flap and spoiler systems are hydraulically operated. On aircraft 25-061 through 25-180 the engine driven hydraulic pumps supply fluid under pressure of 1500 psi to the system pressure is maintained at 1250 to 1500 psi by a pressure regulator. On aircraft 25-181 and subsequent the variable volume engine driven pump delivers fluid under a pressure of 1450 psi to the system and static pressure is maintained at 1500 to 1550 psi. Over pressurization is prevented by a pressure relief valve which opens at 1700 psi. A pre-charged accumulator dampens and absorbs pressure surges. Two motor-driven shutoff valves will stop hydraulic flow to the engine-driven pumps in case of an emergency. The valves are controlled by the FIRE switch and activation of these valves are indicated with pinhead lights located in the cockpit next to the FIRE switch. On aircraft equipped with an auxiliary hydraulic pump, the hydraulic pump switch located at the lower centre of the instrument panel activates the auxiliary hydraulic pump to provide in-flight standby hydraulic pressure. A pressure switch will energize the pump if hydraulic pressure falls below a preset level and de-energize the pump when pressure returns to normal. A duty cycle of 3 minutes on and a cooling period of 20 minutes off is required to avoid overheating the pump motor. Landing gear The hydraulically retractable landing gear is of conventional tricycle configuration with air-hydraulic shock-type nose and main gear. The main gear has dual wheels and brakes on each strut. The brake system incorporates four power-boosted disc-type brakes with integral anti-skid system. The nose wheel has a specially moulded tire to prevent water splashing into the engines. Nose wheel steering is electronically controlled by the rudder pedals, utilizing the synchro principle. Hydraulic pressure for retraction and extension of the gear is transmitted by a system of tubing, hoses and actuating cylinders and is electrically controlled by limit switches and solenoid valves. Emergency extension can be accomplished pneumatically in case of hydraulic or electrical system failure. The main gear is enclosed by two doors after retraction. The inboard doors are hydraulically operated while the outboard doors are mechanically operated by linkage connected to the main gear struts. The nose gear doors operate mechanically with linkages attached to the nose gear shock strut. Brakes The Learjet 25 utilize wheel brakes as the primary method for reducing speed after landing. The brake system utilizes hydraulic pressure for