back more after that, well, ask a lot of dead pilots and passengers what happens after that. If you don't keep pulling back more, relax just a little bit the back pressure, level the wings and add full power, and fly away, you never stalled and you are alive. And this can be completed in almost the same loss of altitude than a straight stall.

Wing drops have killed pilots even when they stall straight and level. Most people, including many pilots, don't understand this, but the biggest danger of a stall is not the loss of lift, it is the loss of aileron authority, loss of roll dampening, and increase in aileron-induced adverse yaw that leads to a loss of lateral control. Almost all of the stall fatalities are coupled with a loss of lateral control. Almost never the crash happens at wings-almost-level. And this combination of effects starts BEFORE the actual stall. That is why the range between the stall warning and the actual stall shall not be used.

Plus, as 3WE told you many times... There was NO steep bank, no 30deg bank, let alone "aggressively beyond 30deg", not until they lost lateral control and at that point it was the plane banking on them, not the pilots banking the plane.

And as I told you, they seem to be cranking about all the way to the right by when the bank was about just 15 degrees left.

WHAT STEEP BANK ARE YOU TALKING ABOUT?
Are we talking about the same accident here?

What happens here is that the plane stalled or was very very close to stall and they lost lateral control, rolled and crashed. Why all tat happened? I don't know. Maybe they had the AP set at alt hld or vs and didn't have enough power applied and they were not paying close attention to the speed. It would not be the first time. But a commanded immediate aggressive steep turn to final seems to be pretty much discarded even with the little information we have so far. Because there is a VIDEO if the loss of control and the video shows no such bank before they lost control.

[Evan]

WHAT STEEP BANK ARE YOU TALKING ABOUT?

This one:



Was this roll initially commanded or is it an asymmetrical stall? When does loss of control occur? How can you tell for certain? Can you really make out the ailerons? I can't.

It certainly becomes a stall immediately thereafter (Perhaps with .05 seconds of stickshaker warning, perhaps inducing them to counter with ineffective right aileron).

Wrong at so many levels. You do have "practical warning". As you push back to try to hold the altitude the stickshaker will shake with a margin of safety before the stall. If you keep pushing back more after that, well, ask a lot of dead pilots and passengers what happens after that. If you don't keep pulling back more, relax just a little bit the back pressure, level the wings and add full power, and fly away, you never stalled and you are alive. And this can be completed in almost the same loss of altitude than a straight stall.

Wing drops have killed pilots even when they stall straight and level. Most people, including many pilots, don't understand this, but the biggest danger of a stall is not the loss of lift, it is the loss of aileron authority, loss of roll dampening, and increase in aileron-induced adverse yaw that leads to a loss of lateral control. Almost all of the stall fatalities are coupled with a loss of lateral control. Almost never the crash happens at wings-almost-level. And this combination of effects starts BEFORE the actual stall. That is why the range between the stall warning and the actual stall shall not be used.

Again, you are retreading things we already know about stall.

Take off your propeller hat and put on your detective hat:

What is new here? A new airport and a new runway approach. Two weeks old. This might be the very first time this crew has flown it. So maybe that's a clue. A factor.

If I am correct about the approach involving a steep 60deg (ish) turn to final, it is a significant manuever for large transport category civilian aircraft. Why on earth would they design such an approach rather than placing the turn further out and allowing a nice 8+ mile stabilized final? Because Nepalese pilots routinely navigate winding approaches in more terrain-conflicted destinations, they would be expected to be capable of safely flying such a manuever. So why go to the expense of building new navaids when a perfectly good one is sitting at the old airport. Culture.


(The VNPK VOR is situated right next to the Mount Heaven School pin)

Now, run the scenario: Lets assume they are a bit fatigued and haven't properly briefed the approach. The crew is well-accustomed to flying the approach to land at the old airport and the speeds and altitudes they should be at along the way. Based on the passenger video they are above the old runway at maybe two hundred feet of altitude and about 1.5 miles out from the 12/30 threshold. If they don't turn (and turn sharply!) right at this moment, if they continue on their current heading, then where the hell are they going at such low altitude?

If they are shooting for 12/30, the moment you see in the image above is the last possible moment they can turn to line up with that runway.

Now what if they are flying at or near Vref (maybe even dropped below it), hadn't thought through the new approach in advance and are navigating to the detriment of aviating? And they make a steep left turn in this condition? What happens next?

Add to this any other contributing factors such as a left engine out, a rudder jam (no reports of problems thus far), misconfiguration, unforeseen human error...

It's only a theory, but it is the only one that seems to add up aside from some kind of Renslowian act of randomness (this a/c is too low for stickpusher, however).

[Gabriel]

This one:

To me, based on the dynamics seen in the video, it is very clearly that they had already lost lateral control at that point.

Was this roll initially commanded or is it an asymmetrical stall?

Initiated? I don't know.

When does loss of control occur?

I don't know the instant that out of control starts, but when they are cranking aileron and rudder right and the plane keep rolling to the left they are officially pout of control. And that, in my observation, was already happening at least a few frames before your still when the plane was at about 15 degrees of bank. I can't make the ailerons earlier than that so I don't know what happened when the roll started.

How can you tell for certain? Can you really make out the ailerons?

I believe I can make the ailerons and rudder, yes. For certain? No.

Take off your propeller hat and put on your detective hat:

What is new here?

I am afraid that probably not much. Same old story of pilots stalling, losing lateral control and crashing and dying and killing.

A new airport and a new runway approach. Two weeks old. This might be the very first time this crew has flown it. So maybe that's a clue. A factor.

If flying a new approach in severe VMC and open terrain was a risk factor, planes would be falling all the time.

If I am correct about the approach involving a steep 60deg (ish) turn to final,

Please stop mixing the heading change with the steepness of the turn. A change of 60 degrees of heading doesn't need to be steep. An approach will never call for a steep turn. If the pilots were coming to the VOR on the 360 radial, they had the runway perfectly in sight on their left and they could have started the turn as early as the wanted and make is as shallow as they wanted. Again, airplanes, including big ones, fly visual approaches and turn base to final all the time. Also many IFR approaches include 180-degrees turn.

it is a significant manuever for large transport category civilian aircraft. Why on earth would they design such an approach

I bet you a beer that the approach design did not include a prescribed steepness of the bank or radius of the turn. Have you seen planes perform turns on a navaid or fix where, in the chart, the route direction changes instantly? (zero radius). Hint, 90-degree-banks with infinite Gs are not involved. Neither in manual flight nor on AP.

rather than placing the turn further out and allowing a nice 8+ mile stabilized final? Because Nepalese pilots routinely navigate winding approaches in more terrain-conflicted destinations, they would be expected to be capable of safely flying such a manuever. So why go to the expense of building new navaids when a perfectly good one is sitting at the old airport. Culture.

Nonsense. First of all I heard that they were on a visual approach (can't confirm though). Second, I am very confident that if this runway is served by an IFR approach, said approach doesn't involve a turn 1.5 NM from the runway. Third, you don't need to move the navaid to make the final you want.

Now, run the scenario: Lets assume they are a bit fatigued

Evidence or hint?

and haven't properly briefed the approach.

Evidence or hint?

Based on the passenger video they are above the old runway at maybe two hundred feet of altitude and about 1.5 miles out from the 12/30 threshold. If they don't turn (and turn sharply!) right at this moment

If they are shooting for 12/30, the moment you see in the image above is the last possible moment they can turn to line up with that runway.

If they are shooting for 12/30, the moment you see in the image above is the last possible moment they can turn to line up with that runway.

Now what if they are flying at or near Vref (maybe even dropped below it), hadn't thought through the new approach in advance and are navigating to the detriment of aviating? And they make a steep left turn in this condition? What happens next?

IF they did that (which I have reasons to think they didn't, as per explained), don't blame "the approach" or they being new to it. They had the runway in sight. Who told them to wait so long to start the turn?

Add to this any other contributing factors such as a left engine out, a rudder jam (no reports of problems thus far), misconfiguration, unforeseen human error...

It's only a theory, but it is the only one that seems to add up

Ha! What about a meteor strike?

aside from some kind of Renslowian act of randomness (this a/c is too low for stickpusher, however).

Maybe not a fully Renslowian, but not paying attention to speed and then trying to control roll in the environment of the stall instead of recovering the stall first, is something relatively common. Variation of that can be seen in Colgan, Air France, Turkish, Spanair, Northwest (Detroit) and many, many others. In fact, there is a full dozens-page-lomng thread dedicated to stalls. Remember?

[Not_Karl]

we'll have to wait for the final report.

Concur.

[Evan]

I believe I can make the ailerons and rudder, yes. For certain? No.

I have scrutinized every image I can find from that ground view video and I see no aileron. Can you post what you are referring to?
I see what could be right rudder deflection (the absence, not presence, of the rudder in view). But this is very speculative. Low resolution artifacts are misleading.

If flying a new approach in severe VMC and open terrain was a risk factor, planes would be falling all the time.

As you know, a risk factor in itself does not usually result in any planes falling out of the sky. It needs other factors coming together to form a rare fatal equation.

I bet you a beer that the approach design did not include a prescribed steepness of the bank or radius of the turn. Have you seen planes perform turns on a navaid or fix where, in the chart, the route direction changes instantly? (zero radius). Hint, 90-degree-banks with infinite Gs are not involved. Neither in manual flight nor on AP.

I'm speculating that the approach plate (or brief) called for overflying the VNPK VOR and then turning to final, but yes, that would be a very severe turn for a standard approach. I'm also speculating that, as this pilot was in her last leg of F/O service before moving to PIC while flying with an instructor pilot on an entirely new approach, perhaps they were flying by the navaids rather than a purely visual approach. This might have distracted them from monitoring primary instruments.

But please answer this question:

Based on the passenger video they are above the old runway at maybe two hundred feet of altitude and about 1.5 miles out from the 12/30 threshold. If they don't turn (and turn sharply!) right at this moment, if they continue on their current heading, they will miss the runway, so then where the hell are they going at such low altitude?

This is what I'm stuck on. They HAD to turn there*, and sharply, or miss the approach.

*based on the position and flight path I have estimated from the two videos and satellite views of the area.

[xspeedy]

This is what I'm stuck on. They HAD to turn there*, and sharply, or miss the approach.

*based on the position and flight path I have estimated from the two videos and satellite views of the area.

I think that base leg is further east than depicted. I think they came across the northern end of the old airport runway. You can make out for just a second the very northeastern corner of the airport service road. You never see runway out the window.

[3WE]

***Please stop mixing the heading change with the steepness of the turn.***

Evan… for a person who can spew acronyms and Airbus procedures as good as ATLcrew, Bobby and Kent, when it comes to fundamentals and reality, you are firmly in the sterile bubble on this crash.

Take note of what Gabriel says here.

ALSO TAKE NOTE HOW BOTH OF US HAVE SAID THAT the plane is slow and rather level. It pulls up gently and BAM, IT STALLS WITH A SHARP, UNCOMMANDED WING DROP.

It is possible that full, corrective rudder and aileron were in play for an engine failure…don’t KNOW if that’s the case but it is consistent.

STALLS ARE PREVENTED BY GABRIEL MONITORING THE AOA INDICATOR AND 3BS MONITORING AIRSPEED AND SITUATIONAL AWARENESS AND MAKING MEASURED PULL UPS AND BOTH OF US LISTENING FOR STALL WARNINGS AND RESPONDING WITH, PROMPT, MEASURED AND CAREFULLY ADJUSTED INPUTS IN THE NOSE DOWN DIRECTION…and if I’m timely, I go to full power and a strong climb attitude as long as the stall warning is off and the plane isn’t mushing and dropping wings. And the stall warning system is a little bit robust.

Sorry, no acronyms above, but you should take a break from Airbus manuals, read this post about 100 times and go take a bike ride.

[Evan]

OK, I finally found the FULL cabin video and gave that a much closer look. So it appears to be a circle-in approach, they fly near the Bhadrakali Temple, then over the old airport threshold, in a light bank... and then the stall occurs. It seems to me that they had to tighten the bank as they came around but not so steeply as I imagined. Maybe still a factor. That definitely makes more sense.

[3WE]

This is what I'm stuck on. They HAD to turn there*, and sharply, or miss the approach.

They did not HAVE to turn SHARPLY…AND THERE IS NO VIDEO EVIDENCE OF A SHARP TURN (THE STEEP BANK WAS AFTER THE STALL.)

My local airport used to be busy and controllers would ask aircraft to make S-turns…the ATR could have overshot and calmly turned back to final…nice and stabilized.

If there was video of a steep turn you’d have something, but your protractor exercise isn’t reality…The bank you are hung up on is from the stall, not a commanded sharp turn.

[Evan]

I'm seeing it like this now. They break off the RWY30 approach and follow visual landmarks in a circle-to-land for RWY12, but need to tighten the turn right at the point where the stall occurs.

[LH-B744]

Hm. If you asked me one week ago, I had said, hey let's meet here next time to celebrate January 15th 2009. 'Give me a count.' .. '- 155.' '155?' '-Yes.' , to quote Tom Hanks, or his living prototype,
Flight Captain Chesley B. Sullenberger III. Who btw soon gives us another reason to celebrate... 70 years of aviation with Mr Sullenberger, or something like that..

But back on topic. Again, one week ago I had said, all airlines who are younger than me are to be treated with care. Not that wouldn't trust the 1990s, but in that decade here in Germany also alot of shit happened. 1994, the Gatow airfield in Berlin was closed, and so on and so on.

On German radio (!), they said that this airline has no license to fly within Continental Europe, Switzerland included afaik.
For the moment, I don't like to add a comment, here.

A/c type was an ATR72-500, so, a twin engined propeller, and in my eyes per se it isn't an unsafe a/c. So, what has happened. The airport is the newest airport which I know, open to the public since... January 1st 2023 (!) . Most of the time, it depends on the human end of the connection, e.g. also if we talk about dogs.

https://de.wikipedia.org/wiki/ATR_72

Up to 74 passenger seats, with a structural max. payload of 7050 kg, without a calculator that is less than 100 kg for one passenger, all your suitcases included.

They didn't really overload this rather small passenger a/c, 27 meters short, or what has happened?

PS: Given the magenta line which Evan has published a few moments ago, (at least) two things come to my mind.
1. If that really is a "ten suitcases too much" problem, that is also a fuel consumption problem, as I assume. As if you tried to move a payload of 1000 kg
with a 34 hp car engine. You might be able to move the car, but the engine could need 120 liters where it normally needs 12 liters of fuel.
And then I try to imagine a rather narrow corner, on final, full flaps, 1200 liters instead of 120, when overloaded? Did they run out of fuel prior to the stall?
2. Randazzo with one of his products shows me that there is something like a bank angle limiter, which can be set to 'auto' or '5' or '10' or '15' or '20' or '25' .
But without such a bank angle limiter, an ATR72-500 could be more demanding than a B744.