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An-148 missing after takeoff from Moscow

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An-148 missing after takeoff from Moscow

Old 17th Feb 2018, 12:08
  #181 (permalink)  
 
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Originally Posted by safetypee
Re AAKEE, is the AoA heating part of the pitot heating system?
Nope.

But is a good help if ASI fails. If AoA shows normal values during 1G flight( and not very high AoA) the speed can not be low, provided you still think AoA information is valid. AoA-information should be very easy to check that it is not "frozen" on the same value.

Not that there most certainly was enough information to continue fly anyway.
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Old 17th Feb 2018, 13:26
  #182 (permalink)  
 
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wiedehopf

Imo, in certain cases GPS can give invaluable information. Yes, it's a ground speed you will see there, but in this particular case of low altitude flying, even with crazy wind fluctuations, you could at least avoid STALL by maintaining around 250-300 kt GS, which in theory should give you some safety margin even in clean configuration.

Then power and attitude.
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Old 17th Feb 2018, 18:22
  #183 (permalink)  
 
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Isn't GPS is decent backup source for altitude data as well? In case of trouble on the primary instruments, like the frozen ports, it seems to be an alternate source of information that is read out in a completely independent and unaffected way.
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Old 17th Feb 2018, 18:27
  #184 (permalink)  
 
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Assuming that HAE is available to the crew. Is it?
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Old 17th Feb 2018, 19:00
  #185 (permalink)  
 
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Sheppey,
Thats great information about a stick shaker going off.

According to
Antonov An-148 Passenger Transport Aircraft - Aerospace Technology

"The An-148 features a partial glass cockpit which can accommodate four crew members. The cockpit is equipped with five 6inื8in multifunction LCDs developed by Aviapribor and fly-by-wire flight controls."

The flight profile shows a cycle of climb and descent, and assuming GPS AirSpeed and GPS ground speed were displayed, at least one pilot may have freaked out at seeking zero air speed and kept lowering the nose to see what he wanted to see, "airspeed" and then rather than checking or listening to the other crew, became even more convinced of his own false narrative.

It makes you wonder how they can build a Fly By Wire aircraft and then have a "partial glass cockpit" when all the components of an AHRS system are available on E-bay.


Even if we ignore the "transcript" of the CVR, then there is still a failure to use the check list which would have mentioned the Pitot Heat and or Pitot Heat Failure, and assuming separate systems from left to right, it also has all the hallmarks of a captain seeing what he wanted to see etc.

That's not unique to the Russian Culture where fear terror and intimidation is found as normal on the dark side of Russian culture.
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Old 17th Feb 2018, 20:00
  #186 (permalink)  
 
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Fly-by-wire again?

What kinds fly-by-wire(FBW) system are we talking about?

Way too many loose references to FBW and not enuf details. Many planes have had electrical and electro-mechanical connections to the control surfaces and such for 50 years. Dampers, "control augmentation", control stick steering and the beat goes on. But few have had true fly-by-wire with zero mechanical connections from the yolk/stick to the ailerons, elevator and so on. Many, if not most jets from the early 50's drove the flight controls with pure hydraulic pressure or a combo of hydraulics and cables/pushrods. That ain't fly-by-wire. Electronic limiters and inputs that supplement basic hydraulic/mechanical implementations ain't FBW.

So the crew of the ill-fated plane may have turned off the autopilot, but what did the FBW system do? Was the system still using the bad air data? Were they in "direct control" as with the arbus implementation?

I have a very hard time understand a prolonged 30 degree dive until impact. I only saw that kinda pitch angle when delivering ordnance or performing aerobatics.

The scenario deeply disturbs me, and not just because the crew didn't turn on the heaters. The probes could have frozen anyway or ice crystals in the lines could have made things crazy. Oh well.......
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Old 17th Feb 2018, 20:30
  #187 (permalink)  
 
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It's true FBW system with mechanical backup. Pilots only switched off AP (as we can understand from IAC report). To get "direct control" they had also switch off Electronic Steering System with overhead switch. Without doing this they still faced interfering electronic system, that regulated steering effectiveness relating on unreliable speed data.
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Old 17th Feb 2018, 22:24
  #188 (permalink)  
 
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I do wonder about that overhead electric steering mode switch.

I didn't mention heading at any point in my analysis Kulverstukas as it never varied from a track of 045 even after they had gone manual and were fighting with the aircraft. Limited my comments entirely to pushing and pulling.

Rob
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Old 17th Feb 2018, 23:03
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Originally Posted by gums
I have a very hard time understand a prolonged 30 degree dive until impact. I only saw that kinda pitch angle when delivering ordnance or performing aerobatics.
The scenario deeply disturbs me, and not just because the crew didn't turn on the heaters.
Idem the lunatics that crashed perfectly flyable a/c in Perm, Petrozavodsk , Sochi 1, or Sochi 2 (*RA-85185), or DME (RA-85744).

What were they thinking? Brains not in gear?
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Old 17th Feb 2018, 23:36
  #190 (permalink)  
 
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I appreciate comments from amateurs can at times be valuable but this is just plain wrong and insulting.
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Old 18th Feb 2018, 00:01
  #191 (permalink)  
 
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Thank you, Flash. Was thinking same thing about previous post.

I raise the FBW issue after seeing a few thousand posts about the Airbus FBW and the layers of reversion modes. Thanks to Kulvers once again about a hint of this plane's system, so it does seem possible to eliminate at least some of the computer commands that are based upon air data and body rates and even attitude ( Airbus pitch and roll correction to the gee command).

The biggie is how much "authority" the human has versus the machine laws. Did the crew even try to revert to a semblance of hydraulic/mechanical control?

My point is that the crew may have been facing a more complicated scenario than several here have assumed. A straightforward pitot/static failure on older systems was not real hard to handle. This is not so with the FBW systems, as we saw with the "not to be referenced thread".
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Old 18th Feb 2018, 00:13
  #192 (permalink)  
 
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I have a very hard time understand a prolonged 30 degree dive until impact. I only saw that kinda pitch angle when delivering ordnance or performing aerobatics.
It happened to the FlyDubai Boeing 737 too. Steep dive after a go-around not helped by the pilot holding full forward stab trim all the way down.
See:

https://en.wikipedia.org/wiki/Flydubai_Flight_981
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Old 18th Feb 2018, 03:46
  #193 (permalink)  
 
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Originally Posted by Martin_123
It does actually.. pictures on the Russian forums are floating around with very prominent yellow warning messages displayed on ECAM should the heating be off or failed
THIS I dont get. its supposedly a dark panel, right?? i mean, yellow isnt supposed to be there. is it?
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Old 18th Feb 2018, 06:51
  #194 (permalink)  
 
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Originally Posted by PPRuNe Towers
I didn't mention heading at any point in my analysis Kulverstukas as it never varied from a track of 045 even after they had gone manual and were fighting with the aircraft. Limited my comments entirely to pushing and pulling.
The track of 045 is just FR24's incorrect interpretation when, as in this case, an aircraft sends zero values for the two ADS-B airborne velocity components (N-S and E-W).

The absence of any groundspeed in the ADS-B data, once airborne, is for the same reason.
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Old 18th Feb 2018, 08:10
  #195 (permalink)  
 
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Originally Posted by PPRuNe Towers
I do wonder about that overhead electric steering mode switch.

Rob
Under "steering" I also mean pitch and angle control, which is affected by airspeed through FBW which changed coefficient of effectivenes on column move.

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Old 18th Feb 2018, 08:21
  #196 (permalink)  
 
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Originally Posted by gums
This is not so with the FBW systems, as we saw with the "not to be referenced thread".
Plausible scenario for me right now is not "pilot dive the plane to regain speed" but after they recognize malfunction and switched off AP, PF makes "small moves" to check if plane is still under control, hence "level flight with +/- 05G overload" from MAK report, but probably one move - amplified by wrong speed data - put them out of range of recovery.
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Old 18th Feb 2018, 08:44
  #197 (permalink)  
 
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I don't get it anymore. Why we have pressure censors under toilet seats but Pitot tubes are "Trust me i am OK" instrument?
I swear with my electrical engineering diploma, you need like 20$ investment (20000 with certification and such) to install the device which can inform pilots about ice buildup inside a tube.
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Old 18th Feb 2018, 08:49
  #198 (permalink)  
 
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They are not. In this case they have plenty of warnings, starting with yellow "[HEATER IS OFF]" on the middle screen and following with red "[SPEED COMPARE]" twice with added sound effects.
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Old 18th Feb 2018, 08:57
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With all respect.
There is fine line between the data you need to process through your mind and clear malfunction warning.
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Old 18th Feb 2018, 08:59
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Originally Posted by gums
The scenario deeply disturbs me, and not just because the crew didn't turn on the heaters. The probes could have frozen anyway or ice crystals in the lines could have made things crazy. Oh well.......
Unfortunately, to me it sounds like typical swiss cheese hole scenario:

1. Airplane type has manual pitot heat (first hole)
2. Tired crew forgets to turn them on (another hole)

speculations:
3. Pitots start freezing at worst time (climb-out, going through possible precipitation, third hole)
4. *Indicated* airspeed starts declining, pilots do what pilots tend to do: keep speed alive. "Speed is life". Full power and stick forward to regain the airspeed. "we do not want to stall"
5. Being on climb out, there is very little time and height for crew to recognize the underlying issue. A/C overspeeds. Nose is tucking down (or Ukranian FBW is doing funny things based on unreliable speed input) and stick starts to loose authority. Lot's of alarms are sounding (I bet stall alarm was blaring at the same time as A/C was overspeeding, adding to confusion).
6. At low height, there is no time to regain control and A/C augers in.


FBW or not, all kinds of bad things can and will happen with unreliable airspeed if you are caught in bad moment
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