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Nepal Plane Crash

Old 1st Feb 2023, 10:11
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When I first saw one of the ATR 72s I speculated that with that long fuselage, there would need to be a fairly careful series of checks so as not to inadvertently shift the C of G outside of the safe operating range - especially the aft limit. It would seem ever more critical with the narrow chord wing. This one seems to have had a full list of passengers so there's nothing to see there in terms of passenger loading. However in the early stages of the video, the nose high position is suggestive of an aircraft at the aft C of G limit or beyond. No-one else has made any observation along these lines, so I'm typing very softly here - it seems likely that everything was in order there as it should be. And yet, I continue to wonder if something was overlooked. The report will tell us I'm sure.
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Old 1st Feb 2023, 11:53
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The recently released Napal recommendations mention STOL several times but do not define the term. I know what STOL stands for and I fly an aircraft capable of takeoff and landing in less than 250 ft. What does STOL mean in this context?
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Old 1st Feb 2023, 12:35
  #423 (permalink)  
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What does STOL mean in this context?
I infer that in this context, "STOL" refers to an approach or departure path which is more steep, or not straight in normal terms. A slight variation on the strict interpretation of the four letters, but the steep approach to a shorter runway was an operational capability of the dehavilland Canada STOL airplanes.
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Old 2nd Feb 2023, 04:52
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Originally Posted by FullOppositeRudder
When I first saw one of the ATR 72s I speculated that with that long fuselage, there would need to be a fairly careful series of checks so as not to inadvertently shift the C of G outside of the safe operating range - especially the aft limit. It would seem ever more critical with the narrow chord wing. This one seems to have had a full list of passengers so there's nothing to see there in terms of passenger loading. However in the early stages of the video, the nose high position is suggestive of an ai rcraft at the aft C of G limit or beyond. No-one else has made any observation along these lines, so I'm typing very softly here - it seems likely that everything was in order there as it should be. And yet, I continue to wonder if something was overlooked. The report will tell us I'm sure.
A full ATR with bags will be quite nose heavy. The possibility of tail-tip does exist because boarding is thru the rear door. That is why at my airline we board the fwd zone (rows 1 to 9) first. An empty aircraft is ok to trim but the SLF will always want to sit at the rear (closer to the door) so we have to enforce seating discipline. The ATR72-500 is not particularly fussy as below image shows.



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Old 2nd Feb 2023, 07:52
  #425 (permalink)  
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Originally Posted by Pilot DAR
I infer that in this context, "STOL" refers to an approach or departure path which is more steep, or not straight in normal terms. A slight variation on the strict interpretation of the four letters, but the steep approach to a shorter runway was an operational capability of the dehavilland Canada STOL airplanes.
Indeed , to complete your answer the text below from the CAAN site gives a bit more context on how the term "STOL airport " is used in Nepal :
KTM Tribhuvan International Airport is the only international aerodrome in the country. Biratnagar, Pokhara, Gautam Buddha Airport, Bhairahawa, and Nepalgunj airports, as the busiest airports, are considered domestic hub airports. Gautam Buddha Airport at Bhairahawa is being upgraded to an international airport expected to be completed in 2022 and in Pokhara a new International airport is being build to be completed by end 2022 .. 21 Airports are short take-off and landing (STOL) airports with Aerodrome flight Information service (AFIS). a further 17 Airports are STOL airports but are not in full time operation . Airports not-in-use may be re-activated during emergencies after authorization by the Civil Aviation Authority
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Old 2nd Feb 2023, 09:48
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Originally Posted by FullOppositeRudder
However in the early stages of the video, the nose high position is suggestive of an aircraft at the aft C of G limit or beyond. No-one else has made any observation along these lines,
On what basis do you deduce that? A pitch attitude has everything to do with how the a/c is flown, ie control positions. It has little to do with C of G position. C of G position will affect what control position (and force) is required to achieve any particular attitude, and if too extreme, it risks the aircraft running out of control range to achieve all required flight attitudes - hence the limits imposed upon C of G.
Originally Posted by FullOppositeRudder
The report will tell us I'm sure.
As it is not possible to diagnose G of G position from a seeing the pitch attitude of an aircraft, as you have tried to, best wait for that report as you mention.
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Old 2nd Feb 2023, 10:10
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Fulloppositerudder's comments about C o G might be a misunderstanding, but it has made me wonder if there might have been a load shift - the bags in the forward cabin hold moving back.

Could an ATR pilot comment whether this is a possibility - I would imagine that by design the baggage could not move far enough to cause a hazard?
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Old 2nd Feb 2023, 12:18
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Last time on board an ATR72..

was flying Dublin Guernsey route. The aircraft was far from full, and the senior flight attendant asked a number of passengers to move into other seats to better distribute the weight, as she saw the aircraft would otherwise be too nose heavy.
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Old 2nd Feb 2023, 15:33
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Originally Posted by martinebrangan
was flying Dublin Guernsey route. The aircraft was far from full, and the senior flight attendant asked a number of passengers to move into other seats to better distribute the weight, as she saw the aircraft would otherwise be too nose heavy.
I was on a 737 flight to Malaga one xmas and there were only 24 passengers and we were asked to move about by the cabin crew. Not unusual.

Also there was a very famous 2003 CofG crash which killed everybody on take off, straight up and down. The plane was overweight and CoG was outside the aft envelope.
The NTSB investigator found that airlines were still using average passenger weights from 1936, but in 2003 people were on average much heavier.
This accident caused all the passenger weight tables to be updated.

https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481
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Old 2nd Feb 2023, 16:38
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Originally Posted by michaelbinary
I was on a 737 flight to Malaga one xmas and there were only 24 passengers and we were asked to move about by the cabin crew. Not unusual.

Also there was a very famous 2003 CofG crash which killed everybody on take off, straight up and down. The plane was overweight and CoG was outside the aft envelope.
The NTSB investigator found that airlines were still using average passenger weights from 1936, but in 2003 people were on average much heavier.
This accident caused all the passenger weight tables to be updated.

https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481
actually I can add an addendum to that. There is an AD on the B1900 due to the counterweight causing lockup in the pitch circuit. Due to lead melting around 700 degrees this wasn't found during the investigation. Our company had it happen, DoM looks at fdr trace, almost exactly the same but our guy plonked it on the runway. Inspection of fleet showed similar damage across all aircraft. See 2014-02-03 elevator bobweight
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Old 2nd Feb 2023, 17:03
  #431 (permalink)  
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Originally Posted by michaelbinary
I was on a 737 flight to Malaga one xmas and there were only 24 passengers and we were asked to move about by the cabin crew. Not unusual.

Also there was a very famous 2003 CofG crash which killed everybody on take off, straight up and down. The plane was overweight and CoG was outside the aft envelope.
The NTSB investigator found that airlines were still using average passenger weights from 1936, but in 2003 people were on average much heavier.
This accident caused all the passenger weight tables to be updated.

https://en.wikipedia.org/wiki/Air_Midwest_Flight_5481
Don't forget insufficient elevator travel following below par maintenance.
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Old 3rd Feb 2023, 09:00
  #432 (permalink)  
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Originally Posted by grizzled
This was published yesterday in Nepal. It's from a document the investigative team sent to the regulator. The contents seem to indicate that the panel have already gleaned some initial info from the CVR and FDR, as well as perhaps from training records, maintenance records and crew duty records. Make of it what you will. Certainly some of the recommendations are problematic for Nepal.


Originally Posted by parkfell
Item (1) & (2) Fairly standard stuff, avoiding split @rse turns onto final. Full IFR procedures with no visual approaches.

Item (3) Who will examine the TREs? A non company examiner would increase confidence. Regulator involvement.

Items (4) & (5) are very revealing. It would be interesting to know what ‘augmented’ element had been approved. What risk assessments had been carried out & the pressure applied to the regulator to approve it?

Item (5) : I assume this means the same flight crew, alternating PF & PM, for an eight sector day not exceeding 8 hour flight duty period?

Clearly tightening up, attempting to mitigate the known Threats/Errors.
The FDR/CVR will be rich in CRM training material for others to learn from this tragic accident
About 4 and 5:

The accident happens before midday local time

Flightradar shows another aircraft in the fleet regularly doing 4 flights a day, each under an hour long (18 to 54 minutes), about 17.5 hours in a week, albeit sometimes later than scheduled, which might stretch scheduled start to actual finish times, but even so doesn't seem excessive

https://www.flightradar24.com/data/a...n-amz#2ed30fdb

So perhaps as someone suggests above, the recommendations may seem more generalised rather than from specific information emerging from this event.

Edit: unless this represents changes after the recommendation (which would thus have to be at least a week old). I think I remember that the accident may have been on the third arrival at Pokhara that day. Does anyone have a Flightradar subscription that can go back more than 7 days?

Last edited by aox; 3rd Feb 2023 at 09:15.
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Old 4th Feb 2023, 07:52
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Posted by Anliv in response to my speculation:

A full ATR with bags will be quite nose heavy. The possibility of tail-tip does exist because boarding is thru the rear door. That is why at my airline we board the fwd zone (rows 1 to 9) first. An empty aircraft is ok to trim but the SLF will always want to sit at the rear (closer to the door) so we have to enforce seating discipline. The ATR72-500 is not particularly fussy as below image shows.
Thank you, I appreciate the information. I've learnt something... It's been a good day.

In response to another comment from PM:
As it is not possible to diagnose G of G position from a seeing the pitch attitude of an aircraft, as you have tried to
Yes, almost certainly the case with most (powered) aircraft because SOP dictates that it remains within certain conservative limits. From where I come from (gliding), bringing the C of G to the rear of the range can and does happen at times for operational and performance reasons. Changes in glider pitch and handling behaviour which happens when this is done is sometimes apparent to the astute observer. I was reminded of that when viewing the first seconds of the video; hence my musings - no harm intended. I do also recall several sad instances where, due either to load shift or incorrect loading of pax or cargo, things have turned out very badly. Nevertheless, thanks for your challenge Pilot Mike - point taken - we fly in different disciplines; sometimes operational considerations overlap, sometimes (most times?) they don't. I'll back out return to my afternoon nap.
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Old 4th Feb 2023, 08:09
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Faulty ASI. Over-reading.
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Old 4th Feb 2023, 08:10
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Originally Posted by FullOppositeRudder
Posted by Anliv in response to my speculation:



Thank you, I appreciate the information. I've learnt something... It's been a good day.

In response to another comment from PM:

...From where I come from (gliding), .... Nevertheless, thanks for your challenge Pilot Mike - point taken - we fly in different disciplines;
Although I an both ATPL(A) and rotary, I was also a gliding instructor, so I have a fairly reasonable appreciation of powerless flight, hopefully matching yours.

Although aft C of G is known to be slightly more efficient in conventional f/w aircraft, both powered and powerless, due to more lift coming from the tail, reducing the induced drag on the main wings, the pitch attitude is set for the performance required: a different C of G simply affects the control forces (and positions) to achieve that required attitude, to a first order of magnitude, even in gliders. I hope that makes sense and helps.
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Old 4th Feb 2023, 08:21
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Originally Posted by tfx
Faulty ASI. Over-reading.
Is this your guess made with a beer in the hand or based on serious (leaked) information ?
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Old 4th Feb 2023, 09:57
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Faulty ASI

Having at one time had a faulty ASI, I can say that they usually go faulty by under-reading. This is due to leaks in the system.
However if there are any electronics involved in the display, then all bets are off; They could read any random number.
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Old 4th Feb 2023, 12:52
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Originally Posted by ATC Watcher
Is this your guess made with a beer in the hand or based on serious (leaked) information ?
Clearly the former! IAS discrepancies will be shown on the PFDs plus the stall warning and stick pusher is triggered by the AOA vanes.
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Old 4th Feb 2023, 18:49
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More lift coming from the tail? Might be a long time ago I did aerodynamics but I think you meant less down thrust and hence less induced drag from the tailplane, the former meaning that the wings need to produce slightly less lift. Both marginally improving L/D.
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Old 4th Feb 2023, 18:57
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Originally Posted by blind pew
More lift coming from the tail? Might be a long time ago I did aerodynamics but I think you meant less down thrust and hence less induced drag from the tailplane, the former meaning that the wings need to produce slightly less lift. Both marginally improving L/D.
I mean, if the tail goes from a lot of negative lift, to just a little negative lift, so less negative lift from the tail, does that not mean "more" lift (hopefully what he meant....)? Obviously, you are correct in your reply about what aerodynamically happens, maybe just a language difference.
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