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China Southern A380 Prang LAX

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China Southern A380 Prang LAX

Old 17th Nov 2016, 06:24
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Tug approval

So it looks like the type of tug involved is significant in this chain of events? I wonder if this was their first time towing (maybe it's easier to get away with it when pushing?) a heavily laden A380 with 2 engines running with the wrong truck, and their luck ran out.
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Old 17th Nov 2016, 13:31
  #82 (permalink)  
 
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From what Jamstabbed reported, all the holes in the Swiss cheese lined up when the tractor in use had a weight insufficient to deal with the situation.

I believe, using the tractor performance figures that if shifting an A380, a tractor weight 62,500Kgs or above and good tyres, are the minimum requirements so that the aircraft cant control the operation. A GT110 is, I believe, generally 50 tonnes maximum.
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Old 17th Nov 2016, 14:36
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Given that it appears the tow bar failed, it must be difficult to blame the tug, No?
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Old 17th Nov 2016, 18:51
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... or the pilots for taxiing early. A few apologies are in order.
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Old 18th Nov 2016, 02:20
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I've pushed/towed 100's of a/c. This one's got me beat.
I cannot understand how the tow bar managed to get bent. Whether your pushing or towing the steering bypass pin must be in. The shear pins then fail if too much stress happens.
Did the tow bar simply fail?
If it did it looks like it failed when towing, with the tug reversing.
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Old 18th Nov 2016, 02:57
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APU was inop. Two outboard engines started at the gate. It was gate 159 that requires a nearly 180 degree turn during the pushback onto taxiway C.
It's only about a 30 turn. The 380s are pushed into C, tail east, and then towed forward until roughly abeam 156 for start. They are not permitted beyond C10 whilst on C.
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Old 18th Nov 2016, 16:26
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I was told that it was tail west(150 degree turn) which is what I have done in a 777 from that gate. Maybe a pushback direction error was made for whatever reason(possibly by the tug driver used to smaller aircraft on the gate going tail west) which might explain why there was a subsequent tow forward required with a tight turn back toward the gate in order to pushback once again in the proper direction. Or maybe the story told to me was in error.
But a plausible scenario.
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Old 18th Nov 2016, 16:36
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Towbar failure

If the towbar failure was the trigger for the accident then it must have been in compression, ie pushing on both ends... perhaps not entirely along the axis.

After that the plane must have moved forwards to hit the tug. Also the fact that the nosewheel is pointing straight ahead seems important
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Old 18th Nov 2016, 18:36
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... perhaps not entirely along the axis.
Surely the load on a towbar has to be along its axis - unless the towbar comes into contact with something else!
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Old 18th Nov 2016, 22:46
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It seems to me that if the aircraft was being towed around a curve, the engine thrust (or just the inertia of the aircraft if the tug were slowing) would tend to push the back end of the tug (or the one hooked to the towbar) to the outside of the curve. If the tug were too light and the rear tires didn't have enough traction to resist this force, the tug could spin partway around, in effect jackknifing. At some point in that sequence, the side of the towbar would presumably come up against something it wasn't supposed to.
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Old 18th Nov 2016, 23:40
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Surely the load on a towbar has to be along its axis - unless the towbar comes into contact with something else!
Normally... but say the wrong bypass / shear pins were used... then during turns there could be enough torque on the tow bar to break it.
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Old 18th Nov 2016, 23:46
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...and assuming the aircraft's steering pin was inserted.

On that type of tow bar, does part of the bar pivot if shear pin(s) shear?

(EDIT) Sorry.. crosspost (with previous poster)
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Old 19th Nov 2016, 00:08
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Originally Posted by peekay4
Normally... but say the wrong bypass / shear pins were used... then during turns there could be enough torque on the tow bar to break it.
Is it possible that the shear pins broke as designed and then the tow bar bent a few seconds later as the incident continued on with the nosegear jamming the bar against the towtruck?
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Old 19th Nov 2016, 00:50
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There were certainly some unsual forces at play here. The angle of the tug, the flat tyre, the tilted tug cab (cabin) ...

Even if the driver kept his foot on the accelerator after the shear pins broke, why would the tug end up at that kind of angle?
The tow bar isn't touching the cab of the tug, so I assume the tyre of the aircraft did the damage to the cab: I assume there would be no twisting forces generated by the bar, because the (tug) end of the bar is usually pivoting.

I've seen the results of pushback/tow incidents, but fortunately none first hand. Some attributed to aggressive tug driving, forgotten steering pins, pilots putting on the park brake without being told, pilots not putting on the park brake (even though they said they had), tug driver heart attacks, tug drivers falling asleep, faulty tug steering ....
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Old 19th Nov 2016, 02:30
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Looking at the photos and hearing some of the comments I'd say this a/c was definitely being pushed around a corner.
I'd say the driver got the turn all wrong and ended up stopping the tug almost under the Captain at 90 degrees to the tow bar with the a/c nose wheel pretty much pointing straight ahead. Probably not much of an issue with the correct tug but as has already been pointed out this tug was not rated to push the A380.
If by this time, a couple of engines were already started, and because the tug was too light and at an angle, the a/c moved forward under its own power. The tug would've been unable to stop it. This would also explain to front tyre being rolled under and, as the front right of the tug contacted to tow bar, would explain the bend in the bar also.
All in all a rectum tightening experience.
The lesson here; don't use an under rated tug.
Just my thoughts, happy to be corrected.
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Old 23rd Nov 2016, 19:05
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... or the pilots for taxiing early. A few apologies are in order.
Still nothing? It figures!
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Old 24th Nov 2016, 07:36
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Purely a hypothesis ...

During pushback/tow, the tug lost traction and with wheels spinning the front of the cab hit the towbar (pivot on the pin connecting tug to towbar) and caused the bar to bend as under tension during operations. Bar bent in a similar way to standing on an empty drink can and touching the side of the can, lateral push force on its own probably wouldn't cause bar to bend.

Guessing the aircraft moving forward and the bent bar didn't create enough force for shear pins to break (still connected to aircraft) and as the bent bar allowed the aircraft to move forward over the tug, friction from tug tyres sideways meant the tug was trying to 'roll' so the suspension compressed and the opposite side of cab moves up (possibly in conjunction with the aircraft pushing against cab).

Others have said tug (possible max weight 54T from earlier link?) was not up to the job, could this be the route cause and knock on effects? Loss of traction due underweight tug, wheels spin and tug moves sideways, tug hits bar and bar bends, and aircraft forward momentum continues to bend bar and aircraft hits tug.

Interesting that Menzies bar used and Swissport tug. Who handles China Southern in LAX? Was the equipment borrowed following break down and not really fit for purpose?
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