As a BA Boeing driver
I have found this thread very interesting, not only for the (lack of at times) accurate technical inputs but the perception of "non-drivers" regarding SOP's
With regard to SOP's it's all very well to say this is agreed with Boeings, the CAA or whoever so it must be OK, but is it?
For example, to dispatch a 757 with a rear booster pump u/s there is a requirement to carry extra fuel (for the approach situation to make sure the forward one is not uncovered if a GA was required) and also to open the crossfeed for the approach.
All very sensible you might say, but why on earth if the pump fails in flight does the QRH not at least require the crossfeed to be opened (obviously the extra fuel requirement cannot be met without a techstop)?
The response from Boeings (via BA) was that the chance of a fuel pump failure followed by a GA was so remote as to be ignored. But I ask you would airmanship suggest the crossfeed be opened? Alas no, not SOP's!
With regard to the public perception of "what’s left in the tanks" I am sure there are many out there that still think the tanks are filled full before every flight, and very few that are aware that, once airborne, (within certain constraints) the fuel "diversion" from Rwy **L can be the parallel Rwy **R!
They cannot understand how this re-planned operation, with all the support of Flight Planning (as they used to be known), Maintrol (with the appropriate Fleet Management's involvement) could result in a situation of the Captain transmitting a "Pan" call and then in his opinion having to change it to a "Mayday"
I will not speculate as to the reason, apart from suggesting that he obviously felt he did not have all the fuel in the tanks at his disposal!
With regard to comments made about pumps switched on without the synoptic showing it to be producing pressure as happening on occasions (because the fuel output pressure on that pump is lower than the others) could I ask the following question of 747-400 drivers (and perhaps those on other Boeings) and our helpful engineer at Manchester?
If with two tanks feeding any number of engines, with the crossfeed valve open ,what is to stop the rear pump with the highest pressure running the show? (once the fwd pumps are uncovered at low contents level with the increased attitude on the approach)
My perception of the system is that, the single "higher pressure" pump will supply all the fuel (assuming it can satisfy the total demand) and continue so to do until the tank is empty. Basic physics! Once the tank is empty and the "higher pressure" pump output pressure drops the pump in the other tank (lower pressure pump) would then supply all the engines.
All well and good, but would
you, as the driver, like to see the one tank supposedly not feeding once the crossfeed (SOP's) had been opened? I too would have used the magic (Mayday) word!
Obviously as the "normal" fuel feed with all engines running (once the centre and stab tanks are empty) is tank to engine. (glance at
http://www.meriweather.com/747/over/fuel.html)
It must have come as a bit of a shock (having carried out SOP's at low fuel levels and opened the crossfeed(s)), and on three engines to then be concerned (due to the fuel synoptic and tank quantity indications) regarding the perceived amount of useable fuel on board.
One last thought... I wonder after the IFSD, with the flight planners help, the re-plan (fuel calculation) suggested they could make it to Heathrow direct.