This seems rather a lot of water. Are you sure?
This also surprised me when I read it in the Boeing 777 Maintenance Manual. I quoted it in an earlier forum posting, but I was hesitant. I really wanted to get more information from a higher source.
Re the CWT scavenging system. The flow rates were quoted before. It takes a long time to normally scavenge the CWT because of the diameter of the scavenge pipes, but even if all 138 gallons of ice thawed during the descent and was scavenged, would mixing it with over 3000 gallons of remaining wing tank fuel degrade the engine performance so much?
Note that the wing tank water scavenge pumps would also be operating to scavenge water from the wing tanks as it was coming from the CT.
Regards.
NSEU
P.S. BTW, many thanks to the guys suggesting possible solutions to my own engine hesitation/stalling problems. Spent many hours trying to figure out the fuel tank venting system on my car... Long gone are the days when a simple breather pipe was stuck in the air to vent fumes. Now the system is controlled by the engine management system! What a rat's nest! (miles of tubing, wiring, a charcoal filter, check valve, ECU controlled-solenoid valve, (car) rollover valve, etc). When the engine is hot, the fumes are injected into inlet manifold. A faulty venting system can cause poor idling and engine running rich.. or cause excessive fuel fumes.