Accidents and Close Calls Discussion on accidents, close calls, and other unplanned aviation events, so we can learn from them, and be better pilots ourselves.

Cargo Crash at Bagram

Old 3rd May 2013, 14:26
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Non deployment of leading edge flap won't cause pitch up. What would happen is without leading edge flap the calculated Vr would be low for the lift generated so the aircraft may still lift off in the ground effect but would not be able to climb out of it. The pilot would not be able to raise the nose as speed will fall. Similar accident has happened before. But the nose would not be high. Cargo shift appears more likely.
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Old 3rd May 2013, 14:38
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RG, by the time of the steep right wing down, the outcome was probably no longer in doubt due to lack of altitude for recovery. (EDIT: sorry, TorqueTonight already made that point. )

(IIRC, BOAC observed a few pages back that with internal cargo moving about it's a whole different problem).

You may find the NASA paper hval linked to of interest, as it addresses stability and internal CG shift when there is a flight control malfunction. Not directly related, but maybe linked to your question in terms of influence on lateral stability.

Last edited by Lonewolf_50; 3rd May 2013 at 14:41.
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Old 3rd May 2013, 14:51
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Thanks for the link, Lonewolf, I'll take a look.
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Old 3rd May 2013, 15:12
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and More questions..

Just a thought I'm throwing out.

During "normal" flight, the combination Horizontal Stabilizer and Elevator create downward lift. I previously assumed there was a load shift, of a significant enough moment, to prevent the pilot from being able to lower the nose, utilizing both full elevator and stabilizer trim ( not enough lift ). And this occurred while the tail had airflow over it. I am also assuming the horizontal stabilizer reached a stall condition prior to the majority of the wing ( approaching the apogee ), and maybe was developing NO ( vertical) lift.
My question that I'm throwing out is, if the C.G was so far aft, Why didn't we see a tail slide in the video?. Or possibly a flat spin?.
What I saw in the video, was what I believe to be a "normal" high AOA stall, with the aircraft going through all the roll, yaw, and pitch changes that one would expect to see.....followed by the beginning of a "normal" recovery. This is how we expect an aircraft to react, assuming the C.G. is within limits.
I think we are all trying to make "sense" of what happened along with this video. It is hard to just let this go. Excuse my poor wording.
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Old 3rd May 2013, 15:35
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First step,

If an aircraft that is in equilibrium has the CG moved rearward a nose up pitching moment will result. As long as the CG is in such a position that the aircraft still has positive static stability then when the airspeed decays to the point where the main wing stalls and loses lift, then the nose will drop.

The aerodynamic centre of the entire aircraft, the neutral point, is the point at which the pitching moment does not vary with the pitch incidence. The distance between the CG and the neutral point is the static margin. If this is positive, ie the CG is ahead of the neutral point, the aircraft has positive static longitudinal stability, and a disturbance in pitch will cause a corrective pitching moment.

With zero static margin there is no corrective pitching moment and if the CG moved behind the neutral point, negative static margin, then the aircraft would be unstable and a disturbance in pitch would result in an exacerbating pitching moment, and the aircraft would try to flip around and fly backwards, like throwing a dart with the feathered end first.

So it would seem that the aircraft had a rearward CG shift to cause a nose up pitching moment that could not be countered with the pitch authority available, however the CG was still ahead of the neutral point and still had positive static stability hence the aircraft dropping the nose at the stall and not going in tail first.

This is how we expect an aircraft to react, assuming the C.G. is within limits.
Not exactly. For an aircraft to be controllable and maintain a minimum level of stability the aft CG limit will be some way forward of the neutral point. So an aircraft might be out of CG limits, CG behind the aft limit but still ahead of the neutral point, and therefore still have some static margin and positive (albeit reduced) stability. Such a CG would however result in an incorrect stab trim setting and insufficient pitch authority to control the attitude. Pitch authority/trim and stability are two separate but related issues, and you can lose pitch authority before losing longitudinal stability.

Last edited by Torque Tonight; 3rd May 2013 at 15:50.
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Old 3rd May 2013, 15:37
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Hallelujah
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Old 3rd May 2013, 16:13
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Please forgive this probably ignorant question, but if the load shifted rearwards on rotation causing the CoG to shift back, surely when the aircraft stalled and pitched down the load was likely to shift forwards again? If this is correct, would there not be some sign of this on the video?
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Old 3rd May 2013, 16:16
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There was some speculation and confusion a few posts back about the cargo's destination and the flight stages involved in getting it there.

Firstly, its not actually relevant really, but just to add some clarity, I don't see anything unusual about the routing for this flight. Bear in mind National are under no obligation to discuss anything with anybody about the cargo's ultimate destination, which was probably not DWC! Dubai was where it was going next, but quite likely only for a tech stop with crew rest. Where it was going after that is quite frankly nobody's business and we cant expect it to be disclosed.

Quite probably, it was eventually destined to go to a US Military location back on the US mainland. I can already hear the armchair navigators spinning their plastic desk globes around and itching to shout me down on this point, but there's a few detailed things to consider:

* These are professional civilian flight crews and they don't particularly like to crew rest in war zones, so it is quite normal to get in, load up and get out, then crew rest in nearby civilised areas like UAE, or wherever the remaining FDP/Fuel will let them get to.

* These guys operate hot and high at close to max load, so the sectors do tend to be a bit short, add to that a positioning flight into the territory, loading, flight across territory due to fuel limitations and you can see how your FDP is running low already, so off to next nearest familiar civilised tech stop location.

* These flights are not scheduled, so there are no RPL's, they all need to be planned on a sector by sector basis, there are no "blanket permits" for these territories and every territory overflown must be individually contacted to obtain overflight or landing permits. Add into the mix a "diplomatic cargo" such as this one and before you know it every one of the regions in that area will start to demand additional details/time and in many cases can be quite obstructive - for example: where do you need to overfly to get to Dubai? Iran or Pakistan. Good luck trying to organise THAT carrying a military cargo from a US air base, irrespective of whether it is a civilian carrier! It's not impossible but its time consuming and there's every chance the original plan gets re-written several times, maybe even going the long-way-round. Once you get to DWC you're then looking at onward routes involving Iraq, Israel or Egypt. Your sectors back to the US won't be predictable until you are past the Med.

The point I am trying to make is that flights like this in these areas are operationally challenging at every imaginable level and you can't just draw a line between Afghanistan and Dubai and then just file to the closest ATS routes.

I reiterate that whatever the actual operational details of this flight's particular routing were, it is irrelevant to the unfortunate incident that occurred. I just wanted to clarify that there is nothing unusual about the routing scenario that has been mentioned by others.
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Old 3rd May 2013, 16:33
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Raikum, when and where would you expect to see that evidence?

Once the plane hits the ground, it's all obscured by a fireball, smoke, and flame, or viewing other things, until that clips comes to an end.

The video extract wasn't being deliberately taken as a documentary or even directly at the aircraft. It's a bit of a luck, security truck being in the right place at the right time. As noted numerous times previously, viewing angle, perspective, movement of vehicle, and limitations from looking through thick glass (not to mention pixelation) all conspire to make it a brief and imperfect (and partial) glimpse of a mishap.

To directly answer your question: from the outside, it is a bit much to ask an observer to discern that an internal (and to him invisible) load shift forward would have directly caused a pitch down before ground impact.

What the NTSB investigation may be able to uncover, with hopefully intact FDR and CVR evidence, may provide some answers to your questions in due course.

Last edited by Lonewolf_50; 3rd May 2013 at 16:36.
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Old 3rd May 2013, 16:49
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parking brake?

I assume the vehicles have parking brakes? Transmissions that can be parked/set into low gear? I wouldn't simply assume that cargo shift is the cause. A pallet on coasters, would be thinkable. But that's not the case here.

Furthermore - once the plane was in a 90 bank, nothing would have prevented rear loading from rotating the empennage rapidly downward. That didn't happen.

Third - probably this problem was present at rotation since the wheels were down the whole time. Vehicles crashing rearward at or before rotation would have immediately told the crew to abandon any hope of a successful departure.

I'm thinking that this points to a problem with the airplane itself.
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Old 3rd May 2013, 16:59
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Does the 400F have tail fuel tanks?
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Old 3rd May 2013, 16:59
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At 90 degrees bank, the vertical stabilizer would be the most influential aerodynamic force on the pitch attitude of the fuselage relative to the horizon. No matter how far aft the CG, it is still way ahead of the center of lift of the fin. The nose is going to fall, no matter what.
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Old 3rd May 2013, 17:16
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DeSitter: Sorry sir but what? Parking brakes? You seriously think they would secure a battle-worn overweight troop carrier in the cargo hold of a vehicle that moves in three dimensions and secure it with a parking brake? The parking brake would be next to useless even if the vehicle was strapped in and the strapping let go. The vehicles would be parked in gear as a precautionary starting point, but that will only keep it still while the aircraft is stationary.

You don't need such a vastly out of balance rear loading condition that an aircraft can only physically exist in a vertical condition in order for the flight controls to be ineffective. if that were the case it would have crashed a lot sooner or been sat looking at the sky on the loading ramp!

The video clearly shows the aircraft was airborne and flying albeit with high alpha and limited longitudinal control, so we can assume that any load shift, if it occurred, put the CG somewhere behind the aft limit. That doesn't mean all the cargo mass was located at the tail cone!

And no it does not automatically mean that if the cargo moved aft it would necessarily move back forward again, I can see your thinking that if its broken free it can go anywhere, but there's 50-70 straps holding these things in, they shouldn't move at all, but if they so there's all sorts of factors involved that could resist further movement.

Balance is a variable condition. "In balance" is quite a narrow spectrum. "Out of balance" is infinite, but realistically for this aircraft to reach the height it did it must have been somewhere in the early stages of being out of balance... in which case it would be possible for the aircraft to manoeuvre nose down as seen in the video.
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Old 3rd May 2013, 17:48
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You guys need to see the video.

Hight pitch angle. Clear the pilot was working the rudders, veers left, then right wing slalls. Instead of flipping over right, the plane goes over and recovers wings level. This is important.

Best I can tell this is classic departure stall and start of a recovery with the caveat that the only way they could have gotten the wings flying again, was by the addition of power.

That belies that the aircraft departed under derate power, when the wing stalled, training took over, they firewalled it, got wings level, not enough altitude and airspeed to recover, pancake landing.

What causes the stall, high AOA/Pitch might have been a loadshift, like Dallas an A/S malfunction with pilots flying the numbers and not cross checking visuals. Ponder also that the gear was still down, which belies a possible flap/slat retraction instead of a gear retraction, easily putting the aircraft into a stall if departing high, hot, heavy, and SOP there as fast climb to mitigate fire from the ground.

What ever the case, I can almost guarantee that power was applied AFTER the wing stall.

Good point that radio call under those conditions would be last thing anyone would do, but ponder they might have 'worked' this problem for a while that maybe the copilot made the call.

Last edited by Teldorserious; 3rd May 2013 at 17:49.
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Old 3rd May 2013, 17:52
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Was looking at a pic of how the Vehs were secured..

Certainly a lot of anchoring points.
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Old 3rd May 2013, 18:22
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tail fuel tanks

Does the 400F have tail fuel tanks?

Diamond,

No.
It being a BCF means it used to have tail tanks while still a passenger aircraft, and they would physically still be there, but during the conversion to freighter they would have been deactivated.
F and ERF models don't have 'm to begin with.
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Old 3rd May 2013, 18:23
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Clear Prop,

Are you really asking me to believe than any vehicle of any sort, north of a bicycle, doesn't have a method for preventing it from rolling when parked? And unless the carrier is in free-fall, that method will not allow the vehicle to roll backward under gentle acceleration, which is the physics equivalent of parking on a hill.
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Old 3rd May 2013, 18:33
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deSitter, from the pictures of example strapping/tie down of MRAPs that some have provided in this thread, I think some of the estimates of load shift are pallet slip / slide / /malfunction (and straps snapping??) not a rolling of wheels.

Does that make sense?

Last edited by Lonewolf_50; 3rd May 2013 at 18:35.
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Old 3rd May 2013, 18:35
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on post 320 by hval on the loaded vehicles picture: Anyone knows why there are wood boards under the front axle of the vehicle? (there seem also to be mid vehicle and to the back axle).

Is the weight of the vehicle supported by the wood instead of the suspension? The tyres seem to be 'flat' but maybe they are deflated and not realy support the weight of the vehicle?

The straps seem to be tensioned to push the vehicle 'down' against the wood. Is that the case?

If the above is the case, then all the sophistication and safeguards of the loading system depends on those wood boards. 1-2 less boards and the vehicle weight is supported by the front straps only (straps are only good in tension)

Its JUST a question IF anyone knows, I'm no pilot or loader just curious.

thanks

Last edited by Dimitris; 3rd May 2013 at 18:36. Reason: grammar
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Old 3rd May 2013, 18:35
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Not really, when there are 5 vehicles totaling likely 100,000 lbs. A pallet, unless filled with lead bars, would be a delta on this load.
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