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Nepal Plane Crash

Old 22nd Jan 2023, 18:48
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Originally Posted by guadaMB
The CVR was going to be analysed in Kathmandu.
After almost a week of the recovery, no leaks, no gossips?
There only two CVR playback facilities in Nepal (the regulator has no such internal capability). Yeti has one and Buddha has one. For obvious reasons the panel doesn't want to use the one at Yeti. For less obvious reasons they aren't comfortable using the one at Buddha. Some are suggesting it should go to France, or perhaps has gone to France already.
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Old 23rd Jan 2023, 07:05
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Originally Posted by punkalouver
Wasn’t the ATR a reversal situation or a case of aileron snatch. I thought it was the latter. Will have to re-read the Indonesian 737 report as I don’t remember that issue (or is it hidden away in an annex).

Would like more detail on the Saab issue.
Good point. Roselawn was a hinge moment reversal that gave aileron snatch. The Indon event, it isn't noted in the report but is in the dataset, and shows a point were the wing became distorted from the aileron moment, and the aircraft rolled in the opposite direction. At that point it was still in one piece, not long after it wasn't.

The hinge moment is AOA dependent, and the ATR didn't much like the AOA that it was forced to. The pressure distribution on the wing in general from runback doesn't help at all, and does impact the effectiveness of the TE down aileron. The moment change however drove the aileron to command a right roll, as AOA increased through 5 degrees. During the recovery, they appeared to try to keep the recovery rate within the range that they had roll authority, and ran out of air. The certification requirement is to ensure that the control of the aircraft remains normal sense after the stall, but the icing went beyond the expected conditions to be encountered. At a low speed stall with manual, reversible controls the dynamic load is not normally going to be a nuisance. At higher speeds, the force can become problematic. High speed stalls are self limiting, as the stall occurs the force required to enter the stall goes away, but a few tails that have been torn up indicate if you try really really hard you can hold into buffet for long enough to break things.




Re the Saab, I'll PM you a dropbox link... have the report somewhere around. Take home is some of the stuff around the plane has good reasons to be there.
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Old 23rd Jan 2023, 10:02
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Originally Posted by fdr
Good point. Roselawn was a hinge moment reversal that gave aileron snatch. The Indon event, it isn't noted in the report but is in the dataset, and shows a point were the wing became distorted from the aileron moment, and the aircraft rolled in the opposite direction. At that point it was still in one piece, not long after it wasn't.

The hinge moment is AOA dependent, and the ATR didn't much like the AOA that it was forced to. The pressure distribution on the wing in general from runback doesn't help at all, and does impact the effectiveness of the TE down aileron. The moment change however drove the aileron to command a right roll, as AOA increased through 5 degrees. During the recovery, they appeared to try to keep the recovery rate within the range that they had roll authority, and ran out of air. The certification requirement is to ensure that the control of the aircraft remains normal sense after the stall, but the icing went beyond the expected conditions to be encountered. At a low speed stall with manual, reversible controls the dynamic load is not normally going to be a nuisance. At higher speeds, the force can become problematic. High speed stalls are self limiting, as the stall occurs the force required to enter the stall goes away, but a few tails that have been torn up indicate if you try really really hard you can hold into buffet for long enough to break things.

Re the Saab, I'll PM you a dropbox link... have the report somewhere around. Take home is some of the stuff around the plane has good reasons to be there.
The only vice i can think of with the SAAB was the tail stall possibility on the A model. It was fixed on the A by locking out flap 35. The B model which are by far the majority have a completely different horizontal stab, larger and no stall issue. Some A models also have a slightly different main wing, the fairchild wing.

WRT the ATR, my fault using the wrong terminology, it was a hinge moment. The airflow over the wing at specific AoA would force the aileron to move with significant force. This would lead to a strong uncommanded roll until AoA was reduced. It was not stall related, and happened at high speed as well. The DGAC got into strife because they had known about the hinge moment since certification, however rollover events in service had continually be called pilot error, until Roselawn...

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Old 23rd Jan 2023, 12:45
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Originally Posted by 43Inches

WRT the ATR,...
....however rollover events in service had continually be called pilot error, until Roselawn...
Icing can't be completely ruled out until the thrust and energy state of the aircraft can be reconciled. It appears unlikely. the roll appears to be a departure post stall. There is a suggestion of a slight pitch up prior to the wing drop. The CVR and DFDR will hopefully give answers as to the reason for the low energy state of the plane.

The video from the cabin, if it was faked, they went to extraordinary lengths. I don't believe that is likely, I fear that is the final moments of unfortunate pax and crew. The spectra of the audio comes out as below, the cell phone ?owner?'s voice is clearly traced, There is a line at 1760-1780Hz that would be interesting to pin down, it has a slight frequency drift, and I doubt that it is blower related, it isn't a simple harmonic of 50Hz or 400Hz. Would be interested in what gives that on an ATR72. If someone has the normal RPM range of the prop, that would be worthwhile. The engines are apparently winding down post accident, the spectra is clear on that, and those are more than likely to be the turbine running down. It isn't that often that a signature of an engine comes up after impact. The prop would have a reinforced 6th harmonic of the shaft rate, which is probably around what... 1100RPM, less than 20Hz shaft, 120Hz blade rate. Harmonics above that would then be at 12th, 18th.. and they don't seem to fit the wind down line, so that is going to be from the turbine. This would be likely classified as unsurvivable due to the attitude at impact, but the video/audio will give some insight into what can and what cannot be done to improve cabin safety. For flight crew, wings level at impact is an imperative, if possible by any means. This audio hints to that. I doubt that meaningful safety enhancement can be made to the cabin survivability for this type of event, but this video should be central to some serious consideration by the adults, if any remain in the building.










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Old 23rd Jan 2023, 13:42
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Probable Visual Approach In VMC

hans66; How does this compare with any relevant published procedures?

The video shows the weather to be sunny VMC, so it's conceivable that the crew could have requested and flown a visual approach with a left base leg over the old airport.
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Old 23rd Jan 2023, 14:04
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Re the Saab, I'll PM you a dropbox link
Any chance too thanks fdr?
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Old 23rd Jan 2023, 16:00
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Originally Posted by GlueBall
hans66; How does this compare with any relevant published procedures?

The video shows the weather to be sunny VMC, so it's conceivable that the crew could have requested and flown a visual approach with a left base leg over the old airport.
They were VFR, so visual approaches only . All domestic Flights in Nepal are VFR.
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Old 24th Jan 2023, 08:14
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Originally Posted by GlueBall
hans66; How does this compare with any relevant published procedures?


The video shows the weather to be sunny VMC, so it's conceivable that the crew could have requested and flown a visual approach with a left base leg over the old airport.

There are no publisshed procedures for the runway 12 , there are for runway 30 . The flight radar below shows the path of a known runway 12 landing . The fateful flight was doing similar approach on the other side .


Originally Posted by Seat4A










Originally Posted by ATC Watcher
They were VFR, so visual approaches only . All domestic Flights in Nepal are VFR.
This New Airport will be equipped with ILS .But will only be operational next month . They made the airbus land with VFR to open the airport .


India has blocked the installation of ILS system due to some overlap at the other new International Airport , GBIA Gautam Buddha International Airport . Flights are currently closed due to consistent bad visibility for jets .
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Old 24th Jan 2023, 10:02
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"India has blocked the installation of ILS system due to some overlap at the other new International Airport , GBIA Gautam Buddha International Airport . Flights are currently closed due to consistent bad visibility for jets ."

Dont understand that, the 2 airports are about 95K apart, they should not interfer with each other.
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Old 24th Jan 2023, 10:10
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Originally Posted by michaelbinary
"India has blocked the installation of ILS system due to some overlap at the other new International Airport , GBIA Gautam Buddha International Airport . Flights are currently closed due to consistent bad visibility for jets ."

Dont understand that, the 2 airports are about 95K apart, they should not interfer with each other.
Kushinagar Airport across it was also recently opened . Indian Shenanigans basically . One of the Approach apparently enters Indian airspace .
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Old 25th Jan 2023, 12:27
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Electric Blower

Hi FDR, you mentioned that the 1770 hz is not a multiple of a 400 hz supply. If the blower motor is an induction motor then it will have a slip percentage. if this is 12% then that gives a possibility of 2000 hz, which is the 5th harmonic.
Could you calculate the engine spooling down speed from the descending pitch tone..? It must have something to do with the number of blades on the rotors.
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Old 25th Jan 2023, 15:00
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Originally Posted by scifi
Hi FDR, you mentioned that the 1770 hz is not a multiple of a 400 hz supply. If the blower motor is an induction motor then it will have a slip percentage. if this is 12% then that gives a possibility of 2000 hz, which is the 5th harmonic.
Could you calculate the engine spooling down speed from the descending pitch tone..? It must have something to do with the number of blades on the rotors.
Normally the spectra will relate to the fan or to the shaft.. On one accident, it was possible to determine the acceleration/deceleration of the engine from the momentary overspeed/underspeed of the CSD, as it maintained control, those happened to be tied to the f of the cockpit ventilation system fans, that was the shaft, never caught higher harmonics. .. Your thoughts on the slip is an interesting point, the design would be worth some research. I am not particularly familiar with the ATR, but assume that the system is a DC gen, as a starter generator, so the fans would probably be decoupled from any variations in a drive to the gen itself. That is a WAG, based on similar designs.
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Old 25th Jan 2023, 15:13
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Both recorders are being sent to Singapore tomorrow for readout and analysis.
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Old 26th Jan 2023, 06:59
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Originally Posted by grizzled
Both recorders are being sent to Singapore tomorrow for readout and analysis.
Only 11 days….. and counting. You'd never want to rush these things.
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Old 26th Jan 2023, 09:53
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Originally Posted by pilotmike
Only 11 days….. and counting. You'd never want to rush these things.
That is right. This a bit longer process would indicate they are careful not to make mistakes and are tying to get a neutral independant report. Good on them . I know many other Sates much more advanced that Nepal which would have already leaked things to the media and deliver "culprits" to cover their backside.
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Old 26th Jan 2023, 12:12
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Originally Posted by ATC Watcher
That is right. This a bit longer process would indicate they are careful not to make mistakes and are tying to get a neutral independant report. Good on them . I know many other Sates much more advanced that Nepal which would have already leaked things to the media and deliver "culprits" to cover their backside.
You might care to note that my comment was not about the wise decision to send the recorders off to a competent Authority to have them read; on that, I'm pleased to see we are both in full agreement.

Rather it was about the reported time taken to send them.
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Old 26th Jan 2023, 13:56
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Originally Posted by pilotmike
....it was about the reported time taken to send them.
yes I got this too, and while I can understand your frustration , this is Nepal and 11 days is not really unusual.to get things done right in there .. CAAN ( the Nepalese Civil Aviation authority) has considerably improved over the last years, and is well above average compared to other poorer countries in economic difficulies such as Nepal Large airlines such as Buddha or Yeti are far more powerful than some CAAN employees and I am glad to see that they managed to keep their independance here . It took 11 days , but they managed.

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Old 27th Jan 2023, 00:23
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Originally Posted by ATC Watcher
CAAN ( the Nepalese Civil Aviation authority) has considerably improved over the last years, and is well above average compared to other poorer countries
Hi ATC W. I agree with most of what you have said re this accident, and you are right that CAAN made some excellent progress in the past few years – until recently. Sadly, since his appointment (about 11 months ago) the new Director General has set aviation safety (and efficiency, and compliance) back years. It’s incredibly frustrating because CAAN has many dedicated knowledgeable professionals who are now cowering at their desks as this dictator wreaks havoc. I could list many examples but that’s likely better via PM, so feel free.

Regarding the recorders, and the accident investigation, CAAN is not involved at all; it is not represented on the investigative panel and does not have observer status. So far the panel is undertaking their job seriously and diligently, hence no leaks.

Lastly, anyone interested in possible background factors (NOT root cause) related to this accident would find the latest Nepal AIP Amendment (#2 – 2023), and Amendment 9 of 2022, to be of interest. In a nutshell, there was great pressure to open Pokhara on January 1st, even if things that should have been in place were not.

In any case, it’s a damn sad accident.

Last edited by grizzled; 27th Jan 2023 at 01:20.
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Old 27th Jan 2023, 07:49
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Hi Grizzled.
I was not aware and sad to hear that their new DG was that bad., but as I said before I have no recent experience there and did not follow closely the set up of the 2 new airports which must have been paid by someone else no ? Thanks for the link to the amemndements , the 2023 one is very relevant , especially the empty part about the flight procedures ..
I will PM you Thanks . , .
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Old 27th Jan 2023, 08:56
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regardless whether procedures were in place or not, the weather on the day looked fine and any professional pilot should be able to execute a visual approach to an airport in those conditions and land safely (assuming no other factors). Also considering most airports in Nepal are VFR they should be well practised in this type of flying.
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