15th Aug 2012, 12:29
When departing with max fuel on the B744 (fitted with HST) is it the norm to already have the L and R STAB pump switches on before departure?
I am aware that the pumps won't actually run until the logic commands the feed to the CWT (CWT fuel approx. < 37,000Kgs).
So to sum it up, do you put them on from the start until the HST transfer begins automatically and is complete, or do you wait for the EICAS advisory to turn hem on so that transfer to the CWT can begin?
15th Aug 2012, 13:09
UK operator: turn them on and off according to EICAS
15th Aug 2012, 19:07
I suspect that only turning on the pumps when prompted to by the EICAS is a procedure that has been in place from the beginning on the 744.
Anyone know why they arent just put on (armed) like all other MAIN tanks before start?
15th Aug 2012, 19:13
We wait for the EICAS message during climb. We'll get an EICAS message on the ground if the HST pumps are on according to the FCOM.
15th Aug 2012, 21:16
I found the >FUEL PMP STB L and >FUEL PUMP STB R EICAS advisories in the FCOM I have, as you mentioned. Makes perfect sense now why they are not armed on the ground.
I do wonder why the advisory was implemented in the first place for a fueled HST with pumps ON (ARMED) on the ground. Would make sense to have it set up properly before departure and just wait for the logic to activate the pumps.
16th Aug 2012, 10:25
That's how it was some years ago - turn the HST pumps on pre start and turn them off when the EICAS said so. Remember the pump overheat incidents? That changed Boeing thinking to more closely control the pumps to ensure they were never run dry, hence the current proceedure.
16th Aug 2012, 18:54
That obviously explains the change in procedure. Thanks mustafagander.
I did some reading on the auto-shutoff SB etc. I know not all aircraft had it implemented, but there was a slight change in the EICAS advisory logic and the >FUEL PMP STAB L/R message as the FCOM shows (One of the FCOM's I have covers both pre SB and implemented SB)