Cargo Crash at Bagram
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Original post by hval earlier in this topic, seems fitting considering recent news ... image on the post is of the MRAP properly strapped in a 747-400.
http://www.pprune.org/rumours-news/5...ml#post7824288
http://www.pprune.org/rumours-news/5...ml#post7824288
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From a 30 year freight Dog:
Cargo straps, as far as I know, have no regular checks, like a fuel control unit may have. They are inspected on a daily basis as used, much like a cargo container. Looking for tears, abrasions, rips, cuts...................
I have very high regard and respect for each of our loadmasters. Not that I don't go down and have a look see now and then, but I have never had a real problem with our loadmasters capabilities and performance.
Nylon Straps stretch, lets say that 100 pounds of tension was put on each strap.... and they relaxed to 50 pounds of tension. They still had a positive tension, forward, aft, up and down. even if the straps slacked off to neutral, the locking mechanisms would hold fast. If the load shifted,it might move a little whichever way, but the movement would not be shocking to the floor fittings due to the nylon stretching. Shock absorbers.
My questions are, the tie down loops on the vehicles, Were the edges sharp/ragged? Who did the cargo mod to the aircraft? Did they install the cargo restraint system properly? Was it previously over stressed somehow ?
I know from personal experience, that even during a tech stop,at minimum, the loadmaster, and one of the copilots take a little walk down stairs........ for a look see! Especially, on the SPECIAL LOADS.
This accident has made the cargo carriers second guess their procedures and SOP's to the NNNNNNth degree.
As sad as this is; hopefully we can learn something positive from this tragedy.
Cargo straps, as far as I know, have no regular checks, like a fuel control unit may have. They are inspected on a daily basis as used, much like a cargo container. Looking for tears, abrasions, rips, cuts...................
I have very high regard and respect for each of our loadmasters. Not that I don't go down and have a look see now and then, but I have never had a real problem with our loadmasters capabilities and performance.
Nylon Straps stretch, lets say that 100 pounds of tension was put on each strap.... and they relaxed to 50 pounds of tension. They still had a positive tension, forward, aft, up and down. even if the straps slacked off to neutral, the locking mechanisms would hold fast. If the load shifted,it might move a little whichever way, but the movement would not be shocking to the floor fittings due to the nylon stretching. Shock absorbers.
My questions are, the tie down loops on the vehicles, Were the edges sharp/ragged? Who did the cargo mod to the aircraft? Did they install the cargo restraint system properly? Was it previously over stressed somehow ?
I know from personal experience, that even during a tech stop,at minimum, the loadmaster, and one of the copilots take a little walk down stairs........ for a look see! Especially, on the SPECIAL LOADS.
This accident has made the cargo carriers second guess their procedures and SOP's to the NNNNNNth degree.
As sad as this is; hopefully we can learn something positive from this tragedy.
It's been many years since I've delt with loads in aircraft, but I regularly travel with heavy and potentially shifting loads with vehicles in offroad areas of the Sahara. We use the scaled-down version of the same nylon straps used for securing loads in aviation. With the constant vibration and shaking, no matter how tight one pulls the straps, within a few hours they will develop a slack due to the inherent flexibility of the material and the constant microscopic movement of the load. At some point, the slack will be big enough to permit a visibe shift of whatever is secured. These straps need constant tightening, they are checked every time the vehicle stops (naturally load shift conseqences are not as disasterous as in aviation, but in the worst case can cause a vehicle to overturn).
The accident sequence could have been initiated by load shift due to one or more loose straps, the failure of an attachment point, or a failure of a strap itself. Once the initial movement occurred, the rest was just domino effect. Hopefully a more detailed report will shed more light on these possibilities.
The accident sequence could have been initiated by load shift due to one or more loose straps, the failure of an attachment point, or a failure of a strap itself. Once the initial movement occurred, the rest was just domino effect. Hopefully a more detailed report will shed more light on these possibilities.
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Don't know about other airlines but the one I work has following rules:
Straps are allowed to be used max 5 years - manufacturing month and year is printed on them.
Maximum weights are;
1300Kg upwards (3g) and
2600Kg forward and backward (1.5g)
Presume the vehicle + ULD + other loading material weighs 16tons it would need minimum 27 straps to hold it in place; 7 for forward forces + 7 for backward forces + 13 for upward forces.
Straps are allowed to be used max 5 years - manufacturing month and year is printed on them.
Maximum weights are;
1300Kg upwards (3g) and
2600Kg forward and backward (1.5g)
Presume the vehicle + ULD + other loading material weighs 16tons it would need minimum 27 straps to hold it in place; 7 for forward forces + 7 for backward forces + 13 for upward forces.
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Willit Run
Agree with your thoughts there. My belief is that Shackles should have been used on those Loops and the straps then secured to the Shackles. This would eliminate any possible Fraying/Slicing of the straps.
Am not claiming that this was the cause, just an observation.
My questions are, the tie down loops on the vehicles, Were the edges sharp/ragged?
Am not claiming that this was the cause, just an observation.
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Another aspect affecting strap failure is the angle at which they are attached relative to the load-path.
If they had the vehicles close together to achieve satisfactory loading (not unreasonable assumption with heavy cargo like this) the angles to tiedown points could well be considerable and that seriously compromises the load at which they fail.
If they had the vehicles close together to achieve satisfactory loading (not unreasonable assumption with heavy cargo like this) the angles to tiedown points could well be considerable and that seriously compromises the load at which they fail.
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On the road.
Last edited by crippen; 6th Jun 2013 at 22:15.
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Another aspect affecting strap failure is the angle at which they are attached relative to the load-path.
So When "d" becomes very small with respect to "w", very small changes in Force (the force produced as acceleration acts on the restrained mass) can result in extremely large changes in the strap tension. Either the strap or the floor anchor points could fail and it might only take one to start a domino effect that causes a complete failure.
Last edited by areobat; 7th Jun 2013 at 00:19.
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Preliminary report... huh what? Disappointing no news organization provided any link to the document
Jopu, out of curiosity. Is the reason for using relatively low WLL (Working Load Limit) straps limited to the maximum load of the aircraft's fixing points? If that's the case it will explain the need for such a large number of straps. Given a choice I would have prefered fewer with higher WLL.
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I seem to remember in the Air Force I was in many years ago, there was a "metal on metal" rule regarding vehicle restraint. Don't they use chains and tensioners any more?
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It seems that the wood is only held in position by the weight of the vehicle. This is completely unsatisfactory in an aircraft. If the wood moves, the restraint becomes slack enough for sudden forces to allow vehicle momentum prior to restrain action. Restraint systems should ensure zero movement of all components.
If the wood was individually restrained to the aircraft or to the vehicle, there would be less chance for the restraint system to become slack.
During my C130A days I took great responsibility to check load restraint, arriving at the aircraft up to 60 minutes before the loadmaster and rest of my crew. I always assumed there would be a difficult to see problem, but there never was. I would not have accepted wood support that itself was not restrained.
It is starting to look like dunnage movement was the initial problem. They probably do not really want to explore this possibility because it is an approved restraint system.
If the wood was individually restrained to the aircraft or to the vehicle, there would be less chance for the restraint system to become slack.
During my C130A days I took great responsibility to check load restraint, arriving at the aircraft up to 60 minutes before the loadmaster and rest of my crew. I always assumed there would be a difficult to see problem, but there never was. I would not have accepted wood support that itself was not restrained.
It is starting to look like dunnage movement was the initial problem. They probably do not really want to explore this possibility because it is an approved restraint system.
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autoflight:
That would be rather corrupt on the part of the investigators, wouldn't it?
It is starting to look like dunnage movement was the initial problem. They probably do not really want to explore this possibility because it is an approved restraint system.
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On the Cross Channel Car ferry of some 50 years ago, we carried two (large) or three (ordinary sized) cars on each of up to six round trips per day, possibly up to 36 cars in my working day. Each of the cars was clamped to the floor of the Bristol Freighter, which I think had channels for the wheels. Each of the wheels was clamped with chains around each wheel to two anchor points per wheel, using tensioners. I do not recall if dunnage was ever required or used.
Turnarounds on each flight were quick. The Chief Pilot said that we " had split second timing", with three cars off and three cars on in a very few minutes for the 20 minute flights, each way.
Of course the weight of the loads on the Bagram 747 were different. But in principle, some of the factors would have been similar.
Later, when carrying hard loads in a Britannia, perhaps oil barrels or heavy metal, we would have a false, plywood floor, to protect our more valuable, "passenger" floor. This would tend to distribute the weight to some extent
Of course, others may know the tie-down strengths applicable
Turnarounds on each flight were quick. The Chief Pilot said that we " had split second timing", with three cars off and three cars on in a very few minutes for the 20 minute flights, each way.
Of course the weight of the loads on the Bagram 747 were different. But in principle, some of the factors would have been similar.
Later, when carrying hard loads in a Britannia, perhaps oil barrels or heavy metal, we would have a false, plywood floor, to protect our more valuable, "passenger" floor. This would tend to distribute the weight to some extent
Of course, others may know the tie-down strengths applicable
Last edited by Linktrained; 9th Jun 2013 at 14:50.
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Can I repeat my post 509 without getting slapped down by experts this time.....and ask again what sort of wood are we talking about ?
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arc tan cos - heck, dem are loadies, not einsteinwannabes...
Standard gear is the strap with double-stud fitting, rated at 5000 lbs ( 2250 kg ). So if you want to secure for let's say 3g upwards and you got a piece of 15000 kgs: 15000 multiply by 3 gives 45000, divide by 2250 makes 20 straps evenly spaced over the piece and evenly clipped to the seat tracks. Upwards means upwards . Too much deviation from the direction u wanna secure it for will of course lower the capabilities of that particular strap considerably. Means you will need even more straps to compensate. With loads comprising of lots of floating units ( i.e. not secured by the locks available) securing the load can take a hell of a lot longer than the loading itself...
Standard gear is the strap with double-stud fitting, rated at 5000 lbs ( 2250 kg ). So if you want to secure for let's say 3g upwards and you got a piece of 15000 kgs: 15000 multiply by 3 gives 45000, divide by 2250 makes 20 straps evenly spaced over the piece and evenly clipped to the seat tracks. Upwards means upwards . Too much deviation from the direction u wanna secure it for will of course lower the capabilities of that particular strap considerably. Means you will need even more straps to compensate. With loads comprising of lots of floating units ( i.e. not secured by the locks available) securing the load can take a hell of a lot longer than the loading itself...