Max ZFM limits - why?
 

Hello fellow pilots,

I have again some Q. We have on 737 this limit: Main tanks 1 and 2 must be full if center tank contains more than 1000lbs/453 kg.

And now the Q.: When becomes this limitations critical? Assuming we are on MZFM.

Is it during ground ops., isn`t it?

I am not totally sure what question you are trying to ask. However, this limitation is never a problem in operating the aircraft as you should always have burnt the centre tank fuel first. I guess you could get caught out if for some reason you forgot to use the centre tank fuel and had more than 453kg in there, necessitating full mains.

That`s clear. I know the MZFM limits are becauce of forces between fuselage and wing, but the question was: when is this limit most critical in flight, when there are lift and gravity forces or on ground when there are only gravity forces?

Otherwise, the wings may snap off. They can only take so much weight.

Actually you can get caught out fairly easily on a shortish tankering sector, and many have. If you have less than 2300kg in the ctr tank you can't use the fuel until your airborne and there are limits even then in both climb and descent. Re-routes can also contribute to putting you over.

My understanding is that its significant on the ground due to wing bending relief but I could be wrong there.

In flight wing root bending relief consideration .. otherwise the MZFW limit would have to be applied in a more conservative manner.