Fuel System

Fuel System Failure

This fuel system transfers fuel so that no single pump failure above 25,000 feet will affect Military Thrust operation, as long as the forward tank gage indicates fuel. A pump failure is indicated when the forward tank/total quantity gage relationship shows an abnormal decrease in the forward tank gage reading at fuel flow rates less than 4000 pounds per hour.

Inflight Operation

If the BOOST PUMP INOP light comes on, fuel pressure to the engine has dropped below 5 psi, probably as a result of failure of one or more boost pumps. The following actions should be taken to prevent flameout:

1. Terminate afterburner operation.

   Note

   Afterburner should not be used when fuel in forward tank is less than 250 pounds.

2. Descend to below 25,000 feet.

3. All aircraft maneuvers should be as gentle as possible keeping the aircraft loading as near as possible to 1G. Avoid steep (20 degrees or more) nose-down attitudes.

4. Land as soon as practical. With fuel flows below 4000 pounds per hour, Military Thrust operation can be maintained above 25,000 feet with the most critical single pump failure, even though the forward tank gage approaches or indicates zero, provided the total quantity gage indicates 1700 pounds or more. Below 25,000 feet with the most critical pump failure, Military Thrust operation can be maintained as long as 600 pounds is indicated on the total quantity gage.

   Note

   Above 25,000 feet a failure of the intermediate tank transfer pump is considered the most critical. Below 25,000 feet, the most critical failure is a wing tank scavenge pump.

   Note

   With a failure of the intermediate tank transfer pump, afterburner operation can be maintained above 25,000 feet when the total fuel remaining is above 3100 pounds.

   Note

   With a failure of a wing tank scavenge pump, afterburner operation can be maintained below 25,000 feet when total fuel remaining is above 1700 pounds.

If a flame-out occurs under these conditions, an air start should be attempted. It may be necessary to descend to below 25,000 feet to accomplish an air start.