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. WING FOLD SYSTEMS There are miscellaneous differences in the design and operating characteristics of the various hydraulically operated systems, and the wing fold systems are no exception. Basically similar components perform similar functions with only minor variation in part nomenclature and physical design. The wing fold system described in the following paragraphs will point out some of these differences. Refer to the wing fold system schematic shown in figure 12-63 as you read the following paragraphs. The wings arc unlocked by lifting the wing fold handle up and forward until it reaches the first stop. This action operates the cable and pushrod mechanisms that control mechanical locking of the wing lock cylinders. This same action, through the pushrod connected to the mechanical locks, causes the warning flags to appear on top of the wings. Further movement of the wing fold handle at this point is prevented by a spring-loaded mechanical latch that blocks the crank at the wing lock cylinder. With flight controls in the proper position and weight on the wheels, the wing fold lockpin switch is placed at UNLOCK. Power is supplied to the unlock side of the wing lock selector valve, allowing combined system utility hydraulic pressure to the four wing lock cylinders in each wing. Pressure in the wing lock cylinders moves the lock shaft to retract the wing lockpins. After completion of this action, the wing fold control handle can be moved to the full forward position, operating the wing fold selector valve in each wing and porting hydraulic pressure through flow regulators to the wing fold actuating cylinders, which extend and cause the wing to fold. The wings are spread by moving the wing fold control handle aft to the first stop, mechanically positioning the wing fold selector valve in each wing to port hydraulic pressure through flow regulators to the wing fold cylinders, causing them to retract and spread the wings. The wing fold control handle is held at the first stop by the retracted lockpins, rotation of the lock shafts and cranks. which prevent 12-71