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Nepal Plane Crash

Old 20th Jan 2023, 21:42
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Originally Posted by aox
I wonder if what he says can be a bit ambiguous

It could be that he means the turn from that base leg to final is overshot or late with respect to the base leg (i.e. crossing the extended centreline), compared to others, or he might mean that others are already established on approach from a final turn a bit further out.

I'm not sure what help there is in the close ups of tracks of right hand circuits on other flights
Most witnesses to most things say things they havent actually seen and dont mention things that they have seen.
RE: the famous gorilla in the room experiment.

And unless you are a pilot most lay witnesses have no real idea what a plane is actually doing
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Old 21st Jan 2023, 01:10
  #342 (permalink)  
 
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The fact that he took video of the plane indicates it was doing something unusual.

I just read that the CVR is being analysed locally.

Last edited by agird; 21st Jan 2023 at 02:25.
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Old 21st Jan 2023, 03:23
  #343 (permalink)  
 
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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.
You run into Vmc far more often in the GA world. It's crucial in a light twin because the donks are little and a small engine doesn't produce enough power for level flight at low speeds...so you need to be really alert on takeoffs and landings.

Most commercial aircraft don't have Vmc limits because their single engines have enough power to sustain flight at any speed.

There's still Aztecs and Navajos all over the US so it's important to know. But I have no idea if the aircraft in this incident is Vmc rated or not.
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Old 21st Jan 2023, 03:40
  #344 (permalink)  
 
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The Roselawn crash was an ATR-72-212 and was aileron reversal caused by ice bridging behind the outer sections of deice boots. Found to be due to the de-ice boots being of inadequate size, the boot size was increased about halfway to what the engineers wanted to prevent future repeats. It was also found that the ATR could suffer control reversal with clean wings near the stall during early testing and this was corrected with VGs fitted in the location to adjust the airflow over the ailerons.

Tailplane icing and stalling will normally result in control pulsating and then nose down pitch. In the video there is no evidence the nose was pitching down until it rolled over, quite the opposite in that the nose seemed to increasing in pitch before it rolls over.
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Old 21st Jan 2023, 05:09
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Originally Posted by agird
The fact that he took video of the plane indicates it was doing something unusual.

I just read that the CVR is being analysed locally.
I think that even a completely normal and successful approach and landing on RWY 12 at VNPR (the new airport) could have been something worth of a video for the guy there. The airport had started operating just a couple of weeks before, RWY 12 isn't the preferential runway and even a normal approach to RWY 12 would probably bring the aircraft closer to his house (or at least they would be offering a different view) than what he had experienced with the old airport.
Personally, in this same situation, I could have taken a video as well.
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Old 21st Jan 2023, 10:10
  #346 (permalink)  

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Originally Posted by 43Inches
The Roselawn crash was an ATR-72-212 and was aileron reversal caused by ice bridging behind the outer sections of deice boots…….
The company’s ‘quick fix’ was to base the ATRs south, and deploy Saab340 north.

Not that Saab340 is invincible in icing. I recall a day flying Glasgow to Stornaway (FL160)when despite operating the boots, the IAS reduced to 160kts with MCP now selected. No ice showing on the wings No option but to descend (500fpm) to maintain speed until a significant increase in IAS occurred by FL120. On the return leg flew west of the GC track !
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Old 21st Jan 2023, 10:28
  #347 (permalink)  

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Originally Posted by Yo_You_Not_You_you
As per the videographer , the plane should have already turned by the time video starts , ie: the plane should not have been coming towards him and should be flying parallel above him . Based to previous flights he saw.
Will a stall or stall recovery take this kind of path?
Assuming the aircraft was fully serviceable, there are more than adequate indications that
you are entering / have entered the ‘incipient stage’.
A critical element being IAS monitoring. No auto throttle to give added protection.
Prima facie, there was lack of situational awareness which is often associated with high workload.
The CVR (& FDR) will be revealing.
Banking left at the point of stall, resulting in rapid roll left & significant ROD with insufficient height to recover.
All very tragic, & I would speculate wholly avoidable.

Note: GOV.UK published updated foreign travel advice today at 11.34am directing travellers to the UK Air Safety List published on the UK CAA website. Yeti Airlines is one of 21 operators listed.

Last edited by parkfell; 21st Jan 2023 at 11:11. Reason: Note: GOV.UK Nepal travel advice
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Old 21st Jan 2023, 10:39
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Originally Posted by Zionstrat2
You run into Vmc far more often in the GA world. It's crucial in a light twin because the donks are little and a small engine doesn't produce enough power for level flight at low speeds...so you need to be really alert on takeoffs and landings.
It's not so much the limited power of the donks. It is more the short lever of the tail compared to the lateral offset of the engines in the small GA twin aircraft which limits the power of rudder and vertical tail against asymmetry.
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Old 21st Jan 2023, 14:12
  #349 (permalink)  
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Originally Posted by binman054
FDR...BSAE NCSU 1985 then UAL 1988-2019...I have no idea what you're talking about sometimes but I do enjoy how you say it...
Go Wolfpack!
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Old 21st Jan 2023, 14:32
  #350 (permalink)  
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Originally Posted by parkfell
The company’s ‘quick fix’ was to base the ATRs south, and deploy Saab340 north.

Not that Saab340 is invincible in icing. I recall a day flying Glasgow to Stornaway (FL160)when despite operating the boots, the IAS reduced to 160kts with MCP now selected. No ice showing on the wings No option but to descend (500fpm) to maintain speed until a significant increase in IAS occurred by FL120. On the return leg flew west of the GC track !
When the Saab 340 came out first it didn't need any icing to get into mischief. That got sorted pretty quickly but it was entertaining.

Re Roselawn, ATR 72 etc, The event gave rise to substantial changes to §25, and added to the Appendices to the part; runback icing became a big deal, as did SCLD. (Both off those issues happen to be well modelled by FENSAP-ICE if anyone from an FAA ACO is listening... ). The rules frown on roll reversal prior to the stall however defined by the manufacturer, and for a small period below the stall reference speed. Getting reversal is usually a pretty lousy bit of design in the first place. A prop powered plane may get a pretty neat wing drop at the stall, but the ailerons should not get a reversal before the margin after the stall.

A B737 managed to get a recorded aileron reversal, happened to be about VNE+120KCAS at the time and was fixed by the wings departing the fuselage with unfortunate results. doing an inflight realignment of all AHRS platforms in a thunderstorm is part of nature selection process at work.
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Old 21st Jan 2023, 14:38
  #351 (permalink)  
 
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pilot mike

Hong Kong Runway 13 . I guess you are thinking of the the turn following the IGS approach. I am speaking of the NDB CC (no IGS/VOR then) which was a break cloud to visual. The difference of track from the NDB to runway heading was, I believe about 100 degrees, so, if visual, many people took it wide around stonecutters giving a better radius of turn but a larger turn angle. There weren't any published figures then as it was just "visual"
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Old 21st Jan 2023, 20:01
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Pokhara airport sits around 2,625 ft AMSL...it could have also played some part here regarding safe app speeds, Imho.
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Old 21st Jan 2023, 21:39
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Local familiarity

Originally Posted by JanetFlight
Pokhara airport sits around 2,625 ft AMSL...it could have also played some part here regarding safe app speeds, Imho.
Nepalese pilots are well versed in density altitude, many airports have quite high altitudes, and would surely be particularly familiar with reference airspeeds. In one of the local papers it was emphasised that this accident is an outlier to most Nepal air accidents which involve CFIT, plus mishaps relating to extreme airports like Lukla. But one never knows, and something quite “different” happened here.
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Old 22nd Jan 2023, 00:17
  #354 (permalink)  
 
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Originally Posted by martinebrangan
Nepalese pilots are well versed in density altitude, many airports have quite high altitudes, and would surely be particularly familiar with reference airspeeds. In one of the local papers it was emphasised that this accident is an outlier to most Nepal air accidents which involve CFIT, plus mishaps relating to extreme airports like Lukla. But one never knows, and something quite “different” happened here.
You are absolutely correct, hence i terminated with a simple "IMHO"...however since the very beginning when i started flying in 1994 i've always learned that in every single accident investigation we cannot exclude any single factor.
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Old 22nd Jan 2023, 05:24
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Any Idea what kind of Airflow a deep river Gorge could create ? Although the plane was not right above it but flying parallel to it in low altitude . Plus the old airport is next to it .

https://english.onlinekhabar.com/pok...ir-safety.html
EU on-site assessment has been deferred , Nepal will stay in the EU blacklist .

The major demand from EU is the split of CAAN which is both Regulator and Service provider(Airports , Ground handling ) .

Last edited by Yo_You_Not_You_you; 22nd Jan 2023 at 06:03.
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Old 22nd Jan 2023, 09:13
  #356 (permalink)  
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To be clear : regardind Yeti airlines being "banned" from the EU, as Yo-You etc. mentioned already this has very little to do with the airline itself , but it is rather the Nepalese State regulatory weakness in enforcing standard regulations to airlines and/or ATC. All the 20 airlnes of Nepal are on the list, not only a few.. To the defence of the State , it is one of very poorest countries in the world and their ability to enforce western regulations is also very poor. I was there a decade ago a few times , part of a team to try to improve things on the ATC side, We met a few times the Transport Minister at the time , he was a retired American-Nepali Architect who decided to come back and help and serve his country of birth, When we talked about radar, training staff properly to use it, licences , he replied bridges and road ifrastucture. His line of thought basically was when I have money I spend it first on Nepalese people, improving tourists safety is important but come second. I must say I cannot blame him .We managed to have a few small things accepted like changing the approach glide slope gradient in KTM from the 9 degrees to 5.3 , , but the the earthquake struck and priorities changed. There is still no ILS in KTM and will never be as the new RNP AR procedure designed by Airbus was given for free but is of no interest to the domestic airlines that operate in Nepal,

Back to Yeti, when I was there ,our local contacts had a list of who to fly with and who to avoid, Buddah was on top at that time . , Yeti was not .But I saw that Yeti and Tara ( same owner) have changed in the meantime and improved a lot . Yo-You etc can confirm or not. The current boss appears to know what he is doing , like introducing modern ATR-72s.. but the type is not suited for the Mountains destinations so they reduced airports they served.using Tara older but smaller types for those.

10 yaers ago one of the main problem for the smaller airlines was maintenance and spares. Not sure is this is still a factor today , but if it still is , it could be the elephant in the room here ..

Last remarks on the pilots. Again 10 yaers ago , all of them were local Nepali , a quite a few women too. The old Ziegler motto ( the one from Air Alpes , not Airbus) : " It is far easier to train a local mountain guy to fly than to teach an experienced pilot. to fly in the mountains " is still valid. They were good, some very good. Most of the accidents they have ,( about 1 fatal every year on average ) are weather related. There is ( at least was) no weather forecast system in Nepal , no weather stations at destination airports., just what the local Tower controller , generally alone for 8 hours) would report what he /she saw. . The environement is hostile and unforgiven .
Therefore when I read the reported experience of both the Captain and the F/O , see the weather that day and the absence of hindering terrain around , I have difficulty to believe one of them would let an aircraft stall on base leg , Must be something else. But let's see what the CVR/FDR will tell us .
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Old 22nd Jan 2023, 09:50
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Mountain weather flows;
it is very complicated and depends on time of day, solar heating or katabatic cooling and temperature inversions.
I nearly flew into the Black Forest during winter at max take off weight calculated using the ground meteorological conditions which did not reflect the air mass at 1,000ft including a 25 knot wind shear. My limited experience mountain soaring in the french alps including the wind direction reversal as solar heating in the higher mountains draws the air in along the river valleys.
I’ve flown paragliders in the lower levels of the chartreuse when the winds at the mountain tops would be fatal - local knowledge.
I’ve also quite often flown circling approaches without any previous specific training with the final approach in a valley and getting stabilised around 30 seconds before landing in a commercial airliner and 5 seconds before touch down in a tug.
Except for possible ice accretion and accepting there were no CBs in the area I would be very surprised if wx was the problem.
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Old 22nd Jan 2023, 11:47
  #358 (permalink)  
 
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Originally Posted by fdr
When the Saab 340 came out first it didn't need any icing to get into mischief. That got sorted pretty quickly but it was entertaining.

Re Roselawn, ATR 72 etc, The event gave rise to substantial changes to §25, and added to the Appendices to the part; runback icing became a big deal, as did SCLD. (Both off those issues happen to be well modelled by FENSAP-ICE if anyone from an FAA ACO is listening... ). The rules frown on roll reversal prior to the stall however defined by the manufacturer, and for a small period below the stall reference speed. Getting reversal is usually a pretty lousy bit of design in the first place. A prop powered plane may get a pretty neat wing drop at the stall, but the ailerons should not get a reversal before the margin after the stall.

A B737 managed to get a recorded aileron reversal, happened to be about VNE+120KCAS at the time and was fixed by the wings departing the fuselage with unfortunate results. doing an inflight realignment of all AHRS platforms in a thunderstorm is part of nature selection process at work.
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.
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Old 22nd Jan 2023, 12:09
  #359 (permalink)  
 
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Originally Posted by ATC Watcher
To be clear : regardind Yeti airlines being "banned" from the EU, as Yo-You etc. mentioned already this has very little to do with the airline itself , but it is rather the Nepalese State regulatory weakness in enforcing standard regulations to airlines and/or ATC. All the 20 airlnes of Nepal are on the list, not only a few.. To the defence of the State , it is one of very poorest countries in the world and their ability to enforce western regulations is also very poor. I was there a decade ago a few times , part of a team to try to improve things on the ATC side, We met a few times the Transport Minister at the time , he was a retired American-Nepali Architect who decided to come back and help and serve his country of birth, When we talked about radar, training staff properly to use it, licences , he replied bridges and road ifrastucture. His line of thought basically was when I have money I spend it first on Nepalese people, improving tourists safety is important but come second. I must say I cannot blame him .We managed to have a few small things accepted like changing the approach glide slope gradient in KTM from the 9 degrees to 5.3 , , but the the earthquake struck and priorities changed. There is still no ILS in KTM and will never be as the new RNP AR procedure designed by Airbus was given for free but is of no interest to the domestic airlines that operate in Nepal,

Back to Yeti, when I was there ,our local contacts had a list of who to fly with and who to avoid, Buddah was on top at that time . , Yeti was not .But I saw that Yeti and Tara ( same owner) have changed in the meantime and improved a lot . Yo-You etc can confirm or not. The current boss appears to know what he is doing , like introducing modern ATR-72s.. but the type is not suited for the Mountains destinations so they reduced airports they served.using Tara older but smaller types for those.

10 yaers ago one of the main problem for the smaller airlines was maintenance and spares. Not sure is this is still a factor today , but if it still is , it could be the elephant in the room here ..

Last remarks on the pilots. Again 10 yaers ago , all of them were local Nepali , a quite a few women too. The old Ziegler motto ( the one from Air Alpes , not Airbus) : " It is far easier to train a local mountain guy to fly than to teach an experienced pilot. to fly in the mountains " is still valid. They were good, some very good. Most of the accidents they have ,( about 1 fatal every year on average ) are weather related. There is ( at least was) no weather forecast system in Nepal , no weather stations at destination airports., just what the local Tower controller , generally alone for 8 hours) would report what he /she saw. . The environement is hostile and unforgiven .
Therefore when I read the reported experience of both the Captain and the F/O , see the weather that day and the absence of hindering terrain around , I have difficulty to believe one of them would let an aircraft stall on base leg , Must be something else. But let's see what the CVR/FDR will tell us .

Yeti is all ATR 72 . Having lost its Jet-stream in runway excursion and All Smaller aircraft transferred to Tara air . The Airlines also runs Himalaya Airlines Joint Venture to fly Airbus in regional routes . Yeti sadly lost its founder and MD to a Helicopter crash .
Buddha is still the top airline having expanded its fleet of ATR . Sold their 25 yr old beechkrafts

Last edited by Yo_You_Not_You_you; 23rd Jan 2023 at 10:47.
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Old 22nd Jan 2023, 16:13
  #360 (permalink)  
 
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The CVR was going to be analysed in Kathmandu.
After almost a week of the recovery, no leaks, no gossips?
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