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 19th Jan 2023, 14:46
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Originally Posted by michaelbinary
Use this link https://earth.google.com/web/@28.201...9.58734423t,0r
to bring up google earth.
you are above the old airfield with the new airfield top right
move yourself over the new airfield.
use the keys to do a 360 rotation and you will see why it was a circling approach, it doesnt leave a lot of room for 5 mile finals.
google earth is really cool for this sort of perspective.
In fact I remember reading that, due to terrain considerations to the west, neither landing on 12 nor departing on 30 is available to anything much bigger than an ATR.
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Old 19th Jan 2023, 15:21
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There have been some strange crashes recently, Bangla and the Pakistan Airbus spring to mind. No one could with any certainty have predicted what the accident investigators would uncover there. In this case whilst we don't yet know what directly caused the accident, quite a number of facts are emerging. This is reported to be a tricky airport, probably what we would refer to as a Category C field, requiring special qualification. Often this involves simulator training followed by one or more landings supervised by a trainer. However in this case the airport is only a few weeks old and there is a good chance it is not yet included in the latest simulator database, nor that the trainer had necessarily flown this particular approach before. This is all informed supposition rather than fact. But the potential for the holes in the Swiss cheese to line up is there. There is no word yet who was flying. Maybe the trainer was demonstrating how he thought it should be done. Maybe the new captain was flying. In any case it is fact that the speed was allowed to decay and the aircraft departed controlled flight too low to recover. Quite why that happened will almost certainly be revealed by the investigation. With the terrain, unusual track and speed there may well have been a number of warnings going off simultaneously. Too low terrain, pull up, woop! woop! speed, speed accompanied by the stick shaker are not an unlikely combination. Sensory overload does strange things and whilst it is hard to imagine an experienced crew crashing a serviceable aircraft it cannot be excluded at this stage.
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Old 19th Jan 2023, 15:32
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Immediate left turn taking off from old airport

Originally Posted by DaveReidUK
In fact I remember reading that, due to terrain considerations to the west, neither landing on 12 nor departing on 30 is available to anything much bigger than an ATR.
As a pax I was on board a Buddha Air ATR72 taking off from the old airport, and had watched dozens of other aircraft movements whilst waiting to board. Most notable is that my and all the other aircraft commenced a left turn literally seconds after becoming airborne. There are high mountains straight ahead, and of you are in the left seat, within moments you are looking down the full length of the runway you’ve just departed. Most of the full length of the runway was used for take-off and the ascent was “positive”.
The pilots of the ill-fated Yeti Air ATR72 would have had no room to stabilise straight ahead, they were obliged to maintain a circling approach. Their only option might have been to widen it a little and GA parallel to 12 of the new airport. There was no way they were mistaken about the airport at the moment of the accident, though there might •possibly• have been a temporary confusion leading up to it if aircraft had been allowed to go lower and slower than it should.
My observation as a pax on ATRs is that once flap 30 is set (numerical marking visible to pax by window) the aircraft is pushed well nose down for final part of approach, on occasion arriving over runway with some floating, and very occasionally with a bump after ballooning during the float. In my experience some of the best landings have been achieved during very strong tricky winds, where pilots become really focussed. It seems the aircraft favours a good strong headwind component for the perfect touchdown.
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Old 19th Jan 2023, 16:14
  #304 (permalink)  
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Originally Posted by scifi
Are there any Approach Plates for this airfield...?
I just wonder why a commercial airplane carrying 70+ persons should be doing a 90 degree intercept to a 1 mile final. Has the concept of a 'Stabilised Approach' been forgotten in this case..?
Basically yes.
Welcome to Nepal . All Domestic operations are VFR, including those of the ATRs.
Approach plates ? : The last Nepalese AIP version avail on line ( April 2022) does not have the new airport in . For the old airport ( still in ) the only approach charts avail were the holdings ( 6 DME east or west at 4000 and 4500 Ft ) and an helicoper routes /reporting points. chart , That was it. Not sure what the situation with the new airport is . I worked there and flew in/out and around VNPK myself VFR in a SEP but that was 10 years ago. Probably the easiest airport to fly in in whole Nepal as it is relatively low ( 2600ft) flat all around and there was no smog/pollution so visibility was always good, unlike Kathmadu. . Sometimes Fog because of the nearby lake in early morning . . The 3 Anapurnas are just North but far enough not to affect the airport.
Now about stabilized approaches ? not in the Nepalese environment. . large turns 1 mile out is common in other airstips in the country to avoid terrain or downdrafts.
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Old 19th Jan 2023, 16:33
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Originally Posted by barrymung
I completely realise there have been no recorded incidents of mobile phones bringing down an aircraft, but
Interesting that the one incident involved a DVD player, not a cell phone. Seems the problem is not wireless transmission on a dedicated band, but just general RF interference from the electronics.
I'm also pretty sure that laptops exist that have all the capabilities of a smartphone, including cell reception.
I don't deny the potential for interference with plane systems, at least in theory, but isn't it illogical to single out mobile phones over other devices?
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Old 19th Jan 2023, 18:31
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While this is comedy it does raise several interesting points regarding electrical interference on aircraft.
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Old 19th Jan 2023, 19:26
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Originally Posted by Consol
Better not fly into Nice then. (Okay, a bit more than a mile there). Avoid JFK Carnarsie approach, the visual break off for 30 at KIAD and 34 in Salzburg.

It's called a circling approach.
What a sheltered life some lead. Add Funchal ~ Madeira Airport to the list of interesting places to operate into. 😉
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Old 19th Jan 2023, 21:57
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And we oldies remember

The old Hong Kong, NDB route (before IGS) with something like 145 degree turn at rather less that a mile ! What fun!
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Old 19th Jan 2023, 22:40
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To my knowledge, EMI from on board electronic devices has been found to be *detectable* in aircraft electronics, but has never been found to be the cause of an unexpected event or anomaly.

A reasonably thorough investigation of possible EMI was conducted for Quantas 72, which experienced uncommanded pitch downs. Proximity to a naval base with a high power transmitter was investigated as well as an assortment of on board devices. The detailed results, I can't find (probably in an appendix somewhere), but the accident report summarizes the results on pages 3-4. There was no finding of any anomaly resulting from EMI.

airsafe.com/plane-crash/atsb-qantas-a330-interim-report2.pdf

Over the years, cell phones radiation has been generally reduced and bands have changed with each new "generation."
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Old 19th Jan 2023, 23:31
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I did some basic image analysis of the twitter video. I took an image of the plane from the first frame and then 2 seconds later. I used the vertical rebar coming out the the concrete pillars to superimpose the 1st frame on the 2 seconds frame. As the camera was in motion, the alignment is very close but not exact.

Then I measured the length of the fuselage and marked off that distance increments to the later frame image. I did not account for the later image being closer and that will skew things a very small amount.

As noted on my image, I calculated that the speed of the plane was around 92 knots, ground speed. I'm guessing a bank angle of less than 20 degrees and that would change the stall speed by only a few percent.

I encourage others who can enhance the images to get better results.

Images from Twitter video
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Old 19th Jan 2023, 23:59
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Originally Posted by EXDAC
Does it make more sense if the correct case is used? If you have a web browser try a search for "Vmc roll". Vmc - airspeed minimum controllable (air).
Never come across vmc (sic) other than as vis. met. conditions but that's universally rendered as VMC. The asymmetric case has always been (and is only) Vmca or Vmcg. It would make complete sense if the correct acronym was used...and none at all when it isn't! Uncapitalised 'vmc' - and missing the a or g is a meaningless acronym. Even so I've never come across the result of exceeding that limit having a name, nor ever imagined it needed one. Is this a US expression? It certainly isn't widely known in UK or European aviation.
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Old 20th Jan 2023, 00:19
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Originally Posted by barrymung
I completely realise there have been no recorded incidents of mobile phones bringing down an aircraft, but:



Could a mobile phone have caused an erroneous reading from the AoA sensor?
Source:
https://en.wikipedia.org/wiki/Mobile_phones_on_aircraft
Contrary to one AAIB report a short while ago, a number of aircraft built before 2000 can have anomalies from the use of cell phones, particularly when they were analogue types. I had fire warnings on both engines, AP, ATR drop off because a pax in 2E in J class was trying to phone home with a Motorola Mitac, many years ago. We actually got it turned off, then back on and then off and the symptoms followed the cabin crews selection of the phone mode. Was interested when the AIB years later stated they have never had a case of interference...

In this case, No.

The ATR will use sensed AOA from a AOA vane to determine stall warning and stick shaker activation, but had the warning been suppressed, it still needs an approach to a stall to have occurred, so it would not be the initiating event. On the stick pusher, the system would have been inhibited at the time, which is a curious bit of interpretation of the rules if true. AOA would not have been causal.


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Old 20th Jan 2023, 00:36
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Originally Posted by parkfell
What a sheltered life some lead. Add Funchal ~ Madeira Airport to the list of interesting places to operate into. 😉
Shetland (Sumburgh) has a circling approach too, high bluff close to runway.
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Old 20th Jan 2023, 00:53
  #314 (permalink)  
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Originally Posted by safetypee
fdr, … yes

The stick shaker comment is also very interesting. Such a change in normal operation should have been justified by a discoverable a certification deviation.
An alternative might be a misinterpretation of changes required by retrospective inflight icing requirements; advanced, re-datumed alerting.

Any ATR operators able to confirm the stick shaker operation in these circumstances.
The Roselawn ATR42 bingle certainly added to the knowledge base on icing, and there have been some excellent advances in modelling, particularly north of the border of the US of A. The USA however, in spite of having an excellent National Resource for Icing, (Bond, "not James" Bond) has not moved out of the dark ages. The LEWICE code is no longer supported, by NASA Lewis, and was of marginal benefit. The ANSYS Canada FENSAP-ICE provides excellent solutions for ice accretion, that a number of us that have to deal with SCLD, Runback and just everyday icing issues really would appreciate the FAA updating their calendar to the 20th century. Even the boys from Seattle, last time I spoke with them, would appreciate acceptance of the code validation that has been given for years. Havent looked at this for a couple of years, so hopefully sanity prevailed.

In this event, there is no direct indication of icing being a factor, based on the video evidence, but that is not to say that the plane had encountered icing previously and was carrying a load, that would be very consistent with the event. A spectral analysis of the SPL of the video in the cabin might be interesting, the CVR spectral and the FDR should give very good indication if the wing was clean or not. If it was contaminated, particularly the tail plane, then the flight dynamics would be very close to that in the video. I doubt that is the case, but it can only be excluded by the FDR or the CVR spectral. The crew comments may be pertinent, but historically the crew are the last to be aware of the effects of ice in spite of being first to the accident scene.

JD used to do an excellent presentation on icing, including SCLD, and tail icing. The latter is a niche field that is starting to get lean on expertise remaining in the field, and the history of development is that it can bite. FENSAP-ICE is at least a tool to help teams from getting out of sorts.

refer §25.1419, App C to §25, App O to §25...






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Old 20th Jan 2023, 04:07
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From the two photos it seems flaps are in the process of extending, wonder if that may have anything to do with the departure eg tailplane ice? Thoughts fdr?




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Old 20th Jan 2023, 05:08
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Theres a lot to unpack, especially with all the unecessary video posts.

"On the crash - the comment by B0OM is helpful. One question I would add: given how common you say the situation is, is there a risk of alarm fatigue with the stick shaker? How often in a pilot's career might they have the shaker activate? And what does the stall recovery procedure say to do with the flaps?"

I'd honestly say I don't know (or have seen or meet) an ATR pilot who is unaware the stick shaker has activated. It's a rather intense shaker and if crews are capable and trained correctly the muscle memory should take over and they will push. Regarding flap selection.......if clean the memo items call for Flap 15 if you have Flap 30 it stays there until the clean up post event.

Reagrding Vmca.......an ATR with an active shaker or pusher will go off well before Vmca is reached in a single engine situation. In fact to get the machine to perform (demo) the Vmca you have to deactivate the shaker and pusher and take it almost to the point of stalling. Apart from demonstration in a sim during training I have never witnessed a crew get even close to Vmca.

To the comments regarding tail plane ice. My understanding is the flight was conducted in VMC and there was no icing. If there was icing and it was bad enough to develop tail plane icing the crew would have encountered severe ice and therefore the SEV ICE memo items and checklist. That checklist limits flap to 15 for approach and landing which increases your approach speed significantly and then another factor is applied meaning you'll get nowhere near your stall speed (comment: no ATR crew in their right mind would do a circling approach after a severe icing event unless there was no other option anywhere).

If as someone suggested the ground speed was around 92 knots, this ATR was unbeliveably slow for a flap 30 config, let alone a flap 15 config. Conservative manoeuvring speeds for the ATR are 180 KIAS clean, 150 KIAS Flap 15 and Gear and 130 KIAS Flap 30. Minimum speed is 95 KCAS (period) and you'll only get close to this on an empty aircraft with no wind. The Yeti aircraft was pretty full, some basic math.............ATR empty weight 13800 kg (with crew), 68 pax with bags = 6800 kg so ZFW = 20600 kg (only 2400 kg away from MTOW if it was the 23000 kg variant). I don't know the fuel they had on board so lets just say they had a landing weight of 21000 kg. Below is the base performance data
VmHB 30 (Vref) = 107 kts
Correction = 1/3 headwind or all of the gust and that will give the Vapp. Most airlines use a stabilsation criteria of Vapp 0 - +10 some use 0 - +20
Vs Flap 30 and Gear down at 21000kg is approximately 87 Kcas
Vs Flap 15 and Gear UP at 21000kg is approximately 97 Kcas
As you may or may not see ATR gives crews approximately a 1.23 buffer (23%) Vref over Vs, its concievable if you have a 10 knot headwind that the Vapp will increase to 110 KIAS moving you further from stalling.
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Old 20th Jan 2023, 05:55
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Originally Posted by theFirstDave

Then I measured the length of the fuselage and marked off that distance increments to the later frame image. I did not account for the later image being closer and that will skew things a very small amount.



Images from Twitter video
That method would work if the plane was flying directly across the field of view but not in this case where it is approaching at an angle.

Just imagine the answer it would give if the flight was directly towards the camera?


So I'd say you need to multiply your answer by 1/sin(45 degrees) to allow for the angle (guessed at 45 degrees)

which would give 92 x 1.414 = 130 knots

Also the fuselage is 1.5 times as long in the second image as the first, so the skew may not be negligible.

Last edited by netstruggler; 20th Jan 2023 at 07:29.
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Old 20th Jan 2023, 06:12
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Originally Posted by GALWC
The old Hong Kong, NDB route (before IGS) with something like 145 degree turn at rather less that a mile ! What fun!
You might want to check your facts, even though you may think it sounds impressive to make up and post whatever numbers come into your head.

The actual figures were a 47 degree turn commenced at 2DME.

Last edited by pilotmike; 20th Jan 2023 at 07:55.
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Old 20th Jan 2023, 06:19
  #319 (permalink)  
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Originally Posted by megan
From the two photos it seems flaps are in the process of extending, wonder if that may have anything to do with the departure eg tailplane ice? Thoughts fdr?
Flap extension is the most problematic time for a tail plane icing event. The conditions suggest at least the last part of the flight was in VMC, what conditions existed before that BO0M has commented on. Not that long ago, right over the top of Kunming, in winter doing one of their interminable arrivals, we descended through some some interesting AS, the kind you like to see in the ski season, but not in a plane. NAI went on before entry, and we had a camera running. We picked up 3/4" of ice in 5 seconds. In 28,000 hours of driving, have never seen ice pick up that fast. Point is, there are conditions that may seem benign, and result in severe ice accretion. If that happened, it would be discernible in the FDR data as a rapid change in the drag polar, and where there may be GPS data, then the change in CL can be quickly determined. Did that happen? Hard to say (easy to drink... Johnny Walker) The data will rule it in or out.

On the SEV ICE memo, there are a lot of natural cues that a plane is carrying ice, if the crew are interested in the proceedings, I am not sure that i have ever had any alert system that has not given erroneous data at some point... Would hope that peeps driving "plains" are never basing their continued happiness and well being on any single source being good.

Originally Posted by BO0M

"On the crash - the comment by B0OM is helpful. One question I would add: given how common you say the situation is, is there a risk of alarm fatigue with the stick shaker? How often in a pilot's career might they have the shaker activate? And what does the stall recovery procedure say to do with the flaps?"

I'd honestly say I don't know (or have seen or meet) an ATR pilot who is unaware the stick shaker has activated. It's a rather intense shaker and if crews are capable and trained correctly the muscle memory should take over and they will push. Regarding flap selection.......if clean the memo items call for Flap 15 if you have Flap 30 it stays there until the clean up post event.

Reagrding Vmca.......an ATR with an active shaker or pusher will go off well before Vmca is reached in a single engine situation. In fact to get the machine to perform (demo) the Vmca you have to deactivate the shaker and pusher and take it almost to the point of stalling. Apart from demonstration in a sim during training I have never witnessed a crew get even close to Vmca.

To the comments regarding tail plane ice. My understanding is the flight was conducted in VMC and there was no icing. If there was icing and it was bad enough to develop tail plane icing the crew would have encountered severe ice and therefore the SEV ICE memo items and checklist. That checklist limits flap to 15 for approach and landing which increases your approach speed significantly and then another factor is applied meaning you'll get nowhere near your stall speed (comment: no ATR crew in their right mind would do a circling approach after a severe icing event unless there was no other option anywhere).

If as someone suggested the ground speed was around 92 knots, this ATR was unbeliveably slow for a flap 30 config, let alone a flap 15 config. Conservative manoeuvring speeds for the ATR are 180 KIAS clean, 150 KIAS Flap 15 and Gear and 130 KIAS Flap 30. Minimum speed is 95 KCAS (period) and you'll only get close to this on an empty aircraft with no wind. The Yeti aircraft was pretty full, some basic math.............ATR empty weight 13800 kg (with crew), 68 pax with bags = 6800 kg so ZFW = 20600 kg (only 2400 kg away from MTOW if it was the 23000 kg variant). I don't know the fuel they had on board so lets just say they had a landing weight of 21000 kg. Below is the base performance data
VmHB 30 (Vref) = 107 kts
Correction = 1/3 headwind or all of the gust and that will give the Vapp. Most airlines use a stabilsation criteria of Vapp 0 - +10 some use 0 - +20
Vs Flap 30 and Gear down at 21000kg is approximately 87 Kcas
Vs Flap 15 and Gear UP at 21000kg is approximately 97 Kcas
As you may or may not see ATR gives crews approximately a 1.23 buffer (23%) Vref over Vs, its concievable if you have a 10 knot headwind that the Vapp will increase to 110 KIAS moving you further from stalling.
As a profession we seem to "double cross the bridge" on stalls and our responses to that. Seems a tad untidy, and is hardly well received by the self loaders that pay our bills. A stall is not something that we should be fearful of, even in a T tail, like the B727, Cl600 or a Lear, or an ATR, stick pusher or not. Even a Trident getting parked vertically at Staines. Yes, if you abuse the plane for long enough it will get bitey, and the recovery from that, while quite possible needs a chunk of airspace between the pointy bit and the hard lumpy bits. The F-102 is about the most notable exception to that statement, it goes from tidy to untidy really really quickly. Still has to be abused, but, golly. The Staines, BAC 1-11, B-727 accidents wee all held in the condition by the crews for longer than the plane was prepared to put up with. Don't go out and stall the planes for the heck of it, the loads imposed on the tail alone are reason enough to avoid that, but the aircraft will stall, and will still respond correctly to controls for a period of time, relaxing back pressure will break a stall, up until the point that the stall has been abused so far that the bark turns to bites. The thrust line of the ATR should provide a nose down pitching moment on application, however, as that also blows the inner wing and flaps that can become a skosh non linear. The blowing effect assists in attaching flow over the flaps at larger angles which increases lift but also increases the Cm, the downwash increase induces flow at the tail that tends to increase the nose up moment from the tail, and that can become a bit of an issue, what controls is dependent on the tail volume, arm and the geometry of the stab relative to the engines...

FDR

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Old 20th Jan 2023, 06:22
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Originally Posted by meleagertoo
Never come across vmc (sic) other than as vis. met. conditions but that's universally rendered as VMC. The asymmetric case has always been (and is only) Vmca or Vmcg. It would make complete sense if the correct acronym was used...and none at all when it isn't! Uncapitalised 'vmc' - and missing the a or g is a meaningless acronym. Even so I've never come across the result of exceeding that limit having a name, nor ever imagined it needed one. Is this a US expression? It certainly isn't widely known in UK or European aviation.
I'd understood Vmc was the lower of either Vmcg and Vmca, because trying to continue into the air when slower than either Vmcg or Vmca will be a bad day. So using Vmc as the lower of the two gives the actual limiting speed. Maybe best let John Tullamarine settle it:

Originally Posted by john_tullamarine
Vmc and Vmca generally used interchangeably ...
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