Couple of B744 fuel related MEL quesitons

[Richo Rob]

I have a couple of questions in relation to the B744 MEL fuel system:

(1) Reserve Tanks 2 & 3 Transfer Valves -
The MEL states that with all of them inop and with the Reserve Tanks themselves empty, we are allowed to fill up all the other tanks to max capacity. However, the MTOW is limited to 335.6t. What is the reason for this. Would it be because of the reduced wing bending relief with empty Reserve Tanks?

(2) Centre Wing Tank Override/Jettision Pumps -
The MEL states that one or both may be inop, and that any fuel actually carried in the CWT must be carried in lieu of payload ie. as part of ZFW. What would be the reason for this?

Any ideas much appreciated.

Rich

[LME (GOD)]

Ref the CWT mwl, it's beacause you would have a partial or non-existent ability to dump fueal out of the Centre, hence the MEL states that any fuel in the tank should be deemed unusable...i think :rolleyes:

[ACMS]

I have had 2 occasions where 1 or 2 CTR tanks pumps were inop and we had around 2.5 tonnes in the CTR tank. This fuel must be considered as payload as it may not be usable in-flight.
For this reason the effect it has on weight and balance and must be accounted for. Not just for T/O but especially for LDG. It may put the aircraft outside the forward limit for LDG.
Your manual should give the proceedure for this situation, it will be around -8 I.U. per tonne of fuel correction.
Hope that helps a little.

[Richo Rob]

The CoG reason for the CWT pumps seems reasonable to me.

With regards to the RT valves, can anybody confirm that the MTOW limitation is because of wing bending reasons?

The MEL for the RT valves also states that any CWT fuel must be carried in lieu of payload. We have discovered why this would be required for the CWT pump inop situation, but why is it also required for our RT valve inop situation? I don’t think in this case it would have anything to do with the CWT pumps failing, as that is for a completely different situation. How would the empty RTs effect the CWT fuel?

[Richo Rob]

Looking at other MELs for the fuel system, it seems some of the others also have the limitation about CWT fuel having to be carried in lieu of payload. For example, it also applies for the MEL for the X-feed valves, MT 1 & 4 boost pumps. Just wondering why they all fall back to this limitation?

[gas path]

Richo
The reason for the MEL limitations is,as you thought, for wing bending relief.
The limitation for CWT versus payload is the same you can carry CWT fuel or payload but not both.