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Bagram 747 CG shift with increased fuel

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Bagram 747 CG shift with increased fuel

Old 12th May 2013, 08:43
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Bagram 747 CG shift with increased fuel

I am wondering how much different the cg would have been for the takeoff out of Bagram vs the earlier takeoff en route to Bagram? It is my understanding that the Bagram takeoff was with a heavier fuel load. Could that difference have contributed to the appearant difficulty keeping the nose from pitching too high?
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Old 12th May 2013, 09:48
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What do you think crews/dispatchers do with trim calculations when the fuel load changes (every trip)?
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Old 12th May 2013, 10:24
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Of course, the calculated trims accuracy depends upon the actual load and fuel being of the same weight and in the same positions as used in the calculations.
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Old 13th May 2013, 16:18
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BOAC and Onceapilot - thanks for the responses. I know that a proper weight/balance determination is made for every takeoff and should have caught the cg being out of range if it was. I am just trying to identify any possible contributing factors to the puzzling detail that the the takeoff heading to Bagram went off okay while the one out of Bagram led to the accident. From what I have gleamed from the discussion here, the only significant weight/balance change between these two takeoffs was more fuel for the second.

Is it possible that the weight/balance determination for the first flight was incorrect, but that with less fuel the cg was in an acceptable range? If the same, incorrect, cargo weight/distribution data was then used prior to the ill-fated takeoff it might have shown the cg to be within range with more fuel when it actually was not.
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Old 13th May 2013, 17:14
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Originally Posted by FCEng
Is it possible that.....
- at this stage, for we armchair QBs MANY THINGS are possible, some things are more likely.

Last edited by BOAC; 13th May 2013 at 17:53.
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Old 13th May 2013, 20:34
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About 41-42% MAC. The aft limit being 33% MAC.

The Korean -400F with the loadsheet error, landed with 40.2% MAC. Its nose wheels were not touching the ground anymore when the aircraft came to a full stop.

Last edited by B-HKD; 13th May 2013 at 20:34.
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Old 13th May 2013, 20:43
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B-HKD - That's sobering to get the W/B that far off.

I've loaded aft CG where the nose wheel extends a little bit but to imagine it being off the ground is just amazing to consider. Can only imagine how it flew.
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Old 14th May 2013, 00:35
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Just to go off on a tangent slightly with regards the Korean Air 747- if you discovered whilst in the air that your fuel load was way off, is it possible in a 747 to select a certain combination of tanks and bring the aircraft closer to correct trim by burning/ dumping fuel?
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Old 14th May 2013, 01:11
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the -400F -400BCF (as involved in the Bagram accident) -400BDSF -400ERF do not have activated stab tanks. So thats out of the question.

As the center tank quantity decreases and wing fuel from the main tanks (wings) is burned off, the CG continues to move aft.

Landing ASAP before it gets worse comes to mind.

Had it not been for the crew of the Korean -400F contacting load control at HQ in Seoul, immediately after takeoff and them telling the relief pilot and captain to go downstairs to move pallets forward, the plane would have landed with more than 43.7% MAC CG. Some 10.7% aft of the limit!

Considering the CG was 37.8% MAC at takeoff (4.8% aft of the limit) and not including the subsequent load shift by the crew, the resulting fuel burnoff to Seoul would have resulted in a CG shift of 5.9% MAC.

Amazing that HQ advised them to continue or that the captain didnt just land immediately at Oslo overweight with a CG 4.8% MAC aft of limit instead of the 7.2% MAC aft of limit at Seoul. Again, land ASAP comes to mind.


In the case of the National -400BCF, the aircraft was obviously not airborn anywhere near enough time for a burnoff of center tank and most of the wings to result in the CG moving AFT.

Last edited by B-HKD; 14th May 2013 at 01:19.
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Old 14th May 2013, 01:12
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Just to go off on a tangent slightly with regards the Korean Air 747- if you discovered whilst in the air that your fuel load was way off, is it possible in a 747 to select a certain combination of tanks and bring the aircraft closer to correct trim by burning/ dumping fuel?
Yep.
Too nose-heavy move fuel out of the centre wing tank and/or tanks 2/3.
Too tail heavy move fuel out of tanks 1/4.
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Old 14th May 2013, 01:18
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Yep.
Too nose-heavy move fuel out of the centre wing tank and/or tanks 2/3.
Too tail heavy move fuel out of tanks 1/4.
I assume this involves burning fuel directly from the tanks you mentioned, and not actually moving it elsewhere correct? (Via 1&4 and 2&3 xfeed)
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Old 14th May 2013, 02:10
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You could use the Fuel Transfer Main 1 & 4 switch to move the C of G forward.

Creative fuel pump selections with all the X feeds open using the jettison system would get the C of G aft quickly but only to a point system logic would cause reserves to tranfer as normal moving the c of g forward or stabilizing it, you could stop the jettison and continue to "burn" the c of g aft again with x feeds all open and creative fuel pump selections.
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Old 14th May 2013, 02:46
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After rechecking the video at the 1 second mark after the 747 enters view.

At that instant in time I get a pitch of 43 degrees with a standard deviation of 2 degrees for 5 close snap shots.

The 747 is at 970 ft agl and 4400 ft away from camera (along ground). The 747 is 7800 ft from the T/O threshold (along ground) of the 11819 ft runway length.

If you have doubts please do your own calculations and let me know your numbers.

- Use the best video available.
- Google Earth
- Google Maps
- Airport map
- Most good video players
- Any decent Photoshop software
- 747F dimensions (Boeing)
- Get meters/pixel (object dependant)
- Get degrees/pixel
- Trigonometry
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Old 14th May 2013, 04:41
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[Cryptic acronyms we can probably do without - JT].
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Old 14th May 2013, 10:33
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This has come from a reliable source:-



FYI, I'm in IBT Go-Team training in DC with NTSB and others, and Director of NTSB Office of Aviation Safety briefed us on this accident today. This is accurate info from NTSB source today:



The CVR/FDR on the accident aircraft stopped working on rotation; engine/fuselage/tail parts were located on the runway. A total of (7) MRAP armored vehicles were being carried as cargo. NAC was the only civil DoD contract carrier who will carry these vehicles. Aircraft loaded at Camp Bastian, not Bagram, was stopping in Bagram for fuel. Aircraft uplifted 48,000 lbs of fuel at Bargram for flight to DXB. After impact, 1 MRAP vehicle was deeper in the impact crater than any aircraft/fuselage parts.
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Old 14th May 2013, 14:50
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The CVR/FDR on the accident aircraft stopped working on rotation;
Huh??
engine/fuselage/tail parts were located on the runway.
What would that be from? tail bounce on take off?? (Hmm, damage to elevators/horizontal stab? Would not some of the eyewitnesses previously cited have mentioned this?
A total of (7) MRAP armored vehicles were being carried as cargo.
Different from some folks who have carried that cargo and their inputs in the currently locked thread at R & N. .
NAC was the only civil DoD contract carrier who will carry these vehicles.
??? Is this deemed significant?
Aircraft loaded at Camp Bastian, not Bagram, was stopping in Bagram for fuel. Aircraft uplifted 48,000 lbs of fuel at Bargram for flight to DXB.
Consistent with previous info ...
After impact, 1 MRAP vehicle was deeper in the impact crater than any aircraft/fuselage parts.
Not sure of significance.

It will be interesting to match this leak with the reports that are eventually issued by NTSB in support of the local authorities.

Last edited by Lonewolf_50; 14th May 2013 at 14:51.
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Old 14th May 2013, 15:03
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NAC was the only civil DoD contract carrier who will carry these vehicles.
False.



A total of (7) MRAP armored vehicles were being carried as cargo.
False again.

Cant fit 7 MRAPs in a -400BCF or any onther -400 freighter.

World manages 6 with some clever loading.

The majority of other carriers load 5.


Pretty safe to say this 'reliable' source and the alleged information leaked from the briefing is pure BS.
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Old 14th May 2013, 15:32
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Snoop

Had it not been for the crew of the Korean -400F contacting load control at HQ in Seoul, immediately after takeoff and them telling the relief pilot and captain to go downstairs to move pallets forward, the plane would have landed with more than 43.7% MAC CG. Some 10.7% aft of the limit!
Just out of interest. I thought all power was removed from the cargo PDU's with engines running and certainly in the air. Maybe some superhuman strength kicked in when the panic struck?
A fully loaded pallet is not easy to shift, especially if the base is distorted.
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Old 14th May 2013, 15:48
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B-HDK: given the options, I'll lay my betting money on your estimate.
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Old 14th May 2013, 21:30
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Originally Posted by B-HKD View Post
About 41-42% MAC. The aft limit being 33% MAC.

The Korean -400F with the loadsheet error, landed with 40.2% MAC.
Interesting!
Just out of curiosity I was tempted to do some rough guestimates/calcs.
Don't shoot me for it this is not meant to speculate on the cause, just checking some plausibilities and orders of magnitude.

So let's have a look:
Mean aerodynamic chord of the 747 is 327,8 inches. (http://www.boeing.com/assets/pdf/com...misc/A20WE.pdf).
7% of that would mean 22,95 inches. (Korean managed to take off with ~38% so let's assume KAL + 2% for a likely unrecoverable config for takeoff).
So the Cg of the aircraft would have to be ~23 inches behind the aft Limit in a case where the front wheel almost lifts off the ground.
If we assume a TOW of roundabout 300.000kg an MRAP weight of ~12000kg a single MRAP would havce to shift a whopping 573 inches to get that sort of Cg shift.
If we instead assume they added 25.000 kg of fuel that would require the added fuel to be stored ~275 inches behind aft Cg to achieve the same shift.
Question to the 747 experts: Is that technically possible?

Anyway These rough calcs give me the Feeling there is really a massive load shift required to get into a seriously tail heavy config. And the KAL was still able to land safely.

The more one looks into it the more puzzling it gets.

Last edited by henra; 14th May 2013 at 21:37.
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