737NG Fuel AD
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Join Date: Jul 2006
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737NG Fuel AD
Here we go again with the fuel AD question. So last night I did my PC check and we had a double failure of the center tank fuel pumps. Ran the QRH and I mentioned to my FO to request vectors for landing since we had about 18000 lbs of fuel in the center tank. My inspector inquired about my decision and I explained to him it was based on the fuel AD that limits the MZFW exceedance by no more than 5000 LBS during climb and cruise and by 3000 lbs during the descent since we were using fuel from main tanks now. He seemed pretty confused and told me that the AD is for despatch rules only. I continued with the ride and changed my position, even though I am pretty sure I am right, as the old saying goes " cooperate graduate". Am I missing something or my instructor was wrong? Thanks to anyone and I apologize for the numbers in pounds instead of kilos for the European pilots.
Join Date: Jun 2000
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I thought it was always the case that any centre tank fuel, without full wings or any other limitation, was added to the 'load' and would be subjected to any max ZFW limitation. Simple, surely.
Join Date: Mar 2007
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This one's been bothering me when looking at fuel tankering.
The wing doesn't know the difference between pink quivering SLF, their baggage, freight-and center tank fuel, we very often fly both where the total of centre tank plus payload exceeds ZFW limits, yet no one bats an eyelid?
Apparently ballast fuel may be carried up to payload plus actual ZFW but the total not to exceed the ZFW limit, and it may not be considered useable due CofG problems which could result.
Is this "wings part empty", ctr tank not, only a LANDING restriction, in normal circumstances?
Alas the OMs various available to me are not particularly helpful and specific.
MEL/DDG for inoperative auto-shutoff of centre tank pumps also allows centretank fuel to a specified limit on landing, so any good hard info on this would be appreciated.
Yet another grey area in our inadequate and widespread flight manual culture.
The wing doesn't know the difference between pink quivering SLF, their baggage, freight-and center tank fuel, we very often fly both where the total of centre tank plus payload exceeds ZFW limits, yet no one bats an eyelid?
Apparently ballast fuel may be carried up to payload plus actual ZFW but the total not to exceed the ZFW limit, and it may not be considered useable due CofG problems which could result.
Is this "wings part empty", ctr tank not, only a LANDING restriction, in normal circumstances?
Alas the OMs various available to me are not particularly helpful and specific.
MEL/DDG for inoperative auto-shutoff of centre tank pumps also allows centretank fuel to a specified limit on landing, so any good hard info on this would be appreciated.
Yet another grey area in our inadequate and widespread flight manual culture.
Per Ardua ad Astraeus
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Essentially it is the 'wing root bending moment' that governs. We are required to load full wings and use ctre tank first. Thus the decreasing weight of the ctre tank fuel is constantly 'offset' at the root by the wing fuel weight. The wing root is stressed to carry this weight.
Now shut off the ctre tank and feed only from the wings. The weight 'carried' by the root is no longer offset by full wings and so ZFW becomes a consideration. This used to be a 737NG pre-mod problem in the days when we tried to avoid fuel frost icing and we had to then factor the 'dead' ctre tank weight into 'payload'. Essentially the fuel instantly becomes 'payload' in that situation although that seems a little bizarre! Of course the wing root issue would not instantly become a problem, but would grow as wing fuel weight reduced, becoming a 'max.' issue as you say, at landing. In the 'pre-mod' days we could alleviate this if we saw a problem by using more ctre tank fuel to bring the 'notional' ZFW into limit.
Now shut off the ctre tank and feed only from the wings. The weight 'carried' by the root is no longer offset by full wings and so ZFW becomes a consideration. This used to be a 737NG pre-mod problem in the days when we tried to avoid fuel frost icing and we had to then factor the 'dead' ctre tank weight into 'payload'. Essentially the fuel instantly becomes 'payload' in that situation although that seems a little bizarre! Of course the wing root issue would not instantly become a problem, but would grow as wing fuel weight reduced, becoming a 'max.' issue as you say, at landing. In the 'pre-mod' days we could alleviate this if we saw a problem by using more ctre tank fuel to bring the 'notional' ZFW into limit.
