You can do away with the pump, pipes, and power supply. Since the main propulsion isn't going, closed hydraulics would have to have an independent power supply

You can do away with the pump, pipes, and power supply. Since the main propulsion isn't going, closed hydraulics would have to have an independent power supply. Probably batteries. Instead, they replace all that with some compressed air. They can run out of compressed air, but can also run out of whatever powers the pumps in a closed system. The hydraulic fluid is probably RP-1 and is probably dumped into the fuel tank, where it's available for later burning. Another 2-for-1.