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B-738 Crash in Russia Rostov-on-Don

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B-738 Crash in Russia Rostov-on-Don

Old 27th Mar 2016, 03:34
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I think that flight path of the a/c with HS in full down position (as claimed on RU tv) should be different. Definitely not a straight line - like we can observe in video showing last few seconds before impact.
But this scenario maybe coul'd fit when to presume that pilot counteracted with full column pull back.

On the other hand, to move stabilizer to full down position (f.e. with elec. stab trim) you need time - it's 30 maybe 40 wheel turns from nose up position. And on the presented ADS-B data we can see rather fast pitch drop (from +10 to -30 in 7 sec.)

So something still is very unclear in this case
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Old 27th Mar 2016, 04:28
  #842 (permalink)  
 
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Definitely not a straight line - like we can observe in video showing last few seconds before impact.
But this scenario maybe coul'd fit when to presume that pilot counteracted with full column pull back.
Exactly,yoke at full aft position at that speed and nose doesn't even raise 1 inch?...
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Old 27th Mar 2016, 04:52
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The press and some contributors seem to be making the assumption that the "Don't do that" on the CVR corresponds to some catastrophic pilot action. I'm struggling to think what could have been changed or deselected at this point in flight which was instant and irreversible.

I'm of the opinion the aircraft was still in a landing configuration at impact, suggesting a wind shear event (consistent with starting altitude and subsequent performance). This means flaps would have initially been set at flap 30. Even if the alleged pilot action was flap retraction, the initial motion would have been an improvement in performance, not a sudden stall. Any further retraction may be an issue, but it is not instantaneous, and given the apparent speeds, very unlikely at this weight to have left the aircraft at a dangerously low speed. A flap mis-selection could also very quickly be reset. Personally, I don't buy it.
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Old 27th Mar 2016, 04:55
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Originally Posted by klintE
I think that flight path of the a/c with HS in full down position (as claimed on RU tv) should be different. Definitely not a straight line - like we can observe in video showing last few seconds before impact.
But this scenario maybe coul'd fit when to presume that pilot counteracted with full column pull back.

On the other hand, to move stabilizer to full down position (f.e. with elec. stab trim) you need time - it's 30 maybe 40 wheel turns from nose up position. And on the presented ADS-B data we can see rather fast pitch drop (from +10 to -30 in 7 sec.)

So something still is very unclear in this case

Originally Posted by CodyBlade
Exactly,yoke at full aft position at that speed and nose doesn't even raise 1 inch?...
I believe the full aft yoke was totally ineffective because the tailplane had stalled due to ice accumulation.

My reasoning is due to two simple facts:

1) The aircraft flew in icing conditions for an unusually long period of time.

2) The aircraft behaved as if the tail was stalled.

Sometimes the simplest answer is the correct one.
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Old 27th Mar 2016, 05:08
  #845 (permalink)  
 
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Sometimes the simplest answer is the correct one.
There was never an accident with tail icing on the 737 so definitely it is not the simplest answer. Yes, simplest answers are usually closest to the truth, the simplest answer is totally mishandled go-around, it happened numerous times and it actually happened in Kazan, Russia barely 2 years ago. And all the symptoms were practically identical. Tail icing doesn't make sense for one simple reason - it would be at its worst during the approach with all flaps fully extended, not the go-around.
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Old 27th Mar 2016, 05:26
  #846 (permalink)  
 
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Originally Posted by Old Boeing Driver
"The television channel cited experts who suggested that by turning off the autopilot, the pilots were trying to pull the plane back to a horizontal position. But at that moment, a stabilizing fin at the jet’s tail was switched on.
With the fin activated, “the elevator is no longer working and the plane practically does not react to the pilot’s control panel,” the report said. The channel suggested that the pilot could have accidentally hit the button that activated the fin because of his reported “chronic fatigue.”"

Can anyone translate this English into English?

What could they be talking about..."a stabilizing fin at the jet’s tail"?

Edit: maybe the HS?
Never mind the b...s. These are the same people who translated the alleged CVR materials into Russian, had actors read them out against the background of artificially added "airplane-y" noises, and put the whole thing on air.

Here's my translation of what was said... for what it's worth (=nothing).

"[After the decision to go around], the aircraft was gaining altitude for 40 seconds. Not yet having reached the planned FL, the captain disconnected the autopilot for reasons unknown - possibly because of wind shear (which they call "atmospheric scissors")/rough air. It is then that the plane began to dive.

After the autopilot disconnect the captain tried to coax the plane into horizontal flight, but after the dive has begun, THE VERTICAL STABILIZER SWITCHED ON. As a result, "руль" [the word they use is actually more like "steering wheel", not "elevator" - which is what they must have meant?] stopped functioning, and the crew didn't have enough time to figure out what happened.

Why the stabilizer turned on is unclear. It is activated with a button which the pilots call "knuppel". In rough air, the captain, while switching to manual flight, might have accidentally touched it without noticing, due to chronic fatigue. Otherwise, it's some unheard of surprise on part of flight automation systems."


Last edited by Alientali; 27th Mar 2016 at 05:38.
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Old 27th Mar 2016, 05:28
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Originally Posted by porterhouse
There was never an accident with tail icing on the 737 so definitely it is not the simplest answer. Yes, simplest answers are usually closest to the truth, the simplest answer is totally mishandled go-around, it happened numerous times and it actually happened in Kazan, Russia barely 2 years ago. And all the symptoms were practically identical. Tail icing doesn't make sense for one simple reason - it would be at its worst during the approach with all flaps fully extended, not the go-around.
You make a good point, but all the other theories make even less sense as we know the pilot said "Pull, Pull, Pull" and yet there was no sign that all that pulling did anything to stop the aircraft from violently nosing over.

Tailplane icing is very rare. I doubt we know everything there is to know about it.

If the tail did stall during the late stages of the go-around, this accident could be a game changer.
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Old 27th Mar 2016, 05:32
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the pilot said "Pull, Pull, Pull" and yet there was no sign that all that pulling did anything
Have you by any chance heard of laws of Physics?
Do you know what aircraft inertia is?
They had about a few seconds, regardless of the amount of pulling in the remaining 3-6 seconds there would be absolutely no practical difference in aircraft trajectory.

If the tail did stall during the late stages of the go-around, this accident could be a game changer.
If, if, if, could ....
There are lots of ifs and coulds, not the simplest answer you are looking for.
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Old 27th Mar 2016, 05:43
  #849 (permalink)  
 
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Originally Posted by _Phoenix_
Actually, THS is moving pretty fast when actionated from trim switches, see video posted earlier
https://vimeo.com/34501723
Sorry but this vid seems not to be real, it is just physically impossible IMO
I mean that abrupt changes in angle (units), c'mon
https://www.youtube.com/watch?v=rxPa9A-k2xY thats how it works in fact

Originally Posted by _Phoenix_
I doubt PF accidentally trimmed at full ND. That's impossible; just imagine pilot experiencing impoderability, loose objects on the ceilling and he continuing with trim down.
Yes and I consider a specific dual input - trim from the right seat and yoke pull back from the left.(Or vice versa) And right seat possibly in the state of spatial-D
I know that maybe sounds bit crazy but looking at how that flight ends tells me that something abnormal happened there.
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Old 27th Mar 2016, 05:57
  #850 (permalink)  
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Klint, you are correct regarding the first video.

The correct ratio is just under 10 turns of the trim wheel per unit of trim.
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Old 27th Mar 2016, 06:28
  #851 (permalink)  
 
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Main electric trim has two speeds and that video is at the slow speed. (Flaps retracted)

The main electric trim is about twice as fast as the video shows with the flaps in any position but up.

The video does approximate the speed at which the autopilot trim motor runs with flaps up or down.
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Old 27th Mar 2016, 06:45
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The video does approximate the speed at which the autopilot trim motor runs with flaps up or down.
Not quite.The autopilot trim system also runs at two speeds ( high or low) depending on the flap position.
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Old 27th Mar 2016, 07:08
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Originally Posted by Otto Throttle
The press and some contributors seem to be making the assumption that the "Don't do that" on the CVR corresponds to some catastrophic pilot action. I'm struggling to think what could have been changed or deselected at this point in flight which was instant and irreversible.
So am I.

I would just caution against reading too much into those words; I'm surprised that no-one has pointed out one obvious possibility; that he was talking to the aircraft - hey it happens; some of us do anthropomorphize a little... it will depend on the intonation and correlation with FDR events.

R1
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Old 27th Mar 2016, 07:23
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That would be my assumption, that he was talking to aircraft, not the other pilot. Without seeing control positions and forces, though, it is anyone's guess. A stripped or sheared trim drive like the Air Alaska accident (DC9 or derivative, I think) seems plausible.
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Old 27th Mar 2016, 08:45
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Chesty,
a 737 air tester it is standard to brief the use of power to recover from an out of trim nose low attitude. Especially in a low speed scenario it is one of the first things I would consider (and it works) if my primary pitch control isn't as effective as it should be.
Especially in a low speed scenario are the key words id say.
If the combined forces of stuck down stab and high speed (due to GA thrust),i would think that releaving the forces by reducing thrust would help.
It seems that,getting back to intrim speed as early as possible,using the elevator is quite effective.
If both stab and elevator are jammed then thrust is the only help,,increase thrust nose goes up,reduce thrust nose down...
Wouldnt you say?
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Old 27th Mar 2016, 08:49
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Hi all,

My first post on this subject. Firstly, thanks to mommaklee for his outstanding work with the data.

Sorry but this vid seems not to be real, it is just physically impossible IMO
You would have to be correct, klintE. The accompanying text to that video says this: Genuine Boeing 737-300 series throttle quadrant converted for flight simulator use. That would be "flight simulator" as in the kind that enthusiasts make at home, that are based on Microsoft FSX!

This accident is strikingly similar to the Tatarstan Airlines Flight 363 B735 that crashed at Kazan, Russia in 2013. This is the graphic of the vertical profile in that accident:


Look familiar?

Earlier, someone made a reference to this article, about how the trimming systems on these aircraft work:

Roger-Wilco | Do you really understand how your trim works?

In that article, towards the end, there is this passage. Note how well it could apply to this crash, and the Kazan crash:

I have watched, in the simulator, a 737 go-around from a Cat lll fail passive approach (as described above) with its marked pitch up; HP kept his arms locked forward to contain the attitude whilst simultaneously running the trim forward with the thumb switch. I am sure he was expecting the trim to reduce push needed and he either didn’t know, or had forgotten, that it wouldn’t. We duly pitched straight back quickly into the ground as the tailplane incidence ‘bit’.
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Old 27th Mar 2016, 09:15
  #857 (permalink)  
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De facto, what is your in trim speed if you're out of trim AND? Higher or lower than your current speed?

The object is to minimise attitude change/altitude divergence (especially at low level) before you can rectify whatever problem induced the unusual attitude/out of trim position. If you have a nose low unusual attitude induced by an AND mis-trim and reduce thrust you will exacerbate the situation. Maintain or increase thrust initially, control attitude as well as you can and then deal with the problem.

Last edited by Chesty Morgan; 27th Mar 2016 at 09:55.
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Old 27th Mar 2016, 09:50
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FGD135 that profile is scarily similar, prompted me to read more about it
Wiki page Tartasan 363 details

Also interesting is the other bit at the end of understanding your trim article link,
I canít cite with certainty any accident that has been caused by doing this, but I strongly suspect this was a factor in the infamous Icelandair upset event at Oslo The aircraft went quickly from +20 deg to -40 deg and was only saved from a CFIT by a 3.5g pull up, bottoming out at 360ft. Sadly, the report does not discuss the control inputs, nor does it contain any FDR traces, so this trim confusion explanation must remain speculation. I would be astonished, however, if there werenít more examples of this error, particularly in unfamiliar situations.

Last edited by xollob; 27th Mar 2016 at 10:06.
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Old 27th Mar 2016, 10:06
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Popping in from lurking, will be gone in just a sec.

Ranger One and Aluminium Shuffler

Talking to the airplane would make sense in a way. I am totally talking to my car sometimes - confusing as it is to my passengers, LOL!

Y'all

What do you make of the strange bump in mommaklee's data? Gusts/drafts/the wrath of Mammon? Some kind of mishandling? Or just FR24 junk data?
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Old 27th Mar 2016, 10:24
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Not quite.The autopilot trim system also runs at two speeds ( high or low) depending on the flap position.

Well sort of. The high speed AP trim though is equal to the manuel electric trim speed with flaps up. The AP flaps up trim speed slower still.

From Boeing:

Normal electric trimming of the stabilizer is done at one of two rates as controlled by flap position. Trim
rate with flaps retracted is 1/3 the trim rate with flaps extended. The autopilot actuator also trims at
one of two rates as controlled by flap position. High speed autopilot rate is equal to the normal electric
low speed rate. The low speed autopilot rate is 1/2 the rate of the high speed autopilot rate.

So in manuel flight with flaps out , the trim wheel moves three times faster than depicted in the video.
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