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TransAsia in the water?

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TransAsia in the water?

Old 8th Feb 2015, 14:57
  #501 (permalink)  
 
Join Date: Feb 2002
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Quote:
Originally Posted by AAKEE
Bottom of the drag curve, lovest foot per minute descent.
On the high speed side of the drag curve, where a straight line from origo(at zero winds) meets the drag curve, you would find the speed for best glide i guess ?
No, you seem to be confusing the drag curve with the power curve.

Maximum range is at the bottom of the drag curve, but on the power curve it's where it meets the tangent from the origin.
But doesn't that only apply in cruising flight? When lift equals weight, then best L/D is at minimum drag, by definition. But it was my understanding that in a glide, the lift vector will be greater than weight, and will vary with speed such that best glide will be at a higher speed (more lift) than max range speed (minimum drag) or the even slower max endurance speed (minimum power).

I know it's a bit pedantic, and probably off topic, but I had it straight in my mind until now...
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Old 8th Feb 2015, 14:58
  #502 (permalink)  
 
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Toruk Macto

Could a certain engine part fail and give indications that eng is still producing some power when in fact it's not ? Or eng surge give ind that eng may have failed but actually still operating ?
Simple answer = yes

That's why we need analysis of the CVR and DFDR beyond what this discussion board is working with.
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Old 8th Feb 2015, 14:59
  #503 (permalink)  
 
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Originally Posted by Shaggy Sheep Driver View Post
Thanks for the clarifications, guys.

Wasn't the call "engine flame out" simply reporting the fault indication that lit up on the flight deck, rather than a confirmation that any engine had in fact flamed out?
I don't think so. The Mayday call was at 10:53:34

On Feb 6th 2015 Taiwan's ASC reported that the investigation so far determined from flight data and cockpit voice recorders:

the aircraft received takeoff clearance at 10:51L, in the initial climb the aircraft was handed off to departure at 10:52:33L.

At 10:52:38L at about 1200 feet MSL, 37 seconds after becoming airborne, a master warning activated related to the failure of the right hand engine

At 10:52:43L the left hand engine (engine #1) was throttled back and at 10:53:00L the crew began to discuss engine #1 had stalled.

At 10:53:06L the right hand engine (engine #2) auto-feathered. (This is incorrect. #2 auto-feathered at 10:52:38) (Maybe they meant #1 auto-feathered at 10:53:06)

At 10:53:12L a first stall warning occured and ceased at 10:53:18L.

At 10:53:19L the crew discussed that engine #1 had already feathered, the fuel supply had already been cut to the engine and decided to attempt a restart of engine #1.

Two seconds later another stall warning activated. At 10:53:34L the crew radioed "Mayday! Mayday! Engine flame out!", multiple attempts to restart the engines followed to no avail.

At 10:54:34L a second master warning activated, 0.4 seconds later both recorders stopped recording.
Later the day Feb 6th 2015 the ASC also released an English version of the initial release detailing further that when the first master warning activated associated with the right hand engine the crew "called it out", then the left hand engine thrust lever was progressively retarded to flight idle.

At 10:53:24L the condition lever was set to fuel shut off position resulting in the shut down of the left hand engine. Following several call outs to restart the left hand engine the parameters suggest the left hand engine was restarted at 10:54:20L, however, at 10:54:34L another master warning sounded, the CVR recorded unidentified sounds and both recorders stopped.

Last edited by Lost in Saigon; 8th Feb 2015 at 17:05.
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Old 8th Feb 2015, 15:02
  #504 (permalink)  
 
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Originally Posted by TheInquisitor View Post
...
plenty of evidence to suggest they may not have been stalled. That they were close to the stall appears to be in no doubt.
I sincerely hope you are not a Pilot. If so, please let me know which Airline so I can avoid it.

Even if you are in a glide it is not a good idea to fly close to stall Speed, no matter what the circumstance. This only reduces your vital margins (against stall or loss of directional control) and Options (by significantly deteriorating L/D and thus glide distance).

Stall is at Cl max. Best L/D is at waaayyy lower Angle of attack than this. Hadn't they flown so slowly they might have been able to pass the Bridge without stalling and losing the left wing. This would have increased chances of survival even after the fatal mistake of shutting down the wrong engine (which - admittedly- isn't a first in aviation).
In so far People who insist on: Keep airspeed, don't rush things are absolutely right. This case here is about as good an example for this as it gets.
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Old 8th Feb 2015, 15:52
  #505 (permalink)  
 
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Too little information at this time.

There is a lot of important information missing from the plot as well.
Autofeather on the ATR used to be linked to the thrust selection knob whose position is not reported. Moving to climb would cancel uptrim and autofeather. Depending on what profile they flew this might have already been the case.

Did a few hours on type ATR 72-200's and it should be controllable with a non-feathering prop at any speed above Vmca. Be quick but you should have the "one" second to react and make sure you got it right. I can confirm the torque increase when going to feather making a bit of a yaw to the good side before telling you clearly which one has failed. Just keep your nose straight.

We'll have to see what the DVDR and CVR analysis together with the data that can be recovered from the ECU's and maintenance computer will show once examined.

IMHO the funny things in the data plot released are:

Why did they move the PL's so erratically?
Why the funny movement of the PL #1 in several steps to idle?
Why moving PLA #2 to MAX shortly before 02:53.15
The fuel flow on #1 increases shortly when #2 fails and nearly at the same time the PL #1 is reduced.
The PL #2 stays at TO and is then increased to MAX.
The rhythmic fluctuations in torque and oil pressure need an explanation.

What exactly is TQ1 and TQ2 versus Objective TQ1/2?
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Old 8th Feb 2015, 15:53
  #506 (permalink)  
 
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QRH Eng Flame Out SOP on ATR 500 series

ENG FLAME OUT (QRH 2.10)

Memo items:

1) PL (affected)......FI

2) (pre-conditionally...) If NH drops below 30% (implies no immediate relight)
CL (affected side)....FTR then FSO.

Preconditions:
* if damage suspected
Fire handle affected side pull
Single Eng Operation procedure (2.04)....Apply

*if NO damage suspected
Eng Restart in flight procedure (2.08)....Apply
If unsuccessful
Single Eng Operation Procedure (2.04)....Apply


It would be interesting to time this procedure versus the time they had..added to the confusion that ensued that led to the throttling back and shutting down of Eng #1.

There is no QRH procedure I know of for uncommanded Feathering..only for prop Over speed and Lo Pitch in flight (whichs as I poointed earlier in this forum, is a memo item

PL affected .....Idle

CL affected ...FTR..FSO


If there were Abnormal Eng Parameters there is a QRH procedure that addreses that.

It involves trouble shooting with ATPCS OFF and with adequate flight situation..
PL affected ...FI
EEC affected side ...OFF
(If successful)
One EEC fault procedure ....(2.09)apply
(If unsuccessful)
-or if TQ=0% and NP<77%
PL affected side...FI
CL affected side....FTR...FSO
Single Eng Operation Procedure.... apply

Avoid sudden PL movements.

This all looks like a handful of SOP in the time and Altitude available.

The check Airman might have suggested the PF just flies the plane at VmLB0 and focus on flight path while the other 2 crew members purely run the checklist and ATC and Cabin communication.I don't know if they would have fared any better if the power producing engine was indeed shut down.

Last edited by Trackdiamond; 8th Feb 2015 at 16:10.
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Old 8th Feb 2015, 16:23
  #507 (permalink)  
 
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ECU vs EEC and Automated Power and prop management

The. ECU (Engine control Unit) ceased since the advent of the 500 series and replaced by EEC..Electronic Engine Control...more automated in supervision and electronic engine control where the PLs were operated on scheduled gated notches..similar to A320 family and the PMS..Power Management selector in conjuction with EEC and ATPCS manages the engine power in its various flight phases and the CLs in Auto mode manages RPM.Fuel is metered automatically according to some engine control laws.So much automation could lead to pilots getting confused..as to what is it doing now?? Before control intervention..Where as conventional power controls..pilots react instinctively by adding or removing power more directly.

On this type of power Management the Pls are (for normal ops) in the notch and PMS regulates optimum power for the EEC computed ambient conditions.If more power is required for emergency contingencies the PL can be pushed futher up to the ramp..and if still in dire need for extra power..the PL can be advanced to "the wall" (no firewall as such in this type..).

To add complexity to the power management system there are the Multi Function Computers that supervise and authorise certain operation. The ATR is not your conventional steam gauge turboprop as those who have flown it will tell.
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Old 8th Feb 2015, 16:48
  #508 (permalink)  
 
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Even if you are in a glide it is not a good idea to fly close to stall Speed, no matter what the circumstance. This only reduces your vital margins (against stall or loss of directional control) and Options (by significantly deteriorating L/D and thus glide distance).
I don't think anybody here is claiming that flying close to the stall speed is a good idea - it's not the point I was trying to make, at least.

A number of posters are claiming that they were 'definitely' stalled - likely based on presumptuous analysis of video footage. My contention is that the data so far available suggests otherwise - at least for the majority of that descent. In the last seconds - almost certainly. But by then they were out of options and likely just doing what they could to avoid the worst of it (high buildings / roads / built-up area)

Loss of directional control in any ME aircraft has little to do with stall speed.

I sincerely hope you are not a Pilot. If so, please let me know which Airline so I can avoid it.
I'm guessing that you are not - at least, not multi TP.

Let's not forget, 15 people survived this - it could have been ALOT worse.
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Old 8th Feb 2015, 17:34
  #509 (permalink)  
 
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If the ATPCS was still in TO, would moving the PL to idle initiate an autofeather?
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Old 8th Feb 2015, 18:16
  #510 (permalink)  
 
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Asymmetric - A point of information

I have watched the videos of this terrible accident several times. I have nothing to add to the many technical discussions, nor do I have a publishable opinion.

There is, however, one thing I can inform you of and that is that the last few seconds of flight of the aircraft in this accident match exactly that of the last few seconds of flight of a Canberra BI 8 flying a practice asymmetric approach into RAF Wattisham in, I think, late 1969.

I was on duty in the Runway controllers caravan observing the approaching aircraft when, at about 2 1/2 miles the aircraft began to pitch up and the left wing began to drop, eventually going beyond the vertical. the aircraft then rolled to the left and after one and a bit turns impacted the ground, nose and left wing tip first. to my (then) young eyes the aircraft appeared to fold into itself and quietly exploded. Both crew were killed.

As far as I can remember the BoI concluded that the pilot had allowed the speed to deteriorate to the point that the aircraft entered the pre-stall buffet whereupon he moved both throttle levers to full. With the left engine at a low power setting to simulate failure, and the right engine at a much higher power level, the resultant asymmetric thrust caused the nose to pitch up and roll the aircraft, which stalled and spun into the ground

As stated earlier, what I saw as a 19 year old U/T airman (which has stayed with me all my flying life) and what I saw in the video of this accident were, apart from the end outcome, exactly the same. The river in Taiwan was more forgiving than the farmland in Suffolk.

The accident I witnessed was, if I remember correctly,the 23rd fatal PRACTICE asymmetric in the Canberra. I believe there were no fatalities in actual asymmetric landings.
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Old 8th Feb 2015, 19:11
  #511 (permalink)  
 
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It has been said before, but back to basics may very well prevent total disaster in flying.

I looked at an image of the cockpit of the ATR72. The airspeed is a small sort of vertical tape common to modern displays.

We all remember when the airspeed indicator was a large gauge, in the first place on a left to right scan.

Airspeed, Pitch/Bank Attitude, Altimeter

The above tells you the health of everything in the plane. Airspeed high, climbing, nose up...all is well

Airspeed low, descending, nose down? Engine dead!

Take care with the yoke and then fool around with the other fancy knobs.

NOW before some of you remind me, there are failure modes of airspeed that might fool you, but if you have proper reading instruments, the truth is easy to see.
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Old 8th Feb 2015, 19:15
  #512 (permalink)  
 
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unwanted autofeather on ATR 72 during decent.

Might TransAsia ATR72 have experienced a similar snag on #2 engine?Was there aan EEC problem or propeller Module Valve issue?

AT72 experiences unwanted propeller autofeather during descent in hrl airspace. - NASA ASRS
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Old 8th Feb 2015, 19:18
  #513 (permalink)  
 
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ACW,

The many Canberra asymmetric accidents are well documented, and you have just spurred my thoughts a little.

If you look at the endgame part of the FDR, you can see the beta on #2 reduce as soon as the #2 PL is retarded - it started to unfeather, with a still-lit engine. I wonder if this is what caused the final departure from controlled flight, and came as a complete surprise to the PF?
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Old 8th Feb 2015, 19:39
  #514 (permalink)  
 
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IIRC in the Dash-8 we practiced uncommanded feather as a lead-in to engine out procedures in the sim (had happened to someone at one point). First thing you see is extremely high torque values as the prop is trying to slow down. Procudure was power lever flight idle, condition lever start/feather then fuel off if the feather worked out okay. Been a bunch of years, so could be off in my memory (FCOM is up in the attic somewhere).
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Old 8th Feb 2015, 20:01
  #515 (permalink)  
 
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IIRC in the Dash-8 we practiced uncommanded feather as a lead-in to engine out procedures in the sim (had happened to someone at one point). First thing you see is extremely high torque values as the prop is trying to slow down. Procudure was power lever flight idle, condition lever start/feather then fuel off if the feather worked out okay. Been a bunch of years could be off in my memory (FCOM usual in the attic somewhere).
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Old 8th Feb 2015, 20:02
  #516 (permalink)  
 
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Originally Posted by TheInquisitor View Post
I don't think anybody here is claiming that flying close to the stall speed is a good idea - it's not the point I was trying to make, at least.
OK, then I probably got your Point wrong.

A number of posters are claiming that they were 'definitely' stalled - likely based on presumptuous analysis of video footage. My contention is that the data so far available suggests otherwise - at least for the majority of that descent. In the last seconds - almost certainly. But by then they were out of options and likely just doing what they could to avoid the worst of it (high buildings / roads / built-up area).
The stall is not a Black/White Thing. Separations over the wing Profile start to grow much before Cl max. This progesses up to the point where the lift starts to decrease despite increasing AoA. That is also the reason why L/D takes a significant hit way before Cl max.
I agree that they were probably not in a stall as of being beyond Alpha(Cl max). Still they were surely operating at an AoA with significant separations and rather bad L/D.

Loss of directional control in any ME aircraft has little to do with stall speed.
Not directly with stall speed but definitely with Vmca. Being slow doesn't help with this. At all.
That's my Point.
Had they succeeded in getting the second engine back online and to full power in the attitude they were in in the last 5 - 10s would only have led to them crashing in a spin in opposite direction.

I'm guessing that you are not - at least, not multi TP.
Indeed I'm not. Engineering Background.

Let's not forget, 15 people survived this - it could have been ALOT worse.
That is because they crashed into water which prevented a fire plus they lost control only in the last 2-3s.
Hadn't they lost control surely more could have survived.
This is not about crucifixation of the poor guys in the front Office who surely didn't want to die that day.
It is about stressing that even with a total engine failure keeping of airspeed and control is essential for such a heavy lump of aluminum in order to make it as survivable as possible. Getting below best glide Speed will only reduce your Options and make it even less forgiving.
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Old 8th Feb 2015, 20:23
  #517 (permalink)  
 
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If you look at the endgame part of the FDR, you can see the beta on #2 reduce as soon as the #2 PL is retarded - it started to unfeather, with a still-lit engine.
Call me thick (or not a pilot, which here amounts to the same thing), but I don't understand this. How can it be that the prop will start to unfeather when the power lever is retarded? How can the prop be feathered on a lit engine with the power lever full up? Is what you've just described not confusing, anomalous or unfathomable behaviour?
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Old 8th Feb 2015, 20:29
  #518 (permalink)  
 
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Let's not forget, 15 people survived this - it could have been ALOT worse
Sure, somebody else could have screwed up even more. There is always a room to make things even worse. Somebody else could have flown into a side of an office building...
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Old 8th Feb 2015, 20:37
  #519 (permalink)  
 
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Henra,

Hadn't they lost control surely more could have survived
I'm not so sure about that. The more I look at it, the more I'm convinced that the last few seconds of that flight were pure serendipity. They may well have been looking at a nice big fat field the other side of the river as their preferred forced landing location, when all of a sudden, the #2 fires back into life by unfeathering and flips them over. There's little to suggest (to me, at least) from their flight path that they were aiming for a river ditching as their solution - but impacting the opposite bank would perhaps have been far more likely had it not happened.

Since you were much more measured in that last post, please allow me to retract the implied ad hominem from my last response... I have to be honest, I'm a little prickly (and disappointed) at the massed hordes seemingly intent on apportioning crew blame before all facts are known...
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Old 8th Feb 2015, 21:04
  #520 (permalink)  
 
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At the height shown in videos it was too low/ too late to dive to regajn best glide speed ;all they could do was maintain existing speed in the mush with nothing left for a flare
I would also comment that freewheeling unpowered declutched prop creates very high drag, which increases if you try to speed up; been there, done that. glide slope decreasing to 2:1
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