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Pegasus Airlines Boeing 737-800 TC-CPF overrun runway at Trabzon. All pax okay

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Pegasus Airlines Boeing 737-800 TC-CPF overrun runway at Trabzon. All pax okay

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Old 14th Jan 2018, 12:10
  #21 (permalink)  
 
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Originally Posted by Podcast View Post
really... oh come on, how's that possible ?!
Humans' inability to accurately discern acceleration/deceleration forces is well documented. It's the basis on which all full-flight simulators work.
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Old 14th Jan 2018, 12:15
  #22 (permalink)  
 
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Originally Posted by Old King Coal View Post
Some might of course retort that BKN (Broken cloud) is not a 'ceiling'. However, if the bit of sky that you're in is also the bit with the BKN cloud in it (and remembering that BKN = over half the sky) well go figure the view out of the window?!
I believe it's the case that it is defined as a ceiling when the cloud cover is 5-7 oktas (BKN) ... open to correction

Regarding the feeling of acceleration towards the end, apart from bodily sensations, could the power and noise of the reverse thrust have aided this illusion? The reverser doors are submerged in water in the images shown in all articles I've seen so can't even make out if they were open at the time of sliding
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Old 14th Jan 2018, 12:19
  #23 (permalink)  
 
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OK. Here’s my GUESS.

The boeing was at very low speed when it went over the edge. Had it still had high speed, it would not have ended resting on the steep slope towards the sea, but IN the sea! The skid mark that can still be seen on the runway (picture below) already has a large angle from the runway centerline.
So here's what I THINK COULD have happened: The a/c was rolling at taxi speed toward the turn pad at the end of the runway, when suddenly there was a technical malfunction (NWS, left brake suddenly fully blocked…) causing the a/c to veer to the left. And just before it stopped it rolled over the edge.

I can’t wait for the official report to be released (hoping we ever get to see one )

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Old 14th Jan 2018, 12:21
  #24 (permalink)  
 
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Looking closely at the photo, you can see a short skid mark from what was probably the left gear and it’s angled quite a bit off the runway direction. For an aircraft with ABS, that’s an interesting thing to see...

Edit: Crossed with sabenaboy. I agree with everything he says. It does make the possibility of some kind of malfunction more likely, as opposed to mishandling, so I think we should give the crew the benefit of the doubt for the time being.
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Old 14th Jan 2018, 12:30
  #25 (permalink)  
 
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Yeah, I'm just an SLF, but my intuition agrees with Sabenaboy - landing went ok, plane slowed on plan, pilots retracted buckets and decreased braking because they decided they were at taxi speed, which is where the passengers felt "acceleration", and then some steering malfunction or pilot error happened and then it went so fast and the airframe had so much residual energy that physics took over. I wouldn't blame this on bad landing execution, although it is quite possible some pilot error did occur on the ground.

A lot of people here -pilots- talk about the necessity of ensuring safe landing parameters for a potential go-around in the event of an engine issue, but no one ever speaks about safe taxi parameters to recover from a mechanical issue during taxi.

Obviously this runway is a really bad place for a runway excursion. Luckily Murphy seems to have been on lunch break.

The voice recorder in this one will be really interesting.
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Old 14th Jan 2018, 12:31
  #26 (permalink)  
 
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So here's what I THINK COULD have happened: The a/c was rolling at taxi speed toward the turn pad at the end of the runway, when suddenly there was a technical malfunction (NWS, left brake suddenly fully blocked…) causing the a/c to veer to the left. And just before it stopped it rolled over the edge.
Happened before. Nose gear deflection on landing roll which initially can be compensated by rudder but not at low speed.
nosegear malfunction due to birdstrike
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Old 14th Jan 2018, 12:45
  #27 (permalink)  
 
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I read a very interesting article in the internal BA pilot safety magazine last year alerting pilots to a phenomenon that I had never even thought of before. Quite often the aircraft has slowed to "reversers stowed" speed, say 60kts well before the end of the runway and then, because such as here, there is some way to the end, kept at a relaitvely high speed to expedite the landing. Suddenly the end of the runway comes up faster than expected and the PIC panics and hits the brakes hard. I am wondering if that is what happened here followed by some sort of lock-up or aquaplane.
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Old 14th Jan 2018, 12:46
  #28 (permalink)  
 
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Just a speculative thought

- the aircraft apparently departed from taxi speed, to the left of the runway
- the right engine is in the sea, the left engine is still attached to the pylon

Any potential for some kind of power increase on the right being a contribuing factor?

It could also help to explain the perception of acceleration (though earlier posts have commented on other reasons for that).
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Old 14th Jan 2018, 12:53
  #29 (permalink)  
 
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They we're going to make a 180 degree turn on the runway at some stage.
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Old 14th Jan 2018, 13:09
  #30 (permalink)  
 
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Something caused the aircraft to suddenly swing left 35/45 degrees. The port wheels skid mark show the aircraft was travelling in a straight line when the wheels locked up for a short distance then rotated again before crossing the runway edge, which is skid mark free. I suspect there might have been a problem with the nose-wheel steering. For the captain's sake I hope so.
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Old 14th Jan 2018, 13:09
  #31 (permalink)  
 
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Originally Posted by FullWings View Post
Looking closely at the photo, you can see a short skid mark from what was probably the left gear and it’s angled quite a bit off the runway direction. For an aircraft with ABS, that’s an interesting thing to see....
Indeed. But if the brakes locked up, you would expect a double-black line parallel to the runway, and then making an excursion to one side. A short brake lock-up at 45 degs to the runway is odd for so many reasons.

Its position might suggest a controlled excursion to the right side of the runway, before the big excursion to the left. As if making they were making the 180 to backtrack at too high a speed. But the brake lock-up is still odd.

Last edited by silverstrata; 14th Jan 2018 at 17:04.
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Old 14th Jan 2018, 13:11
  #32 (permalink)  
 
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B737NG Anti skid cuts out at very slow speeds.. I'll leave it at that. I would put my money on a perfectly servicable aircraft, long landing, heavy manual braking and when they reach 18kts, the anti-skid cuts out, he locks the left wheels and off he goes.

Off to the bookies now.
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Old 14th Jan 2018, 13:25
  #33 (permalink)  

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Red face

4.5% go-around gradient = 386 ft decision height.
For a B737 it's ...
The OEI G/A performance is markedly better than 5% grad, not an issue. Ergo BKN 400 ft not an issue.

Not that it would had antything to do with an almost 20 veer-off 2400 m down the runway anyway.
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Old 14th Jan 2018, 13:26
  #34 (permalink)  
 
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Originally Posted by RVF
and when they reach 18kts, the anti-skid cuts out, he locks the left wheels and off he goes.
If he were at 18 kts at that point of the rwy, that would be a very normal speed. There would have been no need for heavy braking. What happened remains a mystery.
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Old 14th Jan 2018, 13:28
  #35 (permalink)  
 
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It must have been a very challenging evacuation. Kudos to the cabin crew.
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Old 14th Jan 2018, 13:31
  #36 (permalink)  
 
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Post 23 Quote-
The skid mark that can still be seen on the runway (picture below) already has a large angle from the runway centerline.
-Quote


I cannot see any skid marks on the runway. Watching the video posted earlier you can see two people walking along the runway and that is what is being mistaken for skid marks.
This photo is taken from the beginning of the video.
Attached Images
File Type: png
plane2.png (238.0 KB, 691 views)

Last edited by LongJohn54; 14th Jan 2018 at 13:45. Reason: Numbered the quoted post
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Old 14th Jan 2018, 13:35
  #37 (permalink)  
 
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VERY well spotted. Hmm. makes it look more fishy indeed.
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Old 14th Jan 2018, 13:58
  #38 (permalink)  
 
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I was about to say nonsense, but looking again at the picture in #23, it could be two people standing that I originally took for skid marks. And the line-up on those 'marks' don't seem to exactly match the subsequent 'obvious' wheel marks in the mud - but that could be just a perspective issue. Hopefully the full investigation (there will be of course?) will reveal more.
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Old 14th Jan 2018, 14:01
  #39 (permalink)  
 
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The skid mark clearly shows the LH wheels were locked up at the point it departed. As for it being "taxi speed" complete nonsense, 737 would just stop at 15KTS taxi speed. The turning circle is to the RHS of the runway and there is no need to turn left before turning right the 737 can easily do this, even 747 land at Trabzon. Boeing perf tools give 1956 M with AB3 F30 and 1792M AB3 F40 at 63Tonnes with Anti Ice. ( landing weight based on ZFW plus min fuel and 162 pax). Nose Wheel steering is a low speed regime and won't cause the brakes to lock, so that's a red herring. The sensations the PAX describe of "speeding up" may equate to when the AB were disarmed. Non-standard RW CL lighting can be confusing. Deep landing with heavy left foot after disarming AB seems most likely, sadly. Several Turkish websites commenting on the "company culture" of putting crews under pressure. Notwithstanding any of this, our sympathy is with the aviators and we must remember we are all human.
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Old 14th Jan 2018, 14:03
  #40 (permalink)  
 
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Yes, LongJohn54. Well spotted. There goes my speculation.
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