BOAC - haven't done it myself, but have seen it happen once ... and the heated exchange between engineer on ground and engineer in cockpit
SOPS - just a point of clarification. The three AOM limitations wrt Fuel disposition are: if more than 453kg fuel is to be loaded in the CTR Tank the Mains must be full, the lateral imbalance between #1 & #2 must be scheduled to zero and the random imbalance is not to exceed 453kg at any stage from T/O to LDG.
The normal procedure
recommendation is to switch ON the CTR Pumps only
if CTR Tank fuel quantity
exceeds 453kg. ON is preferable anyway because you don't want extended APU ops to create an imbalance before you even get around to pushback (cf limitation #2).
I discovered pretty quickly that light-weight departures with around 10.0 FOB can get a nuisance caution on rotation because the fuel shifts back uncovering the ports in the CTR Tank - they're longitudinally displaced (the L/R CTR pumps are physically in the respective Main Tank
BOAC you must be on NG's) - from memory the right CTR Pump starves first, but someone please correct me.
.
When established in a level attitude cruise, if the CTR tank contains useable fuel and the CTR tank pumps switches are off, the CTR tank pump switches should be positioned ON again. If the CTR tank contains more than 453kg, the CTR tank pump switches must be turned ON.
This alone suggests that for T/O and CLM it's permissible to have the CTR pumps off - they just have to be back on by cruise. I'm sure if Boeing thought the wings were going to fold up for 500kg (x2) burnoff out of the Mains they would have been a little more strict in their wording. So you can rest in the comfort you are not defying the AOM
Incidently, we turn ours off when we line up and back on once accelerating out of min manouevring to 250.
... still friends?
Oh yeah, BOAC - I was told the six pumps were all "identical" - same nominal flow rate, same pressure (30psi, flow rate is dependant) - the difference was all in the check valves. The CTR tank check valves are adjusted lower. The only difference comes about when you have the AUX tanks fitted in the aft hold. AUX fuel must be used before CTR fuel (can't imagine why
) and therefore has the higher pressure "mother of all pumps" to beat the rest into the left fuel manifold.