Concorde Landing Gear Operation
Landing Gear Retraction and Extension
Retraction and normal extension is electrically signaled and hydraulically actuated. The landing gear up selection initiates a sequence of actions. If the up-locks are open and ready, the doors for the three principal gears are opened, then if nose wheel steering is centered and main bogies level, hydraulic pressure opens the down-locks, unlocks the shortening mechanism and retracts the gear. When up-locks are engaged, the doors will close. Extension is far simpler: its checks that the down-locks are open then sequences doors open, gear down and door close. Tail gear basically followers the others, but is not involved in sequencing. Maximum speed for gear operation is 270kts; it takes about 12 second to retract.
When the landing gear lever on the flight deck is in the NAUTRAL position, both the electrical control and hydraulic supply are shut off leaving the doors held by the mechanical locks, thus preventing inadvertent land gear extension through control or actuator failure. During the landing gear retraction the main and nose wheels are automatically braked and released.
In the event of hydraulic malfunction there is a standby lowering system. It is accomplished hydro-mechanically and by manual sequencing and timing, by means of a separate control lever on the Centre Pedestal Instrument Panel on the flight deck, the lever is independently powered by the Yellow hydraulic system.
FREE FALL OPERATION
Certain combinations of problems would plan to preserve the hydraulic effort exclusively for the flight controls. In these cases the landing gear would be lowered by free-fall mechanisms. This involves a visit to the passenger cabin and opening a floor panel. Free-fall controls are located immediately above the nose gear and the main-gear up-locks. For the nose-gear a rotary control first isolates hydraulics and vents the retraction jack to atmosphere, then via a screw jack mechanism opens the doors up-locks and the gear up-locks. The gear falls into the doors pushing them open, the airstream catches the gear and pushes it into the down-lock.
Under the rear cabin floor a rotary control does the similar job on the main landing gear hydraulics, but this time a cranked lever is placed into a socket and, from a kneeling position with body braced and trying not to grimace it is heaved forcefully to starboard to open the up-locks.
In both cases a change in slipstream noise will indicate the measure of success. A practiced hand will achieve ‘3 green’ within 2 minutes and 45 seconds. At this point the tail gear would remain in the up position.
To assist in locating the free fall controls, a starboard hat rack in both forward and rear cabins is identified with 1 red and 1 green disc at a position adjacent to each control panel.