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Nepal Plane Crash

Old 29th Jan 2023, 01:33
  #401 (permalink)  
 
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Originally Posted by michaelbinary
Unfortunately, reality in this case doesnt agree with you does it,
The fact that an out of control aircraft passed thorough a 45 degree bank angle does not imply that an aircraft cannot be in control at a 45 degree bank angle. There is no conflict between the reality of this case and anything I stated.




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Old 29th Jan 2023, 02:23
  #402 (permalink)  
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Originally Posted by Stevedd32
As a retired private pilot I am amazed having read pretty much all of this thread but found no reference to what is to me the most likely cause of this crash. Hundreds of single engine pilots over the years have died attempting to do a circuit to land after an EFATO. However many thousands of hours they might have, some are obviously not aware of the fact that IF YOU ATTEMPT A STEEP TURN WHEN FLYING LOW AND SLOW YOU ARE DEAD MEAT!
They assume (presumably due to lack of training) that they only need to apply opposite aileron to level the wings! This is intuitive but fatal. They do not realise that in this situation the drag caused by opposite aileron merely stalls the inside wing promoting a spin.
Google Fairchild B52 crash for a perfect example. You can see the pilot applying opposite aileron (spoilers) as the plane, at 90deg bank spins into the ground.
The key question with regard to the Yeti disaster is, did either the PF or the captain have recent training on incipient spins? Either on a simulator or an aircraft?
All of this assuming of course that there was no defect on the aircraft.
The B52 is another matter entirely. models prior to the G has tiny "feelerons...." Roll control is by spoiler, and given the design of the wing that should be obvious as to why. You will note a similar issue with the braced wing greenie plane that Boeing has been recently funded by NASA to look at (again.... again... again). The Fairchild AFB bingle shows the fundamental problem of having a design that was not expected to be doing aerobatics being flown by a clown looking for a big top and an audience. The Buff has a very small chord rudder, and placing a highly swept wing into an unloaded high bank angle is going to get entertaining promptly. The plane will rapidly get an uncommanded increasing bank angle due to yaw and that exceeds the control authority. The only things they had left were asymmetric thrust and increasing g load to increase the roll moment of the spoiler, along with max top rudder. The ego exceeded competency well before sign on for that mission, and at least one good guy died trying to mitigate the risk of a command structure that was disinterested in managing risk. Had they bothered to pass their intended dynamics past anyone with a passing competency in aerodynamics, perhaps they might of not had the photo op.

steep turns by themselves are just another free force diagram solution.... but stupidity and ignorance at low altitude has consequences.

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Old 29th Jan 2023, 03:15
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I expect the turning condition inside a thermal is much different than free-air conditions due to a significant variation in vertical windspeed/updraft from the center to the outside, leading a tight turning plane to experience a much higher AoA on the wing towards the center than the wing to the outside.
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Old 29th Jan 2023, 05:32
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Derek Piggott wrote that a glider could not be stalled from a 45° bank because the elevator did not have enough power to reach stalling AoA in the curving airflow. But then there's aerobatic gliders such as the Puchacz with lots of elevator that can be spun from a 45° bank as I determined at a safe altitude.

Powered aircraft are a different case because thrust moment generally induces a pitch up and there's also slipstream. Much depends on the geometry of thrust lines and tail placement.

Recovery from a low level spin entry is often not possible before the ground gets in the way. Prompt recognition of decaying airspeed and recovery are key.

The crew may have missed a decaying airspeed situation, perhaps because of wind gradient, as well as inadequate power for the configuration.

Heavy windshear downwind of terrain including buildings can upset the applecart.

The video does not show the nose going down until the wing drop.

I can testify that there is a moment of WTF is happening when it unexpectedly goes pear shaped. Prompt stick forward just worked for me that day.

Once the FDR is available, the investigators will likely replicate the situation in a sim to determine the point where recovery was no longer possible, and also see how other crews manage. There have been many cases where the "survival" rate of other crews was low.
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Old 29th Jan 2023, 13:22
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Prompt stick forward just worked for me that day.
Exactly, it's a matter of training and experience. I fly a Pawnee towplane whose stall warner goes off earlier than is necessary. I frequently get some beeps when in a gliding base-to-final turn. Even though I am relatively low and the ground is filling the windscreen, it's instinctive to ease the stick forward.
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Old 29th Jan 2023, 13:59
  #406 (permalink)  
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Originally Posted by michaelbinary
They were professional pilots with many thousands of hours between them, but it didnt work for them did it. I said this many posts ago, you know, 1 pilot flying 1 pilot monitoring.
So being current with the skills to fix imminent stalls etc takes it from a consious mental desision making to a subconsious reaction which is much much faster, which is why people who play top class sports drill routines1000's of times.

Having said that, once the wing dropped they were far too low for any recovery.
Keeping your airspeed is a pretty basic concept. Better learn to do that first!
But before calling for gross incompetence I should wait and see what exactly let them lose it to that point..
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Old 29th Jan 2023, 14:46
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Originally Posted by Tu.114
...which has a tendency to strike soon after takeoff, once the non-contaminated fuel has been burned up and the off-specification, water-containing or otherwise unsuitable stuff reaches the engines. Also, it would be usual in many airlines to fuel the aircraft for the round trip to a remote (-r) airport at the home base, so typically, there is a quite substantial top-up involved. If there had been something wrong, it would be noticed much earlier in flight and in all probability would have affected other flights that used the same fuel source as well.



...hitting both separate fuel systems at once? For the effects of fuel depletion in an airliner, look at Avianca at Cove Neck 1990 or Lamia more recently; this does not kill all engines at the same second.



On both engines at the same time, involving both power levers and both condition levers, i. e. 4 levers and their associated linkage and control units at once?


All those assumptions seem extremely far fetched.
Even more so when you consider fadec

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Old 29th Jan 2023, 14:54
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Originally Posted by EXDAC
The statement I responded to was made by a private rated SEL pilot. The statement I responded to was not aircraft type specific. However, I have no doubt that an ATR is quite capable of 45 degree bank turns wthout loss of control.
I particularly like the 10-15 min left on a recurrent session. This is when all the canned plans are complete, and I have crews do 45 banked turns at 120 knot without stall protection(visavis180) or the ever popular dual engine failure glide to landing. Most guys have a "what if" scenario that we do in SIM. Great learning tools.
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Old 30th Jan 2023, 09:43
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Years ago, Airbus changed the stall procedure from the old «full thrust» first, to lower the nose to break the stall, then apply thrust.
I thought this was a change in the whole industry?
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Old 30th Jan 2023, 14:37
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Flown through the centre line..?

It would be informative if we knew where the crash occurred relative to the centre-line of the runway.
Most PPLs are instructed to not exceed 15 degrees angle of bank in the climb-out, and restricting the AoB on the descent would also be wise.
Maybe what actually happened was that they were trying to align with the runway using 20 degrees AoB,.. When Ooops...they crossed the centre line, so pulled back and added more AoB to try and intercept... The rest is history.
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Old 30th Jan 2023, 15:37
  #411 (permalink)  
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Originally Posted by scifi
It would be informative if we knew where the crash occurred relative to the centre-line of the runway.
Most PPLs are instructed ....etc ...
We know exactly where the aircraft ended ( just abeam and close to the old airport) and its relation to the centre line of the other airport runway . What we do not know is the speed of the aircraft when it started to bank . As to PPL instructons well the crew here were no PPLs, had together quite some experience, so once more, before crucifying them let's wait if there is not something else in there. My gut feeling is that there is more than just overbanking on baseleg .
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Old 30th Jan 2023, 18:00
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Originally Posted by ATC Watcher
We know exactly where the aircraft ended ( just abeam and close to the old airport) and its relation to the centre line of the other airport runway . What we do not know is the speed of the aircraft when it started to bank . As to PPL instructons well the crew here were no PPLs, had together quite some experience, so once more, before crucifying them let's wait if there is not something else in there. My gut feeling is that there is more than just overbanking on baseleg .
The Preliminary Report is due out in mid-Feb. I wouldn't rule out the inclusion of FDR traces, if so they will answer most of the flightpath questions.
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Old 30th Jan 2023, 20:26
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I seem to remember an American saying. 'Watch him spin, watch him burn, he took off bank in a low speed turn'.Very appropriate to this discussion. Spectacularly demonstrated to me in a glider when I was a 16 year old A.T.C Staff Cadet on 613 at R.A.F. Halton!.
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Old 31st Jan 2023, 17:08
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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.


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Old 31st Jan 2023, 21:22
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“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.”


Tbh that speaks volumes. I’d believe they don’t have the volume of pilots for the volume of operations. Very notably the airlines tend to put on extra flights according to the volume of pax turning up at airports seeking flights last minute. I got a place on a Buddha ATR72 out of Pokhara, but when I was in the queue for boarding a selection of passengers were pointed to a Buddha Beechcraft King Air 200 which was put on last minute to fulfil extra unexpected demand. I imagine pilots are often asked to do overtime and glad of the extra cash.
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Old 31st Jan 2023, 23:07
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Hi ATC Watcher, sorry for the slow reply, but I have been busy recently. You said.. ''As to PPL instructons well the crew here were no PPLs,''
This is not true.. All pilots either military or commercial start off with the PPL syllabus, and one of the first recommendations is to limit the AoB whilst in the circuit.
As for the position of the crash, I have only been able to find one reference to this, and it puts the location just a few yards short of the centre-line.
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Old 1st Feb 2023, 05:40
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Originally Posted by scifi
Hi ATC Watcher, sorry for the slow reply, but I have been busy recently. You said.. ''As to PPL instructons well the crew here were no PPLs,''
This is not true.. All pilots either military or commercial start off with the PPL syllabus, and one of the first recommendations is to limit the AoB whilst in the circuit.
As for the position of the crash, I have only been able to find one reference to this, and it puts the location just a few yards short of the centre-line.
PPL or CPL is not an issue. Pilots flying passengers are expected to know visual circuit procedures. Upto 30° bank can be used even in jet like A320. In a circle to land you should be on approach path vertically and laterally before 300ft. From then on nothing more than 5°to 7° to maintain the RW centre line.
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Old 1st Feb 2023, 07:16
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@scifi : I hear what you say , true of course, but I was trying to say is that they were no newbees , both were ATPLs with thousands of hours and landed visual a ATR72 multiple times before , also recently at this new airport , since Yeti ATRs are mainly doing this route. So unlikely to make basic mistakes. As Vilas said . banking 30 degrees is not an issue in any type if you aircraft is properly configured at the right speed.

Now the verry insteresting recommendations posted by grizzled are very interesting , if they are all refering to the Yeti Crash, , I am not sure as they mix STOL and Heavy airraft Ops . But if hey are, they would point at 2 other issues : fatigue and maintenance. . That, if indeed they are based on the Yeti preliminary investigation , would explain a lot more . But these are only leaked recomendations .. Waiting for the real preliminary to extrapolate further.
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Old 1st Feb 2023, 08:17
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FDR and CVR are in Singapore and No Means to open it here .Remember There is EU Air Safety Black List to overcome . The Review was postponed . Hence , Just to make things extra safe , these could be the recommendations by people , experts in the Body. The Crash Video's availability might have been the cause to suggest the changes for Stabilization Altitude. Recommendations Concerning Minimum Visibility were applied even before the Tara Air Crash , now Flights to lukla for example don't happen with a guaranteed visibility window .

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Old 1st Feb 2023, 09:31
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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.

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

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