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Turkish airliner crashes at Schiphol

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Turkish airliner crashes at Schiphol

Old 2nd Mar 2009, 19:00
  #901 (permalink)  
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Dani;
. . . you guys have no clue.
. . .
But it shows how it most probably went.
No, with respect, it is you who do not "get it" I am afraid.

"[H]ow it most probably went" is not how accident investigations conducted under ICAO Annex 13 are done. Anything else does not have the integrity of actual data and so is not worth serious conjecture.

Last edited by PJ2; 2nd Mar 2009 at 19:44.
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Old 2nd Mar 2009, 19:17
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DC-ate.....

Yes, in my opinion they has to be, but i just heard them(engine(s)) during the crash.

Old Fokker guy,
You forgot to mention that this witness/passenger hailed the pilot for his skills. And there are more.

Last observation:
The tailwing seem to broke of during first impact, it's the only big part that was aprox 100 mtr behind the a/c at the crash-site.

So now i'm not an expert and asking; suggest this that the a/c was in an angle more than a normal landing?

And why so?

Yes,the Dutch Safety Board(OVV) is informed and hold my contactinfo.

Last edited by crashresident; 2nd Mar 2009 at 19:30.
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Old 2nd Mar 2009, 19:35
  #903 (permalink)  
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brandtzag.

The same laws of physics as those involving kinetic energy?

Please, stop it now.
 
Old 2nd Mar 2009, 19:38
  #904 (permalink)  
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Lost in Saigon;
Are you aware that this engine has more than one shaft
Yes, I am fully aware of the structure of turbine engines.

...yet the high pressure compressor and turbine could continue running.
On what?
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Old 2nd Mar 2009, 19:45
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Originally Posted by PJ2
Lost in Saigon;

Yes, I am fully aware of the structure of turbine engines.

On what?
If you are aware of the structure of a turbine engine, then why do you find the condition of the low pressure fan to be so interesting?

I agree that it is highly unlikely that there would be much fuel available to the engine after it has become detached from it's pylon. But I would never support my argument based on the condition of the low pressure fan.

Last edited by Lost in Saigon; 2nd Mar 2009 at 20:04.
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Old 2nd Mar 2009, 19:52
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Steamchicken,

There are a lot of PPRuNe accident threads where partial automation is discussed as a factor - for example, autopilot on but autothrottle off, autopilot conflict between capturing glideslope and platform altitude.

Python programmers have a saying, indeed a rule-of-thumb, that "explicit is better than implicit", i.e. it's better to specify conditions tightly, provide literal information in error conditions, always be clear about what the machine is doing, what it is meant to be doing, and what actually happened.
Not sure what/who Python programmers are. From an NG rated pilot's perspective, there are some ancilliary (technologically speaking) design elements (CWS anyone?) in the flightdeck of the NG relative to peers of that generation. These elements surely handcuffed the designers from achieving ideal conditions with respect to the Python's credo above.
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Old 2nd Mar 2009, 19:54
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As a captain on the NG this seems a pretty impressive demonstration of the need to be stabilised at 1000' feet in IMC.

Being on glide and on speed does not count if the engines are not spooled up, which by accounts so far, they do not seem to have been.

If you are not stable it should be a mandatory go-around.

The exact causes of this mishap will be provided by the investigators. I hope I am wrong, but I suspect I will be adding it to my list of '737 how not to do it', alongside Adam Air, TNT East Midlands etc.

Last edited by lederhosen; 3rd Mar 2009 at 06:23.
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Old 2nd Mar 2009, 20:04
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I agree with PJ2 about the animations (nice to look at but not at all factual beyond speculation).

Some folks are still stretching too far to interpret the engines and the witnesses to suit their own pet theories. Remember that the trained on-scene investigators have already confirmed the condition and perhaps we will get a hint on Wednesday

As for the ear-witness who bravely showed up on this forum. His testimony is only as good as his first recollections and perhaps some additional recall under questioning by trained investigator/debriefers.

many of you have already poisoned any on-ward usefulness to his recall and now anything further that he may say is worthless to the investigation. His initial post id the only thing of limited value

Last edited by lomapaseo; 2nd Mar 2009 at 20:23.
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Old 2nd Mar 2009, 20:25
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Lost in Saigon;
If you are aware of the structure of a turbine engine, then why do you find the condition of the low pressure fan to be so interesting?

I agree that it is highly unlikely that there would be much fuel available to the engine after it has become detached from it's pylon. But I would never support my argument based solely on the condition of the low pressure fan.
The original notion posited by some was, the engines continued to run post-crash and the resultant high thrust levels from the departed engines was the reason they were so far ahead of the wreckage. I think that is an incorrect assessment of why the engines ended up where they are. What do you think?

My focus on the N1 was solely to observe that while there are indications of engine rotation, there are also N1 blades which are relatively straight, indicating that such rotation ceased quite quickly. My assumption that the N2 did not continue running for long and, if undamaged either by impact forces or signficant amounts dirt/mud/cowling parts etc, simply ran down, is easily supported by the lack of sufficient fuel to keep the fire lit and the turbines turning. We will know more about this of course, very shortly.

In any case, my original point was meant to address the view that the long trail of dust/smoke/steam/? was caused by a running engine and that it was so far ahead of the main wreckage because it continued to run at a thrust setting which could carry a 2400kg engine that far forward, a suggestion that has, for the reasons given, no merit or basis in fact whatsoever.

brandtzag:
Perhaps you would kindly explain "kinetic" energy an why the engines, if moving at the same speed as the airframe, suddenly appears ahead.
They are well ahead of the primary wreckage site because the initially very high vertical impact loads very likely broke both engines off the wings and they simply tumbled forward as a result of their 2.4T weight. I can't explain the "smoke/dust/vapor/?" trail because I don't know if the ground was wet, dry or ? .

The physics lesson here is straightforward I think, is it not? The 2400kg mass was travelling between 70 and 90 kts and simply continued forward until the forward momentum was absorbed by the soft ground.

lomapaseo:
As for the ear-witness who bravely showed up on this forum.
"bravely"...no kidding. For a number of reasons, I think what he has done was very risky and an unwise decision but there it is.
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Old 2nd Mar 2009, 20:25
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Captain

Captain Hasan Tahsin Arısan was one of the airline's most experienced senior pilots who had more than 15,500 hours of flying experience. Captain Arısan had been working for Turkish Airlines since 1996. He was also a former Turkish Air Force fleet commander, who had over 5,000 hours of flight time on the F-4E, the highest number of hours in the world on an F-4E
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Old 2nd Mar 2009, 20:29
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About that animation

The animation implies a stall break at some 45 degrees AoA, which IMHO can only happen if there was substantial engine thrust. Yet those few witness reports that mention engine sounds seem to place the sounds at very close to when the aircraft hit the ground. Had the engines been screaming at high power at that altitude, presumably many more witnesses would have noticed.

I have yet to see a witness report mentioning the nose pointing downwards from the horizontal at any time, as the animation implies.

Finally, the pullout close to the ground looks like a fairly high-G maneuver. Again, no witness reports that mention that kind of push-me-into-the-seat sensations.

Admittedly I haven't read the witness accounts very systematically, but my guess is that the events looked less dramatical than the animation suggests. Correct me if I've missed something. Well, anyway, we'll see soon.
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Old 2nd Mar 2009, 21:11
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Originally Posted by PJ2
Lost in Saigon;

The original notion posited by some was, the engines continued to run post-crash and the resultant high thrust levels from the departed engines was the reason they were so far ahead of the wreckage. I think that is an incorrect assessment of why the engines ended up where they are. What do you think?

I think the engines were simply carried forward by inertia after they broke free.

It is possible that a small amount of residual fuel kept the engine running for a second or two, or maybe just the high pressure turbine spooled down as the engine came to a stop forward of the aircraft.

As for the photo of the smoke/dust behind the engine, it could be interpreted different ways. Some one pointed out that it could have been snapped at just the right moment as the engine was still traveling forward across the ground.

I think it is also possible that there was smoke trailing out of the engine as the high pressure turbine spooled down.
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Old 2nd Mar 2009, 21:28
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Quote:
Originally Posted by PJ2
Lost in Saigon;

The original notion posited by some was, the engines continued to run post-crash and the resultant high thrust levels from the departed engines was the reason they were so far ahead of the wreckage. I think that is an incorrect assessment of why the engines ended up where they are. What do you think?
Well, maybe I'm the culprit regarding the engines...
I also think the engines had momentum from the 80-90 knt horizontal speed.
But I could not realize the engines like "balls", *if* they were rotating (not running exactly). This *is* momentum. 2.4 ton, let half be rotating mass, at what speed? They would mantain the direction at what they became loose. I could see an engine like that "ploughing" the field until the rotational momentum is lost. Or making all sort of jumps.
How long takes an engine to stop rotating, after fuel cutted out? And *if* they were at full throtle?
Relevance? Only if it helps to say what happened before. Of course there would be the data from FDR, so maybe irrelevant.
So, let us put this to rest.

Last edited by Mauersegler; 2nd Mar 2009 at 21:31. Reason: grammar
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Old 2nd Mar 2009, 21:41
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I can not completely understand all the reader comments about the High compressors and turbines vs the fan rundown.

A few things to keep in mind. The high compressor and its turbine are well burried in the smaller diameters of the engine and as such they will not often be brought to a halt due to clashing with other engine parts after the aircraft hits the ground hard (assuming of course it doesn't break the engine into pieces). Add also that the RPM difference in the high pressure rotor between idle and high power is not very much different to be able to read mechanical damage due to ground impact.

Thus the eye normally focuses on the end stages of the engine which are the last stage of the low pressure turbine and the front stage of the low pressure compressor (often a fan stage). You really are skating on thin ice if all you look at is only the front or back, because you also have to factor in whether or not parts were crushed into the blades first at the front or back.

It's realtively straight forward to interpet engine rotation speed if the engines remain attached to the airframe and take a crushing load only from the front.

This obviously didn't happen in this accident so you have to spend some time looking all over for clues and not just one or two grainy photos.

and yes I do support the posters who suggest that it's the inertia of the engines vs so little drag that lets them roll forward of the airframe once detached. I grant you that if there was zero gas path damage that the engines might be under thrust for a few seconds (El Al Amsterdam) but just the initial ground impact is likely to cause the engines to surge and lose thrust immediately (see also Piedmont B737 with one gear up landing)
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Old 2nd Mar 2009, 22:14
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Snowfalcon,

There was a woman on the radio (radio Noord Holland) who saw the airplane flying and going down.
She phoned the radio station right after the accident. She said that the airplane went up en down and up and down. Meaning the back and nose went up and down.
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Old 2nd Mar 2009, 22:24
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Old Fokker guy,
You forgot to mention that this witness/passenger hailed the pilot for his skills. And there are more.
I started my translation-post by stating I was only posting the relevant parts of the interview. Relevant as in contributing to shed some light on what could have caused this fatal crash.

I also left out that bit were this passenger stated that "he believed the pilot crashed deliberately in that field to avoid the motorway ahead" as this is also just his opinion not based on any facts. (Personally I find that statement somewhat contradictory to the events he described earlier, ie., the in his eyes normal descent/approach with the regular cabin/crew announcements and then the mere 7 - 10 seconds gap between the plane starting to sway [followed by the apparent application of full-throttle] and the ultimate crash.)
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Old 2nd Mar 2009, 22:49
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Mauersegler;

Thank you for your post and response.

The engines will have separated from the wings right at impact and will have tumbled ahead because of their weight and the momentum they had at impact which was around 80kts or so.

Engine compressor rotation will have had little to nothing to do with where the engines ended up.

lomapaseo;
Your expressed caution in re assumptions made about the condition of N2 and turbines based upon the condition of the N1 after an accident, is well said - I heartily agree.
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Old 2nd Mar 2009, 23:01
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Engines

Have a look at position of the engines relatively to the fuselage - see the photos:

Photos: Boeing 737-8F2 Aircraft Pictures | Airliners.net - both engines seen from the left relatively to the flight path, let's say engine A and engine B left to right (not necessarily # 1 & 2). Note A's spinner is clean, B has spinner covered in mud and blades bent.

Photos: Boeing 737-8F2 Aircraft Pictures | Airliners.net - this is engine A with remains of its pylon visible

Photos: Boeing 737-8F2 Aircraft Pictures | Airliners.net - engine A partially visible on the right-hand side

http://www.geenstijl.nl/archives/images/ANP-9259316.jpg - engine B (mud on the spinner).

Now, note both are on the right side of the fuselage - and the flight path. What could have moved engine #1 that far perpendicularly to the speed vector were effects of the inertia of its fan suddenly halted by crushed cowl and/or gyroscopic forces. Would a windmilling fan have enough kinetic energy to move a 2,4 ton engine that far?
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Old 3rd Mar 2009, 03:54
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Originally Posted by brandtzag
Flintstone:
Perhaps you would kindly explain "kinetic" energy an why the engines, if moving at the same speed as the airframe, suddenly appears ahead.

I'm always willing to learn something new. Especially when it comes to physics.
F=ma

Heavy things (like engines) have more momentum. Objects in motion tend to stay in motion. Objects with more mass require more force to decelerate them than objects with less mass. Its really simple Newtonian physics.

The object (the total aircraft) will act at the center of gravity until shearing forces tear the object into multiple centers of gravity. Each new center of gravity will have its own momentum. High mass (high density) objects will have a lot of momentum and less surface area and the arresting forces provided by inelastic collisions(bouncing, rolling, digging into the ground, twisting), friction and will provide minimal retardation to motion relative to the momentum.

Think feathers falling vs. bowling balls falling in air. Or 'rolling' on the ground.
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Old 3rd Mar 2009, 04:25
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Originally Posted by brandtzag
Flintstone:
Perhaps you would kindly explain "kinetic" energy an why the engines, if moving at the same speed as the airframe, suddenly appears ahead.


There are several things that would cause the enginies to be forward of the rest of the wreckage:
1. There is a centrifugal force effect that would cause the engines to be hurled forward. See post #739. High ROD with a nose high attitude at impact would cause the fuselage to rotate such that the engines move through an arc as the pitch up angle rapidly goes to zero after the tail hits the ground but before the nose hits the ground. This motion is something like a hammer swinging. If the head disconnects on impact it will move in the direction that the handle points.
2, The 41 section appears to have dug into the soft ground causing the fwd fuselage to decelerate more rapidly than the 43 Section behind it, and the engines that appear to have remained above the ground.
3. The main gears and nose gear may have penetrated the ground, at least partially, retarding the main weckage from moving as easily as the detached engines.
As far as alignment goes, the main wreckage is twisted a bit due to the effect of the seperate parts having differnet rates of decleration due to appendages such as the landing gear and open wheel wells that may have dug into soft earth.
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