The Retraction cycle
Once the aircraft is airborne, the pilot may select the GEAR selector switch to the ‘UP’ position at any time the aircraft is below 180 KIAS.
This will energise the bypass valve to block flow to the hydraulic reservoir (HYD PRESS ON light illuminated) and energise the gear control valve to allow hydraulic pressure to the internal down lock mechanisms in the gear actuators.
Hydraulic pressure is then applied to the retraction side of the hydraulic actuators and the landing gear will be drawn up in to the respective wheel wells where they will be locked in the up position by the spring loaded mechanical up locks.
Once the landing gear down locks are unlocked the GEAR UNLOCKED light will illuminate until the up locks micro switches are made with the gear up and locked.
The gear doors will be mechanically drawn with the landing gear legs as they move to complete the retraction cycle.
Once the retraction cycle has completed, the bypass valve will re-open and allow hydraulic fluid to be routed back to the reservoir returning the hydraulic system to the ‘open centre’ condition (HYD PRESS ON light goes out).