Fault-tolerant fuel isolation from engine firebay

1. A system for use in isolating fuel from an aircraft firebay, the system comprising:

a fuel tank;

an airframe fuel pump;

an engine located within the aircraft firebay;

a firewall separating the aircraft firebay from a volume containing the fuel tank and the airframe fuel pump;

a fuel feed line extending from the fuel tank to the airframe fuel pump and through the firewall to the engine, the fuel feed line fluidly connecting the fuel tank to the engine and additional aircraft systems, wherein the airframe fuel pump is configured to pump fuel from the fuel tank through the fuel feed line to the engine, wherein the fuel feed line comprises a cold side portion extending from the fuel tank to the firewall and a hot side portion extending from the firewall to the engine;

a connector coupled inline with the fuel feed line at a location of the cold side portion of the fuel feed line;

a valve coupled to the connector, the valve configured in a normally closed orientation;

an air feed line coupled to an ullage portion of the fuel tank and to the valve; and

a control unit configured to control operation of at least the airframe fuel pump and the valve, wherein in the event of an engine fire, the control unit is configured to output control signaling to:

turn off the airframe fuel pump to stop pumping the fuel through the fuel feed line; and

open the valve to introduce air from the ullage portion of the fuel tank into the fuel feed line, wherein the air introduced by the valve provides a siphon break in the fuel line such that the fuel cannot be siphoned and the only fuel that can pass the firewall is the remaining fuel in the fuel feed line downstream of the connector and the introduced air.

2. The system of claim 1 , wherein the fuel feed line does not include a shut off valve in the cold side portion of the fuel feed line extending from the fuel pump to the firewall.

3. The system of claim 1 , wherein in the event of the engine fire, the control unit is configured to output control signaling to turn off the engine.

4. The system of claim 1 , wherein the aircraft further comprises one or more propellers, wherein in the event of the engine fire, the control unit is configured to output control signaling to cause the feathering of the one or more propellers.

5. The system of claim 1 , further comprising a jettison valve fluidly connected to the fuel tank, wherein in the event of the engine fire, the control unit is configured to output control signaling to open the jettison valve for a period of time to reduce pressure in the fuel system.

6. The system of claim 1 , wherein in the event of the engine fire is not an actual engine fire, the control unit is configured to output control signaling to:

start the engine;

turn on the airframe fuel pump; and

close the valve such that the fuel will resume flowing to the engine.

7. The system of claim 1 , wherein in the event of a failure of the valve such that it is at least partially open when there is not an engine fire, the fuel continues to flow at a sufficient level through the fuel feed line and the connector from the fuel tank to the engine to allow for safe operation of the engine.

8. The system of claim 7 , wherein in the event of the failure of the valve such that it is at least partially open when there is not an engine fire, a portion of the fuel flowing through the fuel feed line is diverted through the valve to the fuel tank via the air feed line.

9. The system of claim 1 , wherein the connector is coupled inline with the fuel feed line at a high elevation location of the cold side of the fuel feed line, the high elevation location at or above an elevation corresponding to a low elevation point of the ullage portion of the fuel tank.

10. The system of claim 1 , wherein the connector is coupled inline with the fuel feed line at a high elevation point location of the cold side of the fuel feed line.

11. The system of claim 1 , wherein the connector comprises a tee connector coupled inline with the fuel feed line and coupled to the valve.

12. The system of claim 1 , further comprising one or more sensors proximate to the engine and configured to detect a condition indicative of an engine fire and provide sensor signaling to the control unit.

13. The system of claim 12 , wherein the control unit is configured to:

receive the sensor signaling;

transmit a message to a pilot to indicate the detection of the condition indicative of the engine fire;

receive a command from the pilot to initiate fuel isolation; and

output control signaling to turn off the airframe fuel pump to stop pumping the fuel through the fuel feed line and to open the valve to introduce the air into the fuel feed line.

14. The system of claim 12 , wherein the control unit is configured to:

receive the sensor signaling;

based on at least the received sensor signaling, determine that fuel isolation is needed; and

output control signaling to turn off the airframe fuel pump to stop pumping the fuel through the fuel feed line and to open the valve to introduce the air into the fuel feed line.

15. The system of claim 1 , wherein the aircraft comprises one of a manned aerial vehicle and an unmanned aerial vehicle.

16. The system of claim 1 , wherein the aircraft comprises one of multi-engine aircraft and a single engine aircraft.

17. A method for isolating fuel from an aircraft firebay, the method comprising:

in the event of an engine fire,

turning off an airframe fuel pump to stop pumping the fuel through a fuel feed line fluidly connecting a fuel tank to an engine within the aircraft firebay and passing through a firewall that separates the aircraft firebay from a volume containing the airframe fuel pump and the fuel tank;

opening a valve coupled to a connector coupled inline with the fuel feed line at a location of a cold side portion of the fuel feed line, wherein the cold side portion of the fuel feed line extends from the fuel tank to the firewall, and wherein a hot side portion of the fuel feed line extends from the firewall to the engine, wherein the valve is in a normally closed orientation; and

introducing, by opening the valve, air from an ullage portion of the fuel tank into the fuel feed line to provide a siphon break in the fuel line such that the fuel cannot be siphoned and the only fuel reaching the engine is the remaining fuel in the fuel feed line downstream of the connector and the introduced air, the air received from an air feed line coupled to the ullage portion of the fuel tank and to the valve.

18. The method of claim 17 , wherein the fuel feed line does not include a shut off valve in the cold side portion of the fuel feed line extending from the fuel pump to the firewall.

19. The method of claim 17 , further comprising:

in the event of the engine fire,

outputting, by a control unit, signaling to turn off the airframe fuel pump and to open the valve.

20. The method of claim 17 , wherein in the event of the engine fire,

outputting, by the control unit, control signaling to turn off the engine.

21. The method of claim 17 , wherein in the event of the engine fire,

outputting, by the control unit, control signals to causing the feathering one or more propellers of the aircraft.

22. The method of claim 17 , further comprising:

in the event of the engine fire,

opening a jettison valve fluidly connected to the fuel tank for a period of time to reduce pressure in the fuel system.

23. The method of claim 17 , wherein in the event of the engine fire is not an actual engine fire, the method comprises:

outputting, by the control unit, control signaling to start the engine, to turn on the airframe fuel pump and to close the valve such that the fuel will resume flowing to the engine.

24. The method of claim 17 ,

wherein in the event of a failure of the valve such that it is at least partially open when there is not an engine fire,

flowing fuel at a sufficient level through the fuel feed line and the connector from the fuel tank to the engine to allow for safe operation of the engine.

25. The method of claim 24 ,

wherein in the event of the failure of the valve such that it is at least partially open when there is not an engine fire,

diverting a portion of the fuel flowing through the fuel feed line through the valve back to the fuel tank via the air feed line.

26. The method of claim 17 , wherein the connector is coupled inline with the fuel feed line at a high elevation location of the cold side of the fuel feed line, the high elevation location at an elevation corresponding to a low elevation point of the ullage portion of the fuel tank.

27. The method of claim 17 , wherein the connector is coupled inline with the fuel feed line at a high elevation point location of the cold side of the fuel feed line.

28. The method of claim 17 , wherein the connector comprises a tee connector coupled inline with the fuel feed line and coupled to the valve.

29. The method of claim 17 , further comprising:

detecting, by one or more sensors proximate to the engine, a condition indicative of an engine fire; and

providing sensor signaling to the control unit.

30. The method of claim 29 , further comprising:

receiving, at the control unit, the sensor signaling;

transmitting a message to a pilot to indicate the detection of the condition indicative of the engine fire;

receiving a command from the pilot to initiate fuel isolation; and

outputting control signaling to initiate the steps of turning off the airframe fuel pump, opening the valve, and introducing the air.

31. The method of claim 29 , further comprising:

receiving, at the control unit, the sensor signaling;

determining, based on at least the received sensor signaling, that fuel isolation is needed; and

outputting control signaling to initiate the steps of turning off the airframe fuel pump, opening the valve, and introducing the air.

32. The method of claim 17 , wherein the aircraft comprises one of a manned aerial vehicle and an unmanned aerial vehicle.

33. The method of claim 17 , wherein the aircraft comprises one of a multi-engine aircraft and a single engine aircraft.

34. An apparatus for isolating fuel from an aircraft firebay, the apparatus comprising:

a non-transitory storage medium storing a set of computer readable instructions; and

a control unit comprising a control circuit configured to execute the set of computer readable instructions which causes to the control unit to:

output, in the event of an engine fire, control signaling to turn off an airframe fuel pump to stop pumping the fuel through a fuel feed line fluidly connecting a fuel tank to an engine within the aircraft firebay and passing through a firewall that separates the aircraft firebay from a volume containing the airframe fuel pump and the fuel tank; and

output, in the event of the engine fire, control signaling to open a valve coupled to a connector coupled in line with the fuel feed line at a location of a cold side portion of the fuel feed line, wherein the cold side portion of the fuel feed line extends from the fuel tank to the firewall, and wherein a hot side portion of the fuel feed line extends from the firewall to the engine, wherein the valve is in a normally closed orientation, wherein air from an ullage portion of the fuel tank is introduced into the fuel feed line to provide a siphon break in the fuel line such that the fuel cannot be siphoned and the only fuel passing the firewall is the remaining fuel in the fuel feed line downstream of the connector and the introduced air, the air received from an air feed line coupled to the ullage portion of the fuel tank and to the valve.

35. The apparatus of claim 34 , wherein the control unit is configured to:

output, in the event of the engine fire, control signaling to turn off the engine; and

output, in the event of the engine fire, control signaling to cause the feathering one or more propellers of the aircraft.

36. A system for use in isolating fuel from a vehicle firebay, the system comprising:

a fuel tank;

a fuel pump;

an engine located within the vehicle firebay;

a firewall separating the vehicle firebay from a volume containing the fuel tank and the fuel pump;

a fuel feed line extending from the fuel tank to the airframe fuel pump and through the firewall to the engine, the fuel feed line fluidly connecting the fuel tank to the engine and additional vehicle systems, wherein the fuel pump is configured to pump fuel from the fuel tank through the fuel feed line to the engine, wherein the fuel feed line comprises a cold side portion extending from the fuel tank to the firewall and a hot side portion extending from the firewall to the engine;

a connector coupled inline with the fuel feed line at a location of the cold side portion of the fuel feed line;

a valve coupled to the connector, the valve configured in a normally closed orientation;

an air feed line coupled to an ullage portion of the fuel tank and to the valve; and

a control unit configured to control operation of at least the fuel pump and the valve, wherein in the event of an engine fire, the control unit is configured to output control signaling to:

turn off the fuel pump to stop pumping the fuel through the fuel feed line; and

open the valve to introduce air from the ullage portion of the fuel tank into the fuel feed line, wherein the air introduced by the valve provides a siphon break in the fuel line such that the fuel cannot be siphoned and the only fuel that can pass the firewall is the remaining fuel in the fuel feed line downstream of the connector and the introduced air.