In-flight refueling systems

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IN-FLIGHT REFUELING SYSTEMS

Air refueling systems permit complete in-flight or on the ground refueling of the aircraft fuel system. The refueling probe extension and retraction system shown in figure 12-62 consists of the refueling probe, refueling nozzle, a self-locking, two-position probe actuating cylinder, a lock swivel joint, two restrictor valves, a selector valve, and associated electrical switches and relays.

With the engines operating or external electrical and hydraulic power applied, the probe is extended by placing the refueling probe switch in the EXTEND position. This electrically actuates the solenoid selector valve to supply restricted hydraulic flow to the extend port of the probe-actuating cylinder. The restrictor valves control the rate of cylinder extension and retraction. The check valve prevents pressure surges in the hydraulic return system from unlocking the probe-actuating cylinder during flight.

After disengaging the probe nozzle from the tanker drogue, hold the air refueling switch in RETRACT to actuate the solenoid selector valve to supply pressure to the retract port of the probe actuating cylinder, causing it to retract and lock the probe into place. A cockpit advisory panel transit light goes out whenever the probe is locked in the extended or retracted position. A probe floodlight, which illuminates the probe tip for visual contact with the refueling drogue at night, is on whenever the refueling probe switch is in EXTEND and exterior lights are on. The floodlight goes out when the refueling probe switch is placed in RETRACT or OFF. Organizational maintenance of the air refueling probe system normally consists of operational checks, troubleshooting, rigging and adjusting, and removal and installation of components.

To perform an operational check of the air refueling probe system, the hydraulic system must be pressurized to 3,000 psi, external electrical power applied, and the in-flight refueling circuit breaker engaged. Before actuating the system, ensure that all personnel and equipment are clear of the area of probe travel. The extension cycle rotates the probe from its stored locked position to an extend locked position.

Position the fuel probe switch to EXTEND. Check for proper probe extension and probe locking. If operation of the probe is not smooth, check for air in the system. Position the fuel probe switch to RETRACT and check for proper probe retraction. The complete extension cycle should be from 5 to 7 seconds, with the retraction cycle taking from 9 to 11 seconds. Troubleshooting of the system should include a thorough knowledge of the malfunction compared to proper system operation and referral to system schematics and troubleshooting tables provided in the MIM. System rigging, component removal and installation, and all other maintenance should be in accordance with the procedures and safety precautions outlined in the MIM.

Intermediate maintenance of faulty components consists of cure-date kit installation and testing in accordance with the "Intermediate Maintenance" section of the MIM or the applicable (03) overhaul manual.