infrequentflyer789 (#1978)
- Agree about noise and switch-off of OJ pumps.
- I have been through posts but not seen centre tank scavenge inlets, OJ pump inlets or drain valves relative to each other or side on view as to how far off floor. Of few pictures have seen, they include:
Sumping -
http://panchromat.org/.misc/B777-doc...stallation.jpg Vent picture -
http://panchromat.org/.misc/B777-doc...ent_system.jpg Pump -
http://panchromat.org/.misc/B777-doc...stallation.jpg Centre tank -
http://www.pprune.org/3929959-post284.html Engine fuel supply –
ImageShack - Hosting :: 777engineug1.jpg RR Trent parameters -
http://rgl.faa.gov/Regulatory_and_Gu...E/E00050EN.pdf Plan of fuel supply:
ImageShack - Hosting :: 777fuelpw3.jpg
- Agree re burn rate - slight difference in main tank flow rate just before and then after scavenge finishes.
- Agree re context of remark in AAIB report - my point was more that it seemed to suggest if gas then why not fluid could move through inactive OJ pump with suitable pressure differential? [I had an obscure "March Hare" theory a few posts back that air might be dissolved/entrained into main tank fuel as result of operation of centre tank fuel scavenge when CWT dry and as a result (i) subsequent release of undissolved air from air-saturated fuel into suction feed pipe and/or fuel manifold near OJ/ jettison check valve [or, before cavitation (as cause) ruled out, in HP pump] and (ii) so suction feed restricted by undissolved air and/or undissolved air near OJ/ jettison check valve end might allow localised low pressure fluctuations induced by cycling to result in OJ/ jettison check valve opening if surge of pressure in centre tank on fast descent, thereby introducing water slug (not air) to fuel manifold. In my dream world both the Mad Hatter and March Hare were coming to tea.]
- Agree that will have compared fuel data and that of previous flight.
Anyway it seems there is still quite a bit of Boeing testing to be done on the cascade of contributory factors leading to the location of the 95% restriction in the underlying fuel system, and the tentative, conflicting scenarios to date.
Perhaps the expense of putting a bit more flight test kit where not normally found in tanks and supply lines of a real plane (with correct geometry) and then flying it would be worth it (maybe could add water to centre tank and lower the temp of fuel in one of the main tank before uplifting it to cut to the chase, etc) ... since a double rollback is not just unusual but after all a surprisingly serious failure condition in an otherwise excellent aircraft.