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Challenger crash at KASE

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Challenger crash at KASE

Old 22nd Jan 2014, 17:47
  #201 (permalink)  
 
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Hard to tell given it's in IR, but I have a hard time thinking that push over was completely due to pilot input. Pusher perhaps. I've seen my share of bounced landings, but never one so abrupt.
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Old 22nd Jan 2014, 17:53
  #202 (permalink)  
 
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Does the Challenger have a stick pusher? That pitch down after the bounce was very severe.
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Old 22nd Jan 2014, 17:54
  #203 (permalink)  
 
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Affirmative on the stickpusher.
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Old 22nd Jan 2014, 18:42
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Seems to have generated a lot of heat at the bounce. Wonder if it's just the tires heating up or if something broke?

Also maybe a deep stall and no tail plane authority coming up off the bounce?

Right wing seems to be dropping fast in the final dive too.

Last edited by thcrozier; 22nd Jan 2014 at 19:15.
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Old 22nd Jan 2014, 19:42
  #205 (permalink)  
 
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The wind is really shaking camera 5.

It looks like it's down (nose first?) for a second or two, then the nosewheel collapses, there are sparks, and it's yanked back up, into a huge bunt/stall.
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Old 22nd Jan 2014, 21:43
  #206 (permalink)  
 
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Affirmative on the stickpusher.
Then this may be a case of death by stickpusher.
That feature should probably be attenuated or disabled below a certain radar altitude.

Last thing you need close to the ground is a big nose down input. It would be better to stall and settle in.
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Old 22nd Jan 2014, 22:32
  #207 (permalink)  
 
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Not sure if this could be related, but CG (elevator authority) has been an issue in the TEB TO overrun - see pp. 16-17
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Old 22nd Jan 2014, 22:36
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Stick Push

All I can say is WOW...what a stick push.

I've never seen one from the outside, but to me, it looks like that may be what happened.

When they made the first touchdown and the sparks flew, maybe that slowed them down so much, that when they went airborne in the bounce, the system thought it was a deep stall.

And it may have been. The right wing looks to be dropping off.

Maybe some Challenger guys here can let us know how much force it would take to over ride the pusher.

Otherwise, I would assume the only other way to over ride it would be to push the A/P disconnect? Probably happened too fast for that.
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Old 22nd Jan 2014, 23:25
  #209 (permalink)  
 
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Doesn't really look like the tail is even flying - just being carried up and over by ... momentum? thrust?

I think the thrust is coming way up at the end of Camera 2 (although the apparently increasing heat signature may just be an illusion created by the changing view angle), and the pitch angle begins to diminish rapidly as he moves off-screen to the left.

Last edited by thcrozier; 23rd Jan 2014 at 00:10.
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Old 23rd Jan 2014, 00:46
  #210 (permalink)  
 
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Just speculation - but the first hit with the nose gear is so hard, I'm wondering if it structurally failed and pushed the gear back into the aircraft, damaging other systems.
It's happened before....
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Old 23rd Jan 2014, 00:51
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Originally Posted by Machinbird View Post
Last thing you need close to the ground is a big nose down input. It would be better to stall and settle in.
That statement is making a BIG assumption about the stall that you'd experience if there were no stick pusher. If all you did was "settle in" then you'd have "certifiable natural stall characteristics" and, er, likely not have a stick pusher anyway.
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Old 23rd Jan 2014, 00:53
  #212 (permalink)  
 
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Originally Posted by barit1 View Post
Not sure if this could be related, but CG (elevator authority) has been an issue in the TEB TO overrun - see pp. 16-17
I'd be quite surprised if it were the same kind of scenario - in addition to the difficulty is being loaded outside the envelope at that point in the flight, a far forward cg would have likely presented trim issues earlier in the approach after first selecting full flaps. That they got as far as they did seems to suggest not.

Also, the aircraft appears to pitch up quite smartly just before the final pitch down, which would suggest that something was powerful enough to pitch it up.
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Old 23rd Jan 2014, 01:00
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Originally Posted by Old Boeing Driver View Post
Maybe some Challenger guys here can let us know how much force it would take to over ride the pusher.

Otherwise, I would assume the only other way to over ride it would be to push the A/P disconnect? Probably happened too fast for that.
Force - a lot. Of the order of 75lbf. It's doable, but not without effort. Which is the point, since when it fires "for real" it needs to be able to do its job.

Challenger pusher doesn't work through the AP, so that wouldn't do anything. It can be disconnected, but bear in mind it IS the designed-in stall protection system; if it's firing, it's trying to tell you something.

if they did end up low, slow and stalling at whatever altitude they reached on that 'bounce', I fear there was little left for the crew to do but pray. Which, since two of them have survived to tell the tale, maybe someone was listening to?
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Old 23rd Jan 2014, 01:10
  #214 (permalink)  
 
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@Scientist:

Any idea how much downward pitch moment high thrust would produce in landing configuration assuming the airplane was in a stalled condition? Seems to me it would be some - since the engines appear to be above CG. Pardon me in advance for any mistakes in terminology.

Last edited by thcrozier; 23rd Jan 2014 at 06:27.
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Old 23rd Jan 2014, 02:50
  #215 (permalink)  
 
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Holy s*** Batman.

What the hell was going on there???????

Surely no normal half capable experienced Pilot would push forward that hard after such a big bounce????? Well I'd hope not anyway.......

Remember the FEDEX MD11 crash in Tokyo Narita a few years ago, the crew bounced there too and pushed forward.........
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Old 23rd Jan 2014, 02:52
  #216 (permalink)  
 
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A/P Disconnect

I didn't mean to infer that the pusher worked through the A/P.

I don't know anything about Challengers, but the Gulfstream pusher could be disconnected at any time with a push of the A/P disconnect button.

It was one of the required checks.

In this landing, it doesn't look like they would have even had time to push the button, and from another poster, over riding the push manually would have been very difficult.
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Old 23rd Jan 2014, 03:26
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There is a scenario on the CRJ type whereby a bounce and subsequent movement of the thrust levers to idle can trigger the GLD (ground lift dump) whilst airborne. I think that is an unlikely issue, the largest being these guys didn't know what they were doing in the slightest.
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Old 23rd Jan 2014, 03:46
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Slowmo (camera 4 video removed):

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Old 23rd Jan 2014, 04:47
  #219 (permalink)  
 
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Questions & Assumptions

Quote:
Originally Posted by Machinbird
Last thing you need close to the ground is a big nose down input. It would be better to stall and settle in.

Originally Posted by Mad (Flt) Scientist
That statement is making a BIG assumption about the stall that you'd experience if there were no stick pusher. If all you did was "settle in" then you'd have "certifiable natural stall characteristics" and, er, likely not have a stick pusher anyway.
We are almost in agreement. Look at the assumptions I used and see if they are reasonable.
Assumption 1. The stick pusher is there to avoid a locked in stall condition.
Assumption 2. In a locked in stall, the aircraft would stay pitched up or even pitch up somewhat further relative to its flight path.
Assumption 3. Drag would rise, lift would decrease, and the aircraft would settle.
Assumption 4. Ground contact would stop the downward acceleration at a much lower velocity than would a lawn dart type earth entry thus increasing survivability. For this to be true, the stick pusher inhibition altitude would probably have to be on the order of 200 feet agl. It is still possible that a roll off could occur if controls are mishandled.

Do we really need the full 75 lbs of nose down force on the yoke in all flight conditions? Do we need a warning that the stick pusher is about to activate?
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Old 23rd Jan 2014, 06:09
  #220 (permalink)  
 
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Still guessing that after the 'bounce' they ended up high in the air, but below stall speed and with increasing thrust. The thrust seems pretty clear thanks to the IR imagery - could be wrong - but the exhaust heat signature is well formed and stable or increasing.

How that could happen is a mystery - possibly a combination of ground effect, wind shear, and automatic configuration changes?

Last edited by thcrozier; 23rd Jan 2014 at 07:11.
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