Hydraulic Leak on Approach with a Gear Unsafe Indication
You are on approach at 1,200 ft AGL in a retractable-gear light twin (MTOW 5,200 lb) with a 1,500 psi hydraulic system: an engine-driven pump on the left engine, an electric auxiliary pump used for gear and flap selection, and a reservoir visible through a sight glass. Selecting gear DOWN gives three greens, then the right main green goes out and the red gear-unsafe light and horn come on with the throttles retarded. System pressure has fallen from 1,500 to 1,100 psi and is still dropping; the auxiliary pump runs but cannot hold more than 600 psi. The reservoir is at the LOW mark and falling, and there is fresh hydraulic fluid streaking along the left engine nacelle and the inboard section of the left flap. You have 90 minutes of fuel. The weather is VMC, 8 km visibility, wind 090/12 kt, runway 2,400 m.
1. Explain what has failed and why continuing to cycle the gear or run the pump is a bad idea.
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Falling pressure with a falling reservoir and fluid outside the aeroplane means fluid is being lost, not that the pump has failed. The leak is on the left side, upstream of the gear and flap actuators, which explains the streaks under the left nacelle and flap. The auxiliary pump cannot hold pressure because it is pumping fluid overboard. Every additional gear or flap cycle pumps more fluid out and, worse, deposits fluid on hot exhaust and turbo areas, which is a fire risk. The electric pump also overheats and its circuit breaker may pop, which could leave nothing available for a later attempt. The right main showed green and then went out after the leak started, so its actuator may have bled down or the down-lock may not have engaged. I would stop cycling, select the pump off and go straight to the emergency extension.
2. Describe the landing configuration and approach you would fly, and why.
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The emergency system extends the gear mechanically (spring or gas charge), so I would pull the emergency gear handle as the AFM requires, hold it as directed, and then check three greens plus any mechanical down-lock indicators on the wings. Flaps are hydraulic too, so I would expect them to be inoperative or, worse, to extend asymmetrically; I would plan a flapless landing. That means an approach speed of roughly Vref plus 10 to 15 kt, a flatter power-on approach, a longer flare and a touchdown about a third of the way down a 2,400 m runway using the whole length. I would brief the no-flap go-around, keep the gear down after extension, and finish the normal drills: harnesses, doors, and fuel and master off on touchdown if there is a fire risk.
3. What would you do if the right main still shows unsafe after the emergency extension, and what precautions on touchdown?
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I would ask the tower for a low pass at about 200 ft so they can visually confirm whether the right leg is down and locked, and ask for the fire service to be standing by. If it is confirmed down, I would land with the left main touching first, holding the right wing off as long as possible and lowering it gently so the load comes onto the right leg slowly. If it is not down, expect the right wing to drop: keep the speed up to touchdown, hold the centreline with rudder and asymmetric braking, shut down both engines and the master switch and get out. With 90 minutes of fuel there is no reason to rush, and a controlled landing is safer than a hurried one.