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Turkish airliner crashes at Schiphol

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Turkish airliner crashes at Schiphol

Old 5th Feb 2010, 21:59
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Originally Posted by S.F.L.Y
[ if the autopilot had bug speed priority over glideslope, the GPWS would have provided adequate warning ...]

That could have been quite useful to the medal guys as well
Maybe. Or maybe it just hides the problem for longer - if speed is maintained then you've no indication of engine problem (real or autothrust), just a slow pitch excursion to spot, in IMC... until the "what's it doing now" moment - "PULL UP"... So, not knowing your engines have failed, you pull up and firewall the throttles, and if you're BA38... nothing happens. Except you are now nose up again and losing speed, waiting for the spool-up (that isn't going to come) because the automatics hid the engine problem from you.


Does this get you better than BA38 ? I don't know. Might be an interesting experiment, but my first thought is that it still isn't going to get you onto the runway for a normal landing. Remember that unless you do that, you aren't going to do better than BA38 actually did (some pax thought it was a normal landing...). Come down any shorter than BA38 and you're in buildings or cars, go longer and you slide onto the runway and then on down it, in a shower of sparks and fuel.

To quote the guy with the medal, with the benefit of hindsight and no doubt having replayed those final seconds in his head countless times:

I have seen the figures, and wouldn't want to end up anywhere other than the BA38s' impact point... no further forward, no further back
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Old 5th Feb 2010, 23:04
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With insufficient power, you sacrifice altitude rate or airspeed. If you're already near the drag bucket, which should be on the order of 1.3 Vs, sacrificing airspeed to maintain glideslope will increase your drag - wasting precious energy - and assure you will land shorter with a higher rate of sink.

You could even draw a graph: beginning at 500 feet, on-glideslope, on-speed, power off.

Plot one line where you maintain speed while your descent rate (4 degrees, for example) is steady until reaching ground effect. You then have energy to round out in a flare. If you see obstacles, you just might have the energy to zoom up and over. Remember "Stick and Rudder"?

Plot a second line on the same graph where you maintain glideslope as speed bleeds off until stick shaker, then try to recover. You will be out of airspeed, trimmed nose up, and out of energy, with a sink rate that...

The second line is apparently what the autopilot followed on both THY and BA 038.

GB
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Old 6th Feb 2010, 00:45
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Graybeard;

Not challenging the view, and without desiring to re-open that conversation, I don't think too many fliers here disagree with the theory - it is a straightforward outcome of insufficient thrust in combination with an autopilot trying its best to stay on the glideslope. Up to the point where the airspeeds went below Vref, it was what it was for both crews. I don't believe that phenomenon has ever been in question. It just isn't relevant to the outcome of the BA038 event.

For me and I think for many, the discussion has always been about what was happening in the cockpit of THY1951 after the airspeed had gone well below Vref - fourty knots below in probably just less than 40 seconds. We both know that that is a very long time in the approach phase. The BA038 crew realized that the power wasn't coming up to maintain the airspeed and took what action was available to them with degraded engines, while the THY1951 crew did not take any action until about 400' when the airplane was around 85 knots. "How is that to be explained?", was the question at the beginning and remains so.

Cheers,
PJ2
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Old 6th Feb 2010, 03:48
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Thanks, PJ2. I wasn't trying to critique the crews as much as seeing a reason to rethink the autopilot that fails to preserve energy in the rare case of insufficient power - for whatever reason. Sure, at some point before stall, the autopilot will disengage and give the plane back to the pilot, behind the power curve, with energy wasted and with near full aft trim. Whereas, it could instead keep speed up, sacrificing glideslope beam center for max L/D.

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Old 6th Feb 2010, 06:23
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Graybeard;
Whereas, it could instead keep speed up, sacrificing glideslope beam center for max L/D.
Yup - understand.
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Old 6th Feb 2010, 08:07
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while the THY1951 crew did not take any action until about 400' when the airplane was around 85 knots.
This isn't correct. First of all the crew had a high ROD to catch the GS which was consistent with idle thrust (no action needed on the levers). When established on the GS speed normally reduced towards Vref (144kts) and crew selected it on the MCP (crew action). Following that, the AT failed to stabilized the speed which kept decaying until stick shaker (not 85 kts as you mentioned). The PF selected full thrust but the levers came back to idle. The captain took control and re-established full thrust after AT disconnection. At that point the aircraft is still on the GS and is not stalling. Unfortunately, the crew failed to readjust the trim as they lost pitch control authority due to the TOGA thrust and attitude increased until the aircraft stalls and speed drops to 85 kts.
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Old 6th Feb 2010, 10:16
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I don't know what information you are working from there, S.F.L.Y. but there are some inconsistencies in your narrative that I certainly wouldn't want to try to hash out with you. God forbid I should tell you "that isn't correct," even if that is my impression of what you have wrote.

Perhaps we really should wait for all the facts contained in the final report to see exactly what happened instead of making all these educated (?) guesses. I think that would settle many of the futile arguments we have been subjected to here, positing this or that chain of events without really knowing exactly what happened. I have been surprised more than once by reading a report that had the facts of the event contradicting my informed initial opinion and I bet this accident too has its share of surprising, unguessed facts.

Of course, part of my problem is that "the more experience you accumulate, the less you know." I bet that makes me more knowing than some here, especially the odd retired airline captain or two but far less knowing than at least one of us, an enthusiastic tyro.
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Old 6th Feb 2010, 12:15
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By chuks: I don't know what information you are working from there
Agree with chuks.

S.F.L.Y. I think you are taking on some well informed pilots, most of which have been very patient, conservative if you like, and very polite but you persist to ram home a comparison between BA 038 and THY1951 before both final reports come out.

I for one think this thread is really about THY1951 as BA038 has it's own extended thread. It's good to compare if you wish, may be start a new thread, (God forbid) but remember that both incidents involves different AC types, with extremely different AC tonnage weights! One set of weights operational the other set not operational, one AC had a three man crew whilst the other had a two man crew observing the controls. Both incidents involved high volume ATC interaction, but the approach was perfectly normal for BA 038 until that last powerless 50 seconds or so whilst THY1951 has some ATC issues that may or may not be involved in the final report. This thread FOR THY1951 and the BA038 thread have comments included by actual pilots that were there or close by at the time of both incidents. They have more than convinced me that I should wait for the respective final reports.

At this stage, I am confident that these final reports for both incidents will conclude completely different circumstances as much as they may sound similar today.

S.F.L.Y. with respect, I think my simplistic post is what many far more experienced pilots than I have been trying to say to you!
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Old 6th Feb 2010, 12:27
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If I can help gently untwist the knickers again?
Originally Posted by chuks
I don't know what information you are working from there, S.F.L.Y.
- it is called the Preliminary Report published by the Netherlands Aviation Safety organisation, and apart from PJ's '85kts' which is not mentioned in this later report, it is all there - on page 3 in fact. Maybe worth reading?

The lowest speed I can find mention of (and this is thanks to Dutch Bru's translation of the Dutch initial report) is 175kph at impact - roughly 97kts. No mention anywhere there of 85kts.

Last edited by BOAC; 6th Feb 2010 at 12:39.
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Old 6th Feb 2010, 12:48
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S.F.L.Y. may compare whatever he/she likes.

The facts are

- BA 038 both engines dead - no fatalities
- THY 1951 both engines running - nine fatalities
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Old 6th Feb 2010, 12:49
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BOAC...

Do you mean the Dutch Safety Board preliminary report of 4 March 2009 or are you referring to another report there? I have read that preliminary report several times if that is the one you are referring to and I do not find some of the stuff that I would need to draw the same conclusions reached here by others posting, hence my wish to wait for the final report.

For instance, the preliminary report reads that the localiser was intercepted at 5.5 miles when that would obviously seem to be a bit too high for a tidy intercept, yes. What we still don't know from that, though, is what exactly Dutch ATC told the accident crew to do, what role the ATC clearance given played in the late, high intercept that might well have contributed to this accident with an obviously unstabilised approach.

I am keeping an open mind about a lot of this and it is simply that I would like to see all the information, much more than is in the preliminary report. There you have quite a bit about what happened (from the FDR, I assume) but nothing about why it happened, when that is the part I really need to know. Of course the Dutch Safety Board needs to deliberate on that in collaboration with the Turkish and U.S. authorities before they can tell us that, while the FDR data was easy to read out and report on.

Last edited by chuks; 6th Feb 2010 at 13:10.
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Old 6th Feb 2010, 13:14
  #2672 (permalink)  
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You took SFLY to task somewhat over post #2577 (31/1/2010) but obviously missed the report?
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Old 6th Feb 2010, 16:07
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There have been two DSB releases, 1) a press statement on March 4 and 2) a prelim report on April 28 and here are the links:

http://www.onderzoeksraad.nl/docs/ra...4_March_GB.pdf

http://www.onderzoeksraad.nl/docs/ra...ary_engels.pdf
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Old 6th Feb 2010, 16:33
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Some light in the darkness...

I read these two things but mistook the date of the preliminary report for 4 March 2009, the date of the press release. Kiittos! (Well, something like that, anyway.)

"Taken to task," well... If someone needs to treat a bare, factual report like a Christmas tree to hang it with tinsel and strings of little blinking lights and then invite us all to admire his handiwork perhaps he should expect some of us to be left cold by this accomplishment. "Vz," indeed...

The report tells us, for instance, that the accident crew intercepted the localiser at 5.5 nm. That is obviously very tight so that the next question must be "Why did that happen?" Were they following an ATC clearance that required that outcome or did they have, perhaps, too high a speed (when these are two things that might lead to this outcome from which we should draw very different conclusions)?

A good report has a high signal-to-noise ratio, so to speak but lots of the stuff I am reading here is mostly just noise so that I tend to tune it out.

Is there a date promised for the final report?

Last edited by chuks; 6th Feb 2010 at 17:20.
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Old 6th Feb 2010, 17:04
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Chuks.

The report tells us, for instance, that the accident crew intercepted the localiser at 5.5 nm. That is obviously very tight so that the next question must be "Why did that happen?" Were they following an ATC clearance that required that outcome or did they have, perhaps, too high a speed (when these are two things that might lead to this outcome from which we should draw very different conclusions)?
Outsider here and not familliar with Schipol, but I've read virtually everything on this thread since the day of the accident. Without going back through a great many posts to verify, I have the strongest recollection of THY1951 being vectored originally to a different runway and shifted to the destination runway by ATC.

If that is wrong, my apologies.

Roger.
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Old 6th Feb 2010, 17:04
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BOAC;

Thanks for the correction. I'm not making this discussion the focus of my life and I'm going from memory on the speed. Likely the "85kt" came from the report of the Thompson B737 stall from which the crew did recover.

But....., "85kts"...."97kts", the essential point, and the outcome, are the same. For whatever reason, the salient fact here is, over a time period of 100 seconds the aircraft was permitted to lose more than 40 kts of airspeed in the very late stages of the approach phase.

We will have to wait for the report to provide more information such as the CVR and DFDR and for the Dutch Board's conclusions as to why this was allowed to occur.

Last edited by PJ2; 6th Feb 2010 at 21:34. Reason: keeping on topic
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Old 6th Feb 2010, 17:32
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Framing the Facts

PJ2
For whatever reason, the salient fact here is, over a time period of 100 seconds the aircraft was permitted to lose more than 40 kts of airspeed in the very late stages of the approach phase.
Not wanting to pick on you, PJ2, but your post was most handy. Would it not be more better to say? "For whatever reason, the salient fact here is, over a time period of 100 seconds, the autopilot caused the aircraft to lose more than 40kts of airspeed in the very late stages of the approach phase, in the attempt to stay on glideslope, and neither the autothrottle nor the crew intervened.."

I have become sensitive to the framing of arguments, thanks to divisive US politics.

GB
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Old 6th Feb 2010, 18:14
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To each his own

The insistence that accidents must have some commonality? At some stage, the paradigm is crested, separation of systems is impossible. What is needed is a safer recognition of and reversion to manual control. A perfect system is impossible; on landing, relying on A/P to maintain altitude (or slope) is a tricky proposition. This is a very fine endeavour, at a time in the flight when safety margins evaporate, as they are intended to. Similarity?

How about Colgan's trim wheel? 447's flight into upset? Auto pilot and dependence thereon? 038? Who needs to keep the glideslope without power? At some point in every flight, there must be a firm and well annunciated transition to mode of flight. What's it doing now? 400agl? Marvelous time to ask the question.
 
Old 6th Feb 2010, 18:23
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Come on guys, let's put it straight.

Regardless if the auto flight system or the PF lost 40 kt during final approach, the COMMANDER or PNF failed to react!

Isn't it SOP in most companies to call out a speed loss of - 5kt during final?

No reaction on call out? Take over! Very SIMPLE!

END
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Old 6th Feb 2010, 18:31
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...they pick up on minutae, find a grain of truth from which to extrapolate a grand argument or theory, challenging everything that is offered in rebuttal until the responder tires of the game. To what end? I have read almost all his posts and I believe that SFLY is in no position to offer advice to veteran airline pilots and is certainly in no position to admonish or lecture those who are actually doing the work.

I respect SFLY's 3000 hrs of military turboprop & turboshaft experience, and imagine his high COF method of interaction here is the result of a long, frustrating hunt for work in the commercial sector.

He has been hearing about it for quite a while. Here are comments to a post of his a year ago:


SFLY
Brew yourself a cup of Camomile tea (in the pot, not cup), put Enya on the iPod, remove slippers, get a foot rub and chill out.
Alternatively, try getting out of bed on the otherside tomorrow morning.

S.F.L.Y., let us old farts reminisce without the newspeak lecture. Like all old farts, we have selective memory, recalling only the good bits, (as everyone should when talking about 'the old days'), and believe me, while doing so, we don't need some young whippersnapper mounting his electronic soapbox to lecture us in 2009 managementspeak.
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