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Gravity Extension
A gravity extension is required in the case of:
- green system failure;
- after a blue system and yellow system (double hydraulic) failure;
- in ELEC EMER config with hydraulics supplied by the engine driven pump (EDP); or
- sometimes after a dual LGCIU failure.
The landing gear actuators have a large fluid capacity and so use of the green system in cases 2. and 3. above would cause low system pressure and cavitation in the flight controls. Therefore the priority valve closes requiring a gravity extension.
The gear doors remain open after a gravity extension, and so nose wheel steering is lost.
Controls
| DOWN | landing gear is isolated from the green hydraulic system and doors and gear are electrically unlocked |
| RESET | system is set back to normal extension and retraction mode |
| OFF | normal operation |