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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 29th Mar 2016, 12:10
  #961 (permalink)  
 
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The media report said one of the crew disengaged the autopilot. Depending on the severity of the turbulence it is quite possible the autopilot could not cope and in that case it disengages without pilot action. Even if one of the pilots immediately attempted to re-engage the AP, any manually applied control wheel pressures (which could occur in turbulence) will prevent the AP from engaging. If that happens in IMC then recovery success (or otherwise) is entirely dependant on the instrument flying ability of the pilot flying. That, as they say, is another story altogether...
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Old 29th Mar 2016, 12:37
  #962 (permalink)  
 
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Originally Posted by AerocatS2A View Post
Just curious: If the 737 elevator can't be split then what happens if the jam occurs in the elevator itself?
Then you would be stuck. It is simply not a good system, and would not pass modern certification.
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Originally Posted by silvertate View Post
Then you would be stuck. It is simply not a good system, and would not pass modern certification.
This seems very strange. Would be good if someone had a maintenance manual that could confirm this is indeed how it works.
Silverstate,

If the elevators are jammed and pilots cant overpower them to clear the jam, wouldnt the stabilizer trim sufficient to fly the aircraft?
I am not sure i understand your reasoning.
NB, for the old armshair SLFs in here,it is a question to make a point,not that i dont know...before you start shivering,crying,once again,oh my god pilots dont know how to fly their aircraft
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Old 29th Mar 2016, 12:44
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Hi again all,

I have just made a posting to the Tech Log forum about the behaviour of pitch trim systems in aircraft such as the B737.

I have made reference to this accident, and the Tatarstan Airlines B735 that crashed in Kazan, Russia in 2013. These two accidents have almost identical vertical profiles. Both crashed onto the aerodrome, beside the runway, steeply nose down and at high speed.

You can find it here:

http://www.pprune.org/tech-log/57681...nderstood.html
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Old 29th Mar 2016, 12:52
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Can the black box data determine what caused the A/P to disengage or does it just see that the A/P disengaged? Can the FDR data log that the trim switches were pressed or just that the trim was operating? If I were to hazard a guess I would say the FDR cannot determine how the A/P was disconnected only that it was. Which would make leaked comments worthless.
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Old 29th Mar 2016, 13:15
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If I am correct, there was a recent computer modification available to 737NG. One of the changes is that unsuccessful attempt to engage the autopilot would cause the same indication (aural and visual) as the autopilot disconnect. If the investigators heard the AP disconnect sound on the CVR this may also prove that the crew could not successfully engage the automatics, not that they disconnected it.
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Old 29th Mar 2016, 13:26
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Yes FDR will know if stab was trimmed by AP or pilot trim switches.
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Old 29th Mar 2016, 13:52
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What if it is a trim runway and neither A/P nor manual trim switches were used. Is it a third state or an event without a corresponding trigger which has to be specifically interpreted as such by the individual(s) analysing the data?
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Old 29th Mar 2016, 13:53
  #968 (permalink)  
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In response to FAB777

Airbus have designed their FBW system to be simple in the event of a go-around. For those not familiar, you simply firewall the thrust levers - AND IT IS IMPERATIVE THAT YOU DO FIREWALL THEM. This ensure that SRS (Speed Ref System) engages with appropriate FD pitch up guidance - newer FMGC standard will also engage NAV to follow the Missed Approach procedure (assuming FLT PLAN is sequenced....!) with AP engaged it is a non-event. In the event that FAB mentioned the aircraft simply did as it was being asked to do i.e. capture and descend on the glide....as that was the mode still active. Know your aircraft!

So, it amazes me that people still fail to push the levers till they won't go any further - how much simpler could you make the system?

I'm not overly familiar with the Boeing, but from reading this thread it does seem that under certain circumstances the pilots workload can be (significantly) increased on a go-around depending upon whether it's a single/dual channel approach with pushing to overcome trim etc......

Good thread though.

A4

Last edited by A4; 29th Mar 2016 at 15:36.
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Old 29th Mar 2016, 14:28
  #969 (permalink)  

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The foregoing is one of the reasons I don't visit PPRune much any more. Those with absolutely no idea are making ridiculously wild conjectures, countered by the few who know (who then obviously give up, realising the futility of arguing with idiots). For God's sake, leave it to the investigators who will supply probable cause (unless, of course, a conspiracy theory emerges...)
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Old 29th Mar 2016, 14:30
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Just published: MAK doesn't find any evidence of malfunctions after full decipher and analyzing of FDR and CVR recordings.

MAK-IAC investigations 737-800 A6-FDN 19.03.2016

The Interstate Aviation Committee (IAC) informs that the investigation team together with UAE and USA experts continues to work on the collection and analyzing of information. The accident aircraft fragments identification and layout works are going on at Rostov Civil Aviation Factory N412 facilities.

On base of the onboard recorders data analysis there were no failures of the aircraft systems or components, and power plant failures detected. The aircraft had valid Airworthiness Certificate, received all necessary maintenance and was in working order before the last departure.

The detailed analysis of all factors related to the aircraft operation is going on. The investigation team plans to conduct necessary examinations of the aircraft control system recovered components and elements. The Boeing Company received the request for providing of the technical documentation necessary for the evaluation of the aircraft systems performance, and also the information requested related to the Boeing aircraft events with similar scenarios.

At IAC Laboratory the works on the data preparation for the mathematical model analysis and for the aircraft flight trajectory recovering supported by the audio and video reconstruction of the accident flight.

In the context of the media information with some links to the Cockpit Voice Recorder (CVR) data, the Interstate Aviation Committee states that in accordance with International and Russian air accident investigation policy the CVR data is considering as the non-public disclosure information. The IAC has not disclosed and have no intention for the disclosure of this data. The work on the transcript of the flight crew conversation is going on. Today we have more than 1 hour of flight crew conversations transcribed, including the final stage conversations. Now in the IAC Laboratory experts from UAE, RF, USA, and France are working together on this task.




Last edited by Kulverstukas; 30th Mar 2016 at 07:19.
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Old 29th Mar 2016, 15:06
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Translation of the above article frin 29 March:

The Interstate Aviation Committee informs that the commission of inquiry into the accident involving the United Arab Emirates and the United States experts continues to collect and analyze information. On the basis of the Rostov Civil Aviation Plant number 412, work is continuing to identify and "computation" fragments of the aircraft.

As a result of a preliminary analysis of flight recorders so far not revealed any failure of systems and components of aircraft, powerplants. The aircraft had a valid airworthiness certificate, passed the necessary maintenance at the time of departure was not defective.

Detailed analysis of information, aimed at identifying all the factors of the technical operation of the aircraft continues. The Commission plans to carry out the necessary investigations surviving units and elements of the aircraft control system. The Boeing Company has been requested to provide technical documentation necessary for the assessment of performance of the aircraft systems, as well as information on all the events with Boeing aircraft with similar scenario situations.

In the laboratory, the IAC continued work on preparing data for mathematical modeling and restoration of aircraft flight path with the audio-visual reconstruction of the accident.

In connection with the information appearing in the media containing data references a cockpit voice recorder, the Interstate Aviation Committee said that, in accordance with Russian and international rules of accident investigation, the information cockpit voice recorder (CVR) can not be disclosed. MAK not betrayed, and has no plans to bring this information to the public. Work on the "discharge crew talks" continues. By now deciphered more than 1 hour of negotiations, including the final stage of the flight portion. This work in the laboratory of IAC attracted UAE experts, the Russian Federation, USA, France.
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Old 29th Mar 2016, 15:36
  #972 (permalink)  
 
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The foregoing is one of the reasons I don't visit PPRune much any more.
So why have visited so far? What you were expecting? If you are only interested in the official report results, just check on the relevant websites every 3 months or so.

Last edited by lapp; 29th Mar 2016 at 15:49.
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Old 29th Mar 2016, 15:40
  #973 (permalink)  

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I will, lapp, many thanks.
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Old 29th Mar 2016, 16:07
  #974 (permalink)  
 
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PF pushing on yoke, PNF pulling on yoke, PF trims nose down to counter PNF forces on yoke. Fatigued, late at night, IMC, disoriented, this would be easy to do.
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Old 29th Mar 2016, 16:44
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Not so much as easy as unimaginable. The leak is an incomprehensible interpretation of events and people are swallowing it so readily!
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Old 29th Mar 2016, 19:29
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Furthermore, the 737Max has the same flight control system, the sole difference being the mechanical aileron - spoiler mixer unit being replaced by a flybywire unit that replicates the mechanical one with less weight. So, the system does meet modern certification.
The 737 is running on grandfather certification rights, and systems that remain the same do not have to be recertified. This does not mean these systems meet modern certification. Please correct me if I am wrong.

As to flying on stab trim. Sure. But most other aircraft have an intermediate option, between both elevators working and having to use the trimmer. It is called a proper control split. There is normally a switch or lever, and a simple pull separates one side from the other. So if a rhs control column, cabling, or elevator jams or freezes solid, the lhs system can fly the aircraft in almost the normal mode. Its called redundancy. And only after both elevators jam, do you need to use a trimmer. (And use the trimmer in the reverse sense, if it is a trailing tab trimmer. Which is confusing, but has been done for real in Manx.)

But in the 737 if one elevator jams or ices up, you lose the whole elevator system. That is not redundancy, that is 1950s technology still running 65 years later. It is like going to the car show room, and being shown a brand new Ford Popular with a new engine and dashboard. Would you buy it?


Ford releases their new 2016 model, following Boeing philosophy.
The new model has a new engine and uprated dashboard.


Last edited by silvertate; 30th Mar 2016 at 19:47. Reason: Add picture
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Old 29th Mar 2016, 19:40
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Question from the peanut gallery:

In an FBW system the FDR can record captain/FO inputs separately as a matter of course.

For 737 type, what inputs would normally be recorded on the FDR with respect to control columns, and what is recorded in the event of physical separation of some or all control column functions?

I am wondering if MAK could have hard evidence of pilot disagreement from FDR, or whether they would have to deduce that from the voice transcript.
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Old 29th Mar 2016, 20:00
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I am wondering if MAK could have hard evidence of pilot disagreement
I doubt if MAK yet told anything about such things as "pilot disagreement", "quarrel in the cockpit" or "chilling nonhuman cries" at all.
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Old 29th Mar 2016, 20:30
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Originally Posted by Kulverstukas
I doubt if MAK yet told anything about such things as "pilot disagreement", "quarrel in the cockpit" or "chilling nonhuman cries" at all.
Understood. I take the leaks with a big pinch of salt.

I am wondering what is theoretically possible to determine conclusively whenever the final report is made. Some incidents of dual inputs have been made on "the balance of probability", and not all parties agreed to the conclusions. In the case of AF447, the FDR showed in black and white there were dual (and opposing) inputs, which is possible to see because of FBW controls.

It seems to me that in 737 the control surface deflection can be recorded, but not individual control column movement which would definitively show conflict of elevator command.
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Old 29th Mar 2016, 20:59
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Originally Posted by donotdespisethesnake
Understood. I take the leaks with a big pinch of salt.

I am wondering what is theoretically possible to determine conclusively whenever the final report is made. Some incidents of dual inputs have been made on "the balance of probability", and not all parties agreed to the conclusions. In the case of AF447, the FDR showed in black and white there were dual (and opposing) inputs, which is possible to see because of FBW controls.

It seems to me that in 737 the control surface deflection can be recorded, but not individual control column movement which would definitively show conflict of elevator command.
The FDAU records parameters for the CAPT and FO control columns. Both force (push/pull) and column deflection, so conflicting inputs will easily be discovered. Parameters for the individual elevators and the aft input torque are also recorded. In addition to this there are also other sensors recorded that could be useful, Neutral Shift Sensor, Mach Trim Actuator and several stabilizer sensors. Investigators should be able to tell what was going on with the pitch control.
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