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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 26th Mar 2016, 21:13
  #821 (permalink)  
 
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Having followed this thread and read all the posts my feeling is that this is more than a mishandled go around, whether or not the autopilot was in use.

Even fatigued pilots know how to fly a go around and these pilots were not beginners.
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Old 26th Mar 2016, 21:23
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Xollob

I originally thought this might be a high speed event due to the light airplane with loads of power.

However, I think Dave Reid pointed out that one of the last GS plots was 185KTS. As they started down, GS increased.

With very little info, we are all still guessing and speculating, but the Bournemouth incident made me think of another scenario.

If it was me, I would have gotten the automation back on after the GA and clean up due to the fatigue factor and I would want to monitor all that was happening.

It looks like they had a high ROC right after the GA. If the PF had turned on the automation, and idled the power, he may have be looking at other things well into a speed degradation (like Bournemouth) until the plane was actually stalling.

In the Bournemouth incident they had a 44 degree pitch angle. The same or more could have happened here, and maybe when the break occured, then they may have had the power all in and never touched it as they tried to recover.

IMHO, it would be difficult to get descending at 18,000 FPM in just a few seconds without the power helping.

Just another scenario to consider. We'll know when the FDR and the full CVR info is published.

Last edited by Old Boeing Driver; 26th Mar 2016 at 21:57.
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Old 26th Mar 2016, 21:38
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If they engaged the AP on the miss it's the AP trim motor that runs the stab. It runs slowly and it is normal to hear it during that circumstance. It would be trimming nose down almost certainly. If they engaged it during a highly dynamic situation the system can't keep up often times and begins pitch oscillations. If they turned off the AP in response to a pitch up oscillation with the AP still trimming nose down, they might have got a big pitch over surprise as the AP disengaged. We all need more information obviously. Just throwing this out there.
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Old 26th Mar 2016, 21:50
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I couldn't see if it had been mentioned yet or not, so perhaps someone can link to it, or our weather guys could shed some light on the wind changes within the altitude band we're looking at. The wind speed has been mentioned at 600m as being somewhere in the order of 60-70 kts if I recall, but not direction.

On the surface, the wind appears to be fairly steady directionally from 250 degrees, so a crosswind from the right (runway 22), so assuming it veers with altitude, it becomes a stronger, more direct crosswind. This doesn't fit with a rapidly increasing headwind scenario, as the change in direction would to a large extent cancel out substantial changes to headwind component. If the direction remains steady however, then that theory holds water.
The best wind data available is from the Airport's Sounding taken at ~0000 UTC 19MAr16. Here are the data for the relevant lower altitudes:



Speed drops near the surface in what one would expect would in power-law fashion, with increasing gustiness, while backing 'gradually' from ~westerly to ~southwesterly.

I took a stab at calculating head winds and cross winds for the second GA:



with an corresponding GPS altitude chart which also includes a stab at IAS:



I hope that helps some.

(Sounding data: University of Wyoming - Radiosonde Data)
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Old 26th Mar 2016, 21:55
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737er

Good points. It's been a long time since I flew the 737, but can remember a few surprises as you mentioned.

I really want to know how it happened so fast.

Regards.
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Old 26th Mar 2016, 21:57
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While I am posting images, I fixed up a comparison of the two GA attempts, with time zero being the first indication of pitch up in the single station ADS-B data from FR.



and



FWIW.

The difference between 17 and 30 sec is very curious to me, but I don't know enough to speculate as to what it indicates.
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Old 26th Mar 2016, 22:15
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Mommaklee

How did you calculate the IAS?
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Old 26th Mar 2016, 22:41
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how does the plane go from 0 to 45-90 bank angle without lateral deviation ?
It would be possible, when it is unloaded...
In other words, when AoA is such that it gives minimal lift. In that situation, there will be almost no lift vector and, hence, nothing to pull the AC into the turn.
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Old 26th Mar 2016, 22:46
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Originally Posted by Old Boeing Driver
How did you calculate the IAS?
I converted vertical speed from FPM to knots, then calculated the hypotenuse (vector if you will) speed. A year ago or so I ran across a reference which gave as an estimation between TAS and IAS: (TAS/(height_in_ft/50000+1)) [don't have the link handy as it is on my work computer]. From that I roughly estimated at the altitudes in question TAS~= the above calculated speed + head wind. All quite rough, not having an E6B.

If I can improve upon that given the FR24 and sounding data, I would love to do so!
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Old 26th Mar 2016, 22:58
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Originally Posted by flyingchanges
"B737 trim does not work the same as small aircraft trim. In small aircraft you trim out the forces. But in B737 which has THS, you do not necessarily trim out the force. As a matter of fact, you can have the control column in neutral position with no force, while the THS is being trimmed hard forward and not feel anything on control column."





Actually to some degree, this is true. You still trim out the control column forces, but for the most part, the yoke remains centered when trimmed. In a light ac, you are changing the position of the elevator and yoke with trim changes.





Trimming the stabiliser versus the elevator is the difference.
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Old 26th Mar 2016, 23:08
  #831 (permalink)  
 
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Mommaklee

Well done and explained.

I think your calculations are pretty close.

They accelerated from 200KTS to 300KTS in about 7 seconds.

Airspeed, Altitude, and ideas are the basic requirements of flight. You have to have 2 of the 3 to be relatively successful.

It looks like they ran out of ideas and altitude too late.

Thanks for your posts.
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Old 26th Mar 2016, 23:45
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Tangent "Headwind"

Mommaklee,

Once you're in a steep climb or descent, there's an extra tangential "headwind" component which has to be brought into the headwind component calculation.

IAS and TAS will be along the hypotenuse while GS is generally given along the horizontal component.
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Old 27th Mar 2016, 02:07
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Originally Posted by mommaklee


What might be enlightening is to annotate that plot with the reported (and time-correlated) CVR remarks...

R1
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Old 27th Mar 2016, 02:13
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Just what we do NOT need is an article from the NYT- via seattle times

Transcript indicates cockpit decision may have doomed FlyDubai jet that crashed in Russia | The Seattle Times

By IVAN NECHEPURENKO
The New York Times

MOSCOW — An error by a crew member committed during adverse weather may have been responsible for the crash of a passenger jet last week in the southern Russian city of Rostov-on-Don that killed 62 people, a report broadcast by Russian state television said.
The Rossiya-1 television channel said it had obtained a transcript of the pilot interactions a minute before the FlyDubai Boeing 737-800 passenger jet nose-dived to the ground, killing all the passengers and crew members. A source in the investigative commission with access to flight recorders provided the TV channel with the transcript.
Goes on to claim wrong button was pushed re trim of HS or some such- eg pilot error..
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Old 27th Mar 2016, 02:30
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You cannot trim down in the NG while there is control wheel backpressure in manual flight. Which is what you would naturally do to keep your attitude.
Yes.But activating the under-floor cutout feature requires a pronounced opposing stick force.
If accidental nose down trim went unchecked for longer than say,several seconds at that altitude,they wouldnt have had a lot of room to play with.It remains a possible scenario.More data is needed to narrow it down.
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Old 27th Mar 2016, 02:41
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NYT Article

This is a quote from the NYT article.

"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?
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Old 27th Mar 2016, 02:42
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Never flown a Boeing but many years flying various FBW bus's.

Reading the comments here about pilots mishandeling trim and speed and pitch difficulties during GA makes me think more airlines should be buying A320's instead of 737's.
Yes, because the best solution for pilots loosing basic stick and rudder skills is to just put a computer to do that for them... And we know how that turned out with AF447...
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Old 27th Mar 2016, 03:01
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What could they be talking about..."a stabilizing fin at the jet’s tail"?

Edit: maybe the HS?
Just a SWAG from this SLF. Much confusion in many- MOST - press accounts between what is the ELEVATOR and what is the HORIZONTAL STABILIZER.
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Old 27th Mar 2016, 04:00
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The NYT article doesn't make any sense.

They can't diffenciate between 'fin',HS and stab.
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Old 27th Mar 2016, 04:20
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What might be enlightening is to annotate that plot with the reported (and time-correlated) CVR remarks...
I am not particularly confident in the veracity and completeness of the CVR transcription as provided in the media thus far, It is what we have for now and worth discussing. With that...



(I updated the IAS calc using the method suggested here: http://www.pprune.org/tech-log/44986...ml#post6419000 -- Found that just after my reply to OBD. (Thank you by the way for your kind words. They were very much appriciated ))

Also, for what it's worth, remember the cloud base was in the vicinity of 1700 ft above *MSL* (I am using GPS altitude in these plots).



These annotations may also be helpful here:



with



for comparison.

The period ~18 to ~30 seconds after the initiation of the second GA in the last two has stood out to me over the past couple of days as interesting, but I don't know what to make of it myself.
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