744 Override Jettison Pump Problem
On one of our CF6-powered 744's, a Technical Log report noted that in cruise the #3 Fore and Aft Override Jettison fuel pumps came on automatically with the CWT still containing 25 tonnes of fuel.
This seems to defy airplane logic. The wiring schematics show that each pump is controlled by separate relays and the logic in the Fuel System Management Card shows that a single logic gate controls four individual logic gates which control their respective O/J pump relays. If the card is getting false information, then all four O/J pumps should turn on.
Fuel balancing was required later on in the flight, so it wasn't just an indication error.
During normal ops, the O/J pumps require either of the following to operate:
1) Both CWT pumps turned off manually
2) Either CWT pump showing low pressure (after at least 5 minutes operation)
Any suggestions?
Thnx
NSEU