Issue: Fuel Pump Logic during Fuel Imbalance with Right Hand Engine Shutdown

[chrisarrow 1]

There is a fault in the logic of the Fuel Pump behavior in the scenario of Right Hand engine shut down while attempting to re-balance the fuel.

 

Here is the scenario:

 

Right Engine suffers a failure, engine is shutdown in accordance with the checklist. APU is also started in accordance with the checklist.

 

High Fuel Flow from the Left Hand Engine comparative to the zero fuel flow from the now failed right engine leads to a FUEL IMBALANCE scenario with the Left-Hand Tank being of lower quantity.

 

FUEL IMBALANCE checklist is carried out, which involves turning on either CROSSFEED VALVE and turning off the LEFT FWD and AFT Fuel Pumps switches.

 

30 minutes later, fuel is continuing to drain from the left hand tank at a faster rate.... WHY?

 

If you look at the FUEL SYNOPTIC you will note the Left FWD AC Pump is still running and providing fuel from the LEFT WING TANK to both the LEFT ENGINE and the APU. This is incorrect logic, in this situation you will never be able to balance the tanks, unless you turn off the APU.

 

ONLY on the ground will the LEFT FWD AC Pump operate in this situation. In flight the correct action of turning the LEFT FWD AC Pump switch OFF should be that the pump stops operating. APU fuel will be provided from the RIGHT MAIN AC Pumps via the cross-feed valves and the left fuel manifold.

 

 

Source: Real Life 777 Pilot, and Boeing 777 FCOM 1 Systems 

[777simmer 117]

There is a fault in the logic of the Fuel Pump behavior in the scenario of Right Hand engine shut down while attempting to re-balance the fuel.

 

Here is the scenario:

 

Right Engine suffers a failure, engine is shutdown in accordance with the checklist. APU is also started in accordance with the checklist.

 

High Fuel Flow from the Left Hand Engine comparative to the zero fuel flow from the now failed right engine leads to a FUEL IMBALANCE scenario with the Left-Hand Tank being of lower quantity.

 

FUEL IMBALANCE checklist is carried out, which involves turning on either CROSSFEED VALVE and turning off the LEFT FWD and AFT Fuel Pumps switches.

 

30 minutes later, fuel is continuing to drain from the left hand tank at a faster rate.... WHY?

 

If you look at the FUEL SYNOPTIC you will note the Left FWD AC Pump is still running and providing fuel from the LEFT WING TANK to both the LEFT ENGINE and the APU. This is incorrect logic, in this situation you will never be able to balance the tanks, unless you turn off the APU.

 

ONLY on the ground will the LEFT FWD AC Pump operate in this situation. In flight the correct action of turning the LEFT FWD AC Pump switch OFF should be that the pump stops operating. APU fuel will be provided from the RIGHT MAIN AC Pumps via the cross-feed valves and the left fuel manifold.

 

 

Source: Real Life 777 Pilot, and Boeing 777 FCOM 1 Systems

 

I have noticed the same and submitted a ticket about this already. It cant hurt if you do the same though.

[nawarren 83]

Hi All,

 

I also raised this question some while ago. Good to know it wasn't something I was doing wrong!

 

Cheers

 

Neil