744 Fuel Pump Logic
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744 Fuel Pump Logic
A statement in our 744 AOM regarding fuel pump logic seems to differ from what I have seen on the flight deck.
"#2 & #3 Tank Override/Jettison pumps are inhibited from operating when pressure is detected from both CWT override/jettison pumps."
This suggests to me that pressure has to be detected from the output of both pumps before the inhibit is active. However, in the following photograph, it is shown that one CWT pump has inhibited all the OJ pumps (blue colour).
OJ Pump Inhibit
Our wiring schematic logics suggest that this photograph is correct (Edit: the low pressure inhibit logic has a 5 minute delay).
I'm not saying our AOM is incorrect at this point (I have been told other airline AOM's say the same thing). Have I overlooked something?
Thanks in advance.
Rgds.
NSEU
"#2 & #3 Tank Override/Jettison pumps are inhibited from operating when pressure is detected from both CWT override/jettison pumps."
This suggests to me that pressure has to be detected from the output of both pumps before the inhibit is active. However, in the following photograph, it is shown that one CWT pump has inhibited all the OJ pumps (blue colour).
OJ Pump Inhibit
Our wiring schematic logics suggest that this photograph is correct (Edit: the low pressure inhibit logic has a 5 minute delay).
I'm not saying our AOM is incorrect at this point (I have been told other airline AOM's say the same thing). Have I overlooked something?
Thanks in advance.
Rgds.
NSEU
Could the apparent discrepancy be down to the balancing function of the 2/3 jett/overrides? They operate to provide lateral balancing during jettison, so, possibly ANY CWT output pressure would act as an inhibitor to prevent imbalance. If I can find my manuals, I'll see if that makes any sense!! 
