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Cargo Crash at Bagram

Old 1st May 2013, 20:18
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stacee:
I'm sure you're aware tip stall is a known phenomenon in swept wing aircraft.
Yes indeed. As that characteristic was discovered about six decades ago (see Galaxy Flyer's point on the F-100), I think you will find that aerospace engineers have come up with a variety of ways to mitigate the problems of spanwise flow. Even as far back in history as the 1970's we were taught about slats, stall fences, et al.
I imagine the extreme alpha involved in this tragic case would make any washout irrelevant.
I am not so sure.
As you are doubtless aware, washout isn't the only method used to mitigate for spanwise flow.
EDIT:
If you look at this picture
http://t0.gstatic.com/images?q=tbn:A...MC_qkyAgvf5Khp
you'll see one way that design engineers addressed that issue.
On a different scale in a fighter of a generation or two after the F-100 Galaxy Flyer pointed to, this picture shows the same basic idea at work:
http://t2.gstatic.com/images?q=tbn:A...Rcnc_P-OYxdAcQ

My less than gracious response to you suggested primary pitch control (and maybe I should have pointed specificallyl to longitudinal control authority) being a more likely source of the problem.

But we don't know. Hopefully, the FDR survived the crash.

Last edited by Lonewolf_50; 1st May 2013 at 20:24.
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Old 1st May 2013, 20:32
  #162 (permalink)  
 
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LW, writes....
"As you are doubtless aware, washout isn't the only method used to mitigate for spanwise flow."

Washout has nothing to do with mitigating spanwise flow on a swept wing, its primary function is exactly the same as in an unswept wing, I.E. delaying tip stall by reducing the AoA the tip 'sees'
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Old 1st May 2013, 20:37
  #163 (permalink)  
 
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I did ask a question earlier,but it seems to have been deleted by someone...
Most aircraft exhibit a nose-down trim change when flaps are fully lowered,which may restore some more pitch authority.....Anyone care to comment,especially those who operate 744s..?
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Old 1st May 2013, 20:46
  #164 (permalink)  
 
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Thanks, Lone Ranger, I see what I did there. Been too long, mixing stuff up in the memory again.

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Old 1st May 2013, 20:49
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Did anyone address the possibility of a trim runaway?
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Old 1st May 2013, 20:54
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Just out of curiosity.. How would these military vehicles be loaded? Would they be lashed onto a pallet with the pallet locked into position, Or loaded freely (bulk) and lashed to tie down points?

I only have experience in loading narrow body passenger aircraft. So have no idea how it works with cargo aircraft.

Sorry for a irrelevant question.

Video is both chilling and terrifying. Would make anyones blood run cold. RIP to the crew x
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Old 1st May 2013, 21:14
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A review of AF 447 will show that AOA is relevant only to flight path of aircraft. This 747 was coming down at a very steep angle so to not be stalled would have to reference to this angle. We don't have the info at this point to know the cause but landing flat with a 60 degree descent angle still puts you in a deep stall.
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Old 1st May 2013, 21:20
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Reminds all of us of that old maxim.

And it doesnt really matter why it happened or what sort of aircraft you are piloting.

If you get the nose too high, be it your fault or someone elses, a stall will follow. As sure as eggs are eggs.

Stall, spin, die.

No pilot should ever forget it- and I'm sure this crew never did.

Sometimes you are just fresh out of luck.
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Old 1st May 2013, 21:33
  #169 (permalink)  
 
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Dcoded: "Did anyone address the possibility of a trim runaway?"

Not likely. In the 747 there are two stab trim cutout switches just aft and to the right of the thrust levers. Corrective action would have been accomplished prior to the trim running away to the point that nose up trim would result in the witnessed accident.
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Old 1st May 2013, 21:36
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Someone asked who was onboard.

News from The Associated Press
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Old 1st May 2013, 21:59
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Pitch Trim runaway is one of many very unlikely possibilities, I would put money on a load shift. The boys didn't even have the opportunity to get the gear up before they were battling with the extreme nose up attitude.

The FDR will likely reveal the control input versus pitch attitude which should clear things up.

Watching this video sends chills up my spine. Prayers and condolences to the crew and their families.
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Old 1st May 2013, 22:45
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A question and speculation

In a deep stall, will the horizontal tail (not a T-tail) see such an airflow that it tends to level the aircraft or even drop the nose? Is that what I see in the video?

If that is the case, then the (presumed) loose cargo which had shifted aft at rotation could be free to shift back forward - perhaps even beyond its original planned location - and exaggerating the nose drop.
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Old 1st May 2013, 22:46
  #173 (permalink)  
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Someone asked earlier if there were any genuine aircrew left on this
forum....an outsider looking in at this juncture would think not.
I think, at this stage, all that needs to be said of this tragic accident was said in the first couple of pages, after that most of the professionals stood back and only posted thereafter to right a serious wrong. The rest of the thread consists almost entirely of speculation that ranges from highly educated to pure fantasy. MungoP's contribution is by far the most useful.
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Old 2nd May 2013, 00:43
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Can someone she light on this - would it take one of these vehicles to presumably cause this if it shifts position and therefore COG, two, more? Chain reaction where one hits the next which rips loose etc?
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Old 2nd May 2013, 00:57
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We need to hear what the CVR says and the ADC to get any real information. We know if pitched up for some reason but don't know why. Cargo shift or runaway trim could have caused it. We must wait for the black boxes to tell us.

Last edited by bubbers44; 2nd May 2013 at 00:59.
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Old 2nd May 2013, 01:03
  #176 (permalink)  
 
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Originally Posted by Stacee
but I'm sure you're aware tip stall is a known phenomenon in swept wing aircraft.
Modern swept-wing aircraft DO NOT tip-stall first. Period. They are designed that way, with washout. Your earlier point that the nose will pitch up due to tip stalling in a modern jet is simply wrong.
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Old 2nd May 2013, 01:13
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Grimmrad: "Can someone she light on this - would it take one of these vehicles to presumably cause this if it shifts position and therefore COG, two, more? Chain reaction where one hits the next which rips loose etc?"

Reportedly, there were five MRADs on the aircraft. An MRAD weighs ~25,000#. Even in a 747, this would be a considerable load shift depending on the loaded location and the distance moved.

This occurred on a military base, so the Afghans are out of the investigative picture, I'm told. Let the NTSB review the evidence and announce the cause.
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Old 2nd May 2013, 02:47
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If i were a betting man, i would consider a steeper take-off profile combined with having 1 heavy vehicle coming loose from its hold downs and breaking the other(s) free. Lack of awareness on the load ratings of the hold-down points combined with "wear and tear" reducing the available hold down points structural strength would be high on my list
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Old 2nd May 2013, 03:24
  #179 (permalink)  
 
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I'm trying to think of the simplest single reason for the loss. Does the 747 a take-off warning (like the A320) if power levers are advanced with stab trim outside of acceptable range?
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Old 2nd May 2013, 03:28
  #180 (permalink)  
 
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To auto flight:

Yes a B744 has a TO config warning system warning for an incorrect stab setting.
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