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 gauge indicates fuel. A pump failure is indicated when the forward tank/total quantity gauge relationship shows an abnormal decrease in the forward tank gauge reading at fuel flow rates less than 4,000 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 1 G. Avoid nose-down attitudes in excess of 20°.

  4. Land as soon as practical.

    Note

    With fuel flows below 4,000 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 gauge approaches or indicates zero, provided the total quantity gauge indicates 1,700 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 gauge.

    Note

    T ransfer of fuel by gravity from the wing tank can be increased by decelerations, yaws, and slips.

    Caution

    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.

    Caution

    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 3,100 pounds.

    Caution

    With a failure of a wing tank scavenge pump, afterburner operation can be maintained below 25,000 feet when total fuel remaining is above 1,700 pounds.

    Warning

    If a flame-out occurs due to depletion of the fuel from the forward tank, move the throttle to the IDLE position to allow fuel transfer to the forward tank and descend to 25,000 feet before attempting an air start.