Intruder
Chains are used directly on many (inc. McDDouglas/Boeing) cargo aircraft, by design. http://s27.postimg.org/i7ky0py6b/ers.jpg Are you suggesting the 747 freighter has specific limitations on the use of chains on its floor tie down rings? Seems odd. |
Civil transport aircraft?
Military aircraft are designed to significantly different specifications and requirements. The 747 does not have any tiedown rings in the cargo floor. From our W&B manual which covers the 747 and 767: The use of chains or other rigid devices for tie-down onto Company aircraft floor seat tracks is prohibited. . . . The use of chains for tiedowns is prohibited on Company aircraft. . . . The use of chains for tiedowns is prohibited on Company aircraft. . . . The use of chains for tiedowns is prohibited on Company aircraft. |
Ok, so why is that ?
|
Lets all take a deep breath.. The 747 is not a C5 or a C17… We do not use chains to tie cargo to the floor. We use straps.. And lots of them. Everyone keeps posting pictures of cargo on military planes using chains to secure cargo. We CAN NOT use chains. In 24 years as a 747 loadmaster I have moved all kinds of large cargo. From a 150000 pound generator on two 20 foot pallets. To a 30000 pound role of cable..I always do the same thing. Put locks up FWD and AFT of the pallet and then strap it like we have no locks. The fact of the matter is 1000+ MATV's have moved from CHS to OAI on 747 200. 300 and 400's. With out issue. National did something different that day. Those buckle straps suck.. They Never should have be used on a heavy load..
|
My guess would be that the chains are stronger than the fixings so when they're tightened up the fixings give and eventually break under stress. But I'd guess that manual comes from a passenger aircraft rather than a cargo aircraft and has a different design?
Edit: Just read your last comment about 747 cargo craft. |
Could fatigue be a significant factor in the crash. The crew were on duty for 21 hrs prior to the accident.
|
If the vehicle smashed the THS jackscrew, any pitch control movements by the crew may have been moot. ... :{
. |
If the vehicle smashed the THS jackscrew, any pitch control movements by the crew may have been moot. ... |
The following extract from the NTSB report is the beginning of a conversation on the flight deck, concerning MATV's which were found "loose" in the aircraft.
TIME and INTRA - COCKPIT COMMUNICATION TIME and AIR - GROUND COMMUNICATION SOURCE CONTENT SOURCE DCA13MA081 CVR Factual Report - Page 11 of 29 08:51:09 [start of recording] 09:57:23 [Start of Transcript] 09:57:33 CAM - 2 there’s your trouble Brad. 09:57:35 CAM - 1 what is it? 09:57:37 CAM - 1 what the # was that from? 09:57:39 CAM - 2 one of those # straps is busted. 09:57:42 CAM - 3 * * tire. 09:57:44 CAM - 1 no no, I know that... * no I know, but.... 09:57:45 CAM - 2 give you one guess what was right there. 09:57:49 CAM - 1 what was right where? 09:57:49 CAM - 2 right here. 09:57:50 CAM - 1 a knot? 09:57:51 CAM - 2 uh huh. 09:57:52 CAM - 1 that was the one right at the door? 09:57:54 CAM - 2 no... this was at.... * *. 09:57:56 CAM - 1 so you ( go on/goin ) puttin more straps (on #)? 09:57:59 CAM - 2 (well) it just shifted (apparently/barely). 09:58:01 CAM - 3 there was a bunch of them first... that first (truck). 09:58:02 CAM - 1 did it move? .... # moved? 09:58:04 CAM - 2 yes. just tightened up on the straps. 09:58:06 CAM - 2 the truck? 09:58:06 CAM - 3 * like.... tightened those straps up uh, quite a bit, on the first one. 09:58:13 CAM - 2 you know how that...well you go look at the.... went and looked at them now... all the ones * they had a bunch like this, to keep them from movin backwards...a bunch like this * * movin forward? all the ones that were keepin em from m ovin backwards were all # loose. 09:58:28 CAM - 3 what the # do you think' s gonna happen when you # slam it on th e r unway and slam on the # brakes and don't use reverse... [ said in a joking manner] 09:58:35 CAM - 1 [sound of laughter] 09:58:36 CAM - 2 there ain't nothin you coulda done about that. 09:58:37 CAM - 3 * * I'm putting it on the # # board I'm gettin off this plane, I'm scared. [ said in a joking manner ] 09:58:43 CAM - ? * *. 09:58:46 CAM - 1 thow that out man, that’s evidence. * @ [the loadmaster] don't want that hangin around either. 09:58:50 CAM - ? no. 09:58:53 CAM - 1 I hope instead of * rather than just replacing that ( strap ) I hope he's beefing the straps up more. 09:58:59 CAM - ? just on that one spot. 09:59:00 CAM - 2 yeah. 09:59:02 CAM - ? all the rest of them are fine. 09:59:06 CAM - 2 he's cinching them all down. 10:14:49 CAM [ break in transcript] 10:14:57 CAM - 1 what’s up, dude? 10:15:01 CAM - 2 did you throw that other strap away? 0:15:04 CAM - 1 what did you - did you put a couple more on? 10:15:11 CAM - 1 how far did it move.... a couple of inches? 10:15:13 CAM - 4 yeah, they just moved a couple inches... cause you k now, its nylon ya know, so. 10:15:20 CAM - 2 (you throw some) numbers (in here)? 10:15:21 CAM - 1 that’s scare - ... that's # scary - 10:15:24 CAM - 1 without a lock (for those big heavy things / ** anything) man I don't like that. 10:15:27 CAM - 1 I saw that, I was like # , I never heard of such a thing. 10:15:30 CAM - ? * I'd be kinda interested ta ... wish I could put a camera down there and watch it..... 10:15:36 CAM - 2 (you'd probably) # yourself. 10:15:37 CAM - 1 right. 10:15:37 CAM - ? see what they do. 10:15:39 CAM - 1 those things are so # heavy you'd think though that they probably wouldn't hardly move no matter what. 10:15:42 CAM - 4 they always move.... everything moves. If it’s not strapped - 10:15 :46 CAM - 1 no no - I - 10:15:48 CAM - 4 it'll roll on them things [makes a 'motorized' sound ] 10:15:51 CAM - 1 [sound of laughter] |
Strap Fatigue
Once overloaded, it's time to retire the strap.
Unlike aluminum parts where a crack propagation can be seen and analysed, I don't know what could be found by examining a failed strap. This will be a new area for the NTSB to explore. If these straps had been used over dozens of flights with some overstresses, they would not be at full new strength. Climbers retire equipment after one or more falls. The landing seems to have damaged some straps, likely those restraining forward movement. Then we have a failure in straps restraining backward movement. Was there an elastic rebound on landing that overstressed the straps restraining backward movement:confused: Or did the straps hold while the anchor points gave way? |
RatherBe:
From the photos I have seen in the linked NTSB report, the heavy equipment was tied down to pallets using chains. If you look through the documents you'll find them. So where would the straps come into the equation? Are the pallets then strapped to the fuselage of the aircraft? |
Summary
A National Air Cargo Group (MUA) 747-400 Boeing Converted Freighter (BCF) [RT075/N949CA] crashed shortly after takeoff from Bagram Air Force Base (OAI), Afghanistan on April 29, 2013. There were no survivors among the 7 crew members onboard. The event is under investigation by the Afghanistan Ministry of Civil Aviation and Tourism (MOCAT) with assistance from the National Transportation Safety Board (NTSB), the Federal Aviation Administration (FAA), National Air Cargo and Boeing. The Flight Data Recorder (FDR) data were provided to Boeing for analysis. The FDR data show a normal takeoff was performed from OAI, but just after lift-off, the FDR recording stopped with the airplane approximately 33 feet abov e the ground. Video of the airplane just after lift- off at a low altitude over the runway shows an extremely high pitch attitude before experiencing a stall and impacting the ground at a nose-down pitch attitude. The airplane was carrying five Mine Resistant Ambush Protected (MRAP) vehicles, each weighing at least 28,000 pounds. The available FDR data, Cockpit Voice Recorder (CVR) data, and physical evidence (video, airplane component analysis), withadditional support from simulation analysis, suggest th at around lift-off, at least one MRAP (aft-most)b roke loose of its restraints, shifted aft and damage d the FDR/CVR before penetrating the aft pressure bulkhead. The MRAP’s aft movement was determined to have compromised at least Hydraulic Systems #1 and #2 and may have contacted the stabilizer jackscrew assembly. Simulation analysis indicated that an incremental airplane-nose-up stabilizer deflection (stabilizer would have likely deflected Leading Edge[LE] down if it were free to rotate) of 5 units or more could have produced the observed airplane motion. If the stabilizer jackscrew actuator had been displaced downward by the MRAP during takeoff, continued safe flight and landing most likely would not have been possible. An investigation of the stabilizer jackscrew occurred on the 15 th of January 2014. Results of the examination were inconclusive as to whether displacement of the stabilizer jackscrew from its fuselage mount occurred prior to impact. |
In post number 4 of this lengthy thread, "load shift was reported" and that line of inquiry seems to have been confirmed by the investigators. In between, some interesting topics regarding flying and hauling freight came to light as discussion progressed.
RG, that excerpt is grim reading. |
Interesting, so civil cargo aircraft don't have tie downs you can use chains with.
Are they designed instead all around pallets with some kind of longitudinal mechanical locks into the floor? As above, do the straps augment these? EDIT - this photo suggests straps augment the pallet restraint. http://s1150.photobucket.com/user/Mt...2ba8.jpeg.html |
JFZ90 wrote:
That said, the way the MRAPs were chained to the pallet on the bagram loading photos seemed to have quite a low number of chains at orientations not suggesting much longitudinal restraint for such a heavy vehicle compared to some typical mil tie down schemes I've seen. |
Interesting, so civil cargo aircraft don't have tie downs you can use chains with. Are they designed instead all around pallets with some kind of longitudinal mechanical locks into the floor? As above, do the straps augment these? Pallets or containers (collectively, "ULDs" or Unit Load Devices) are used for most cargo. The cargo floor is designed with rollers, rails, locks, and restraints to accommodate these ULDs and keep them from moving. When the cargo is too large or heavy for standard loading, a specific checklist must be used to accommodate a "floating" load that is not restrained by the built-in locks & restraints. Straps must be used to prevent movement in 3 dimensions, and the load from these straps must be distributed among enough tiedown lugs. |
Just to add a bit to what Intruder posted:
There is nothing inherently wrong with using fabric straps to secure a load - many synthetic materials are significantly stronger than equal weight steel (particularly in tension) and straps/ropes of these synthetic materials are routinely used for cargo retention. Some synthetic ropes used on ships are over a million pounds test. However the strength and number of tie downs must be appropriate to the load - regardless of the material. |
Ok, so why is that ? (i.e. no chains allowed) Pallet locks provide longitudinal (fore/aft) restraint of the pallet in the rail. But if the size of the pallets, or the spacing of the pallets does not line up with the rail locks, then straps must be used to provide longitudinal restraint. These straps MUST be preloaded. This is usually done with a large ratchet mechanism. If there is slack in the straps and the load is allowed to shift at all, the momentum of a shifting load can easily be much greater than the static load and either the strap or the tie down will fail. The straps must be roughly equally preloaded. If one strap is preloaded and the others are not, the preloaded strap/tiedown will take the entire load and fail. The load will then shift to the next tightest strap and overload it to failure. This continues for each strap in sequence, tightest to loosest, creating a "zipper" effect. In milliseconds all of the straps/tie downs will fail and the load will be free to move longitudinally. I'm not saying this is what happened on this flight, but that is how the system works (and can fail) on commercial cargo aircraft. This is VERY different than military airlifters. Hope this was helpful. |
Thanks Ken makes a lot of sense.
I had thought that perhaps a specially reinforced floor might have been installed in a cargo 747, but I can see how you explanation is lighter and still fit for purpose. That transcript is very sobering. It is almost as if they almost realised how dangerous what they may have seen was, but some complacency perhaps did not lead to enough caution over the risks. Maybe the load was infact re-secured after their discussion, but perhaps by then some of the straps had been critically weakened. |
Thank you, KenV, for that very good, clear, post.
JFZ90 - I doubt if they were complacent; I suspect they were tired. Sunbird123's post 682. The two conditions may look alike. |
All times are GMT. The time now is 20:35. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.