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-   -   Transferring fuel from centre tank on 777 (https://www.pprune.org/tech-log/614318-transferring-fuel-centre-tank-777-a.html)

punkalouver 13th Oct 2018 15:54
Transferring fuel from centre tank on 777
 
Seems like a good idea if you have a leak...how did they do it.

"C-FNNU, a Boeing 777-333ER aircraft operated by Air Canada, was conducting flight ACA890 from Toronto/Lester B. Pearson Intl, ON (CYYZ) to Rome/Leonardo da Vinci Intl, Italy (LIRF). During cruise flight in the vicinity of Prince Edward Island, the flight crew noticed that the fuel quantity in the centre tank was decreasing. The remaining fuel in the centre tank was transferred into the wings and the flight crew elected to return to CYYZ to have the aircraft inspected. The aircraft landed at CYYZ without further incident. The operator’s maintenance inspection determined that the left centre fuel discharge check valve was faulty, and replaced the unit in accordance with the manufacturer’s instructions."

BAengineer 13th Oct 2018 16:31
Walked out on to the wing and selected the refuel valve open?.

But seriously as you hint at - you cannot transfer fuel between tanks in flight. All you do is use center tank fuel before wing tank fuel - which is the normal operation of the system.

B-HKD 13th Oct 2018 23:25
Originally Posted by BAengineer (Post 10272985)
Walked out on to the wing and selected the refuel valve open?.

But seriously as you hint at - you cannot transfer fuel between tanks in flight. All you do is use center tank fuel before wing tank fuel - which is the normal operation of the system.
Actually on the B777-300ER, when either main tank is below 23,900kg and the center tank is below 15,900kg. A scavenge pump will transfer fuel to the main tanks. All the crew would have to do is turn off the center fuel pumps early. With these conditions being met, transfer would begin immediately. Normally the center fuel pumps aren't turned off until ~1,000kg remaining.

Note, the last 100 or so deliveries have slightly different trigger values.

BAengineer 14th Oct 2018 01:44
Reading the OP again it now makes sense - The crew didnt transfer any fuel. The issue was a simply an uncommanded fuel transfer from the center tank to the left main tank. A faulty Discharge Check Valve is cited in the FIM as a cause of this defect. (28-22 Task 849)

tdracer 14th Oct 2018 02:27
Originally Posted by B-HKD (Post 10282290)
Actually on the B777-300ER, when either main tank is below 23,900kg and the center tank is below 15,900kg. A scavenge pump will transfer fuel to the main tanks. All the crew would have to do is turn off the center fuel pumps early. With these conditions being met, transfer would begin immediately. Normally the center fuel pumps aren't turned off until ~1,000kg remaining.

Note, the last 100 or so deliveries have slightly different trigger values.
Perhaps a nit - but if I recall correctly, there are no scavenge pumps as such for the center fuel tank - rather it's an ejector type setup that uses the main tank pumps to scavenge the center tank.
Not sure if that setup would move fuel out of the center tank quicker than if you just kept sending it to the engines.

airseb 14th Oct 2018 08:41
the latest versions of the -300 have modified scavenge pumps in the center tank. these are real scavenge pumps, contrary to the older versions that only have ejector type pumps.
and using central fuel until it’s empty is SOP. a very simple and robust system.

Wizofoz 14th Oct 2018 20:36
Originally Posted by B-HKD (Post 10282290)
Actually on the B777-300ER, when either main tank is below 23,900kg and the center tank is below 15,900kg. A scavenge pump will transfer fuel to the main tanks. All the crew would have to do is turn off the center fuel pumps early. With these conditions being met, transfer would begin immediately. Normally the center fuel pumps aren't turned off until ~1,000kg remaining.

Note, the last 100 or so deliveries have slightly different trigger values.
Yes, but as SOP is to use center tank fuel first, this doesn't happen in normal ops.

punkalouver 15th Oct 2018 00:29
Originally Posted by BAengineer (Post 10282347)
Reading the OP again it now makes sense - The crew didnt transfer any fuel. The issue was a simply an uncommanded fuel transfer from the center tank to the left main tank. A faulty Discharge Check Valve is cited in the FIM as a cause of this defect. (28-22 Task 849)
Thanks,

Makes sense. The fuel transferred without crew input.

birdspeed 15th Oct 2018 07:17
It’s quite common on the 777 for the centre tank scavenge to only scavenge into one side. Never experienced it on the -300, and with the earlier scavenge I guest the imbalance could be quite marked. Quite concerning when you’re just about to set off across the pond.

aeo 18th Oct 2018 15:43
Common problem with the wideboy Boeing’s, discharge check valve fails open and fuel pumps overboard via surge tank. First item in the B777 fuel leak check list is record totaliser, turn Centre Pumps off and wait half an hour and confirm if leak still evident.


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