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TransAsia in the water?

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TransAsia in the water?

Old 5th Feb 2015, 08:52
  #161 (permalink)  
 
Join Date: Mar 2011
Location: Around
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To an ATR 72-600 pilot...

Does the 600 have an auto trim on the rudder and, if so, would it cope with an engine failure and remain engaged?
Yes new addition on the 600, only available once the YD is engaged.
BO0M is offline  
Old 5th Feb 2015, 09:05
  #162 (permalink)  
 
Join Date: Feb 2015
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Yes that definitely looks feathered to me.
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Old 5th Feb 2015, 09:08
  #163 (permalink)  
 
Join Date: Nov 2005
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if you engage yd. AFTER engine flame out...autotrim is not operative
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Old 5th Feb 2015, 09:47
  #164 (permalink)  
 
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Big time speculation here...

With the retrieval of the black boxes we should know soon enough what happened. It will be interesting to see if the stall warning was activated but for the time being I'll just ask questions to the pilots that fly the 600 and to those who know the airport of departure.

First… To those who know this airport. Do we know if one of the SIDs at this airport requires a right turn after departure?

Flight tracking shows a right turn followed by a left turn and then back to the right where the aircraft is almost on runway ending but off its centre axis. To me this seems they were struggling to control the aircraft.

Second… To ATR 600 pilots. What is the Vmca of this aircraft? What is the Stalling speed of this aircraft assuming a normal fuel load and pax load (58 + crew) to make this flight to destination? Assuming we can come close to its GTOW figures, we can probably figure out the takeoff speeds, a clean stall speed and one with flaps at takeoff position.

Weather was basically VFR with some rain and IIRC the winds on the ground were 10-15kts.

Now for the speculation part…

We know from the flight tracker that the aircraft reached about 1300 feet. The highest speed attained was 116kts, the lowest was 81kts and in its final stage prior to impact was increasing slightly to show a recorded speed of 85kts.

Now these speed are most likely ground speeds so if we take a 10kts headwind component we can assume the IAS would have been 126kts, 91kts and 95kts. Now assuming those IAS speeds are correct are we close to a stalling speed for flap 0 or flap in takeoff position for an ATR 600 for a given weight at takeoff?

We know one of the pilots called the “mayday and engine flame out” so we can almost ascertain there was an engine failure and most likely the left one. Why the left one? Because of the pictures showing us it was feathered or almost feathered, but definitely had a different pitch angle on its blades versus the right engine’s blades and finally it was turning slower than the right engine.

I think there is the possibility that the left hard over was a Vmca departure, a stall or a combination of both. From the video we see the aircraft seems to be level and descending then the left roll occurs.

Was this just a stall or a Vmca departure?

Perhaps has they were “gliding” towards the open area beyond the elevated highway, the pilots knew they were not going to clear it and added power to the one engine producing power, the right engine (on the pictures we see this because the prop is rotating faster).

At that moment perhaps they were close to Vmca and as the power came up there was not enough authority on the controls to keep it level and the aircraft rolled left.

This is just an exercise and is all speculative on my part… I’m not blaming anyone or pointing the figure at anyone, it is merely here for discussion purposes…

Now for your thoughts and view point and please keep it civilized!




In regards to the left hand engine and its propeller, if indeed this pictures shows that left engine it seems to me to be in a feathered position.


Last edited by Jet Jockey A4; 5th Feb 2015 at 13:49.
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Old 5th Feb 2015, 10:01
  #165 (permalink)  
 
Join Date: Sep 2010
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Adding power doesn't increase Np.
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Old 5th Feb 2015, 10:05
  #166 (permalink)  
 
Join Date: Oct 1999
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What's the difference between a VMCA departure and a spin entry?

For a spin, we increase AoA to the stall, and induce a yaw input using rudder (deliberate, or unintended through mishandling of the rudder), the inner wing lets go and drops, followed by the nose, and you're spinning. I know this having done it deliberately literally hundreds of times.

I'm not a multi-engine pilot so VMCA is theory to me. However, as I understand it the mechanism is similar to that of spin entry, except the yaw is induced by assymetric power overcoming the ability of the rudder to compensate, due low airspeed. Also, a VMCA departure can presumably happen when both wings are (before the event) below stall AoA. But the outcome is the same - inner wing stalled, un-commanded wing drop, and you're spinning.
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Old 5th Feb 2015, 10:10
  #167 (permalink)  
 
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the inner wing doesn't stall.

You run out of rudder the aircraft continues to yaw. The wing starts lifting you hit full cross controls and it continues to yaw into the failed engine and the wing keeps going up. All happens in a matter of seconds.

Only way you can get out of it is by chopping the power on the good engine.
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Old 5th Feb 2015, 10:13
  #168 (permalink)  
 
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Thanks Mad Jock. Didn't realise the inner wing didn't stall in the latter stages of a VMCA incident.
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Old 5th Feb 2015, 10:15
  #169 (permalink)  
 
Join Date: Oct 2013
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It is always worth trying to remember that the occupants of an aircraft, have a 90% chance of survival if you contact the ground UNDER CONTROL. Fly the thing on!!

If the aircraft is flown in under control, the wings, elevators etc will absorb a lot of energy. It's the lack of control and vertical speed that mostly kills.

The glide stretch mindset must not be a reflex action, ever. If indeed this was the course of events in this accident, we don't know yet.

What we do know from photographic evidence the aircraft was not under control.
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Old 5th Feb 2015, 10:18
  #170 (permalink)  
 
Join Date: Jul 2014
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More info on "speeds"

Hope this helps to better understand the various speeds: http://www.skybrary.aero/bookshelf/books/493.pdf
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Old 5th Feb 2015, 10:35
  #171 (permalink)  
 
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It may stall depending the reason why you are hitting Vmca

But it certainly doesn't have to stall. Its the yaw which causes the roll not loosing lift.
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Old 5th Feb 2015, 10:52
  #172 (permalink)  
 
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Originally Posted by freespeed2 View Post
If the pilot concentrates on maintaining altitude during the exercise then at Vmca the aircraft will roll very rapidly to the failed engine.

Vmca is generally close to the stall speed. Maintaining aft control column and max rudder deflection at this speed has a name: Full pro-spin action.
And the rapid roll is a typical 'auto-rotation' entry to a spin.
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Old 5th Feb 2015, 11:15
  #173 (permalink)  
 
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Given the evidence from the flight tracking (which has to be taken with a pinch of salt but is the best we have until the FDR is decoded), it looks like they had engine and/or propeller problems somewhere around AA.

Whatever happened and how it was handled left them with significantly less airspeed than before, probably well behind the drag curve for SE flight. The RoD appears to be c. 1,000fpm at that stage.

In the final moments, the airframe got so slow that it departed, looking like a mix of Vmca effects and a stall/spin. The still frames from the video, as others have pointed out, show what looks like substantial/full up elevator deflection (the “gap” in the stabiliser), which ties in with a stall/spin.

As to what actually happened to start this chain of events, there are many failure modes for a turboprop power plant, some much nastier than others...
FullWings is offline  
Old 5th Feb 2015, 11:20
  #174 (permalink)  
 
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I don't normally comment on these threads as I don't fly TP's however aerodynamics are aerodynamics regardless of the type and something strikes me looking at the speed / time / alt plot.

From the point just after rotation at about 100' the speed starts to decay, however the ROC remains surprisingly steady until they pass approx. 1100' when the ROC is reduced slightly. By this point speed is now passing below 100kts and then drops suddenly with associated loss in altitude of around 500' which looks like a stall and attempted recovery. The speed however never gets back above 100kts from this point and altitude continues to reduce steadily until the point of impact.

It looks to me that the speed was allowed to decline with constant ROC until the point of stall following which insufficient speed was attained during the recovery and the aircraft remained on the back of the drag curve unable to accelerate or climb on one engine.

Looking at the final video clip the aircraft is descending with significant positive AoA and I suspect the poor crew, out of options, attempted one last pull to avoid hitting the building resulting in a wing drop.
As it happens this might have been the one thing that saved lives Vs actually hitting the building.
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Old 5th Feb 2015, 11:32
  #175 (permalink)  
 
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"On Feb 5th 2015 the airline reported that the two pilots at the controls had 4,914 hours and 6,922 hours total flying experience, an instructor with 16,121 hours total occupied the observer's seat. The crew had signed the flight papers, that showed no unusual circumstances"

The instructor wouldn't pull an engine on a Line Check would he?
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Old 5th Feb 2015, 11:38
  #176 (permalink)  
 
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@ offa...

The instructor wouldn't pull an engine on a Line Check would he?
I certainly hope not. That would go I'm sure against any decent airline's policies.

If he did that would be seen as criminal I'm sure with dire consequences for all involved.
Jet Jockey A4 is offline  
Old 5th Feb 2015, 11:38
  #177 (permalink)  
 
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The line check is supposed to be an observation of a normal operation to ensure that all SOPs are adhered to.
Nothing more.
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Old 5th Feb 2015, 11:42
  #178 (permalink)  
 
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Perhaps he was there to help observe what the pilots had reported with a problem on the left engine.

With 3 pilots in the cockpit it will be interesting to see how or if any crew coordination occurred.
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Old 5th Feb 2015, 12:15
  #179 (permalink)  
 
Join Date: Feb 2008
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Looking at the footage of the luggage being retrieved from the tail section in the river, it appears there are a large number of extremely heavy suitcases being removed. I know they will be full of water but still ...
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Old 5th Feb 2015, 12:37
  #180 (permalink)  
 
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From the point just after rotation at about 100' the speed starts to decay, however the ROC remains surprisingly steady until they pass approx. 1100' when the ROC is reduced slightly.
If the “speed” in question is groundspeed (which I think is what is reported), then that would be normal for a takeoff into-wind as you climb at constant IAS into an increasing headwind. The ROC reduction is normal at flap retraction height.
By this point speed is now passing below 100kts and then drops suddenly with associated loss in altitude of around 500' which looks like a stall and attempted recovery. The speed however never gets back above 100kts from this point and altitude continues to reduce steadily until the point of impact.
Yes, it’s all going wrong now. Only one thing is certain and that is that drag is more than thrust so the flight path is now angled downwards. Why there is that imbalance remains to be seen. Could be a) high induced and trim drag from slow (IAS) flight, b) drag from an unsecured power unit, c) lack of power from the good(?) engine, etc. Or a combination of all of them...
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