C90 Hydraulics / Gear

Question 1

Nose Wheel Steering

POH 7-19

Answer 1

Ground control is achieved by interconnected Nose Wheel Steering, actuated via the rudder pedals

A spring loaded link absorbs all rudder inputs on the ground when stationary to minimise nose wheel forces and scuffing until the aircraft is moving, at which time steering input forces will become reduced.

A self catering cam centres the nose wheel during the retraction cycle and prevents nose wheel movement yet full rudder travel when retracted

Direct linkage to the rudder pedals allows the nose wheel to be turned through 14° to the left of centre and 12° to the right.

When rudder control is augmented by the brake, the nose wheel can be deflected up to 48° to either side of centre.

Question 2

Landing Gear

POH 7-20

Answer 2

Conventional Tricycle landing gear system

Operated by 28VDC Hydraulic Pack

This landing gear is electrically activated and hydraulically actuated.

Question 3

Gear Selector

Answer 3

Squat switches are located on the Main Gear knees to provide
inadvertent retraction protection
air-ground logic
Squat switches also connect to the Down Lock solenoid to prevent lever movement on ground. Down Lock override release also provide for Non Normal use.

Question 4

Gear Extension

Answer 4

Selected down on the Gear Control Lever will activate the Hydraulic Power Pack and pressurise the down side of the extension cylinders.

Hydraulic Pressure pushed the gear legs through “over centre” position on Over Centre Cams locking the gear down. Simultaneously, at full travel, the Down Lock switches will be activated interrupting power supply to the Hydraulic pump.

This will also trigger the Green Down position indications and extinguish the red Transit indications on the Gear Position Indicator

Question 5

Gear Retraction

Answer 5

After the squat switch safety relay is closed by weight off wheels, selected the Gear Control Leaver to UP will pressurise the up side of the gear extension cylinders.

The power pack will continue to pressurise the system until 1850 PSI is reached, at which time the Gear Up Pressure Switch will be activated. The system pressure hold the gear in the up position.

If pressure falls below 1600 PSI , the pump will reenergise to provide system up lock pressure.

Question 6

Alternate Gear Extension

POH 3A-9 Abnormal procedures

Answer 6

Alternate Gear Extension is achieved by positioning the system control valves to the normal Gear Control Leaver to the Down position

System pressure is then accumulated via a manual hand pump located in the aircraft cockpit. Pumping is continued until the normal Green gear down indications are illuminated.

Care must be taken when pumping so as not to push the hand pump through its securing clip position as this will dump accumulated pressure and pressurisation will have restarted.

Question 7

Gear Warning System

Answer 7

Flaps in UP or APPROACH position and either or both power levers retarded below a certain power lever will see the Gear warning horn will sound and the red gear handle Transit light illuminate

GEAR WARN SILENCE is on the left power lever. The system will re-arm when the power levers are advanced

FLAPS set beyond the APP position will see the warning horn and landing gear handle light will be activated regardless of the power setting and neither can be cancelled.

Question 8

Brakes

POH 7-24

Answer 8

Toe brakes through the rudder pedals activates a Puck and Disk braking mechanism on each Main Gear hub.

Pilot’s and Co Pilot’s toe brakes can pressurise the park brake, this is achieved by pressurising the systems then selecting the Park Brake Lever out. This will select the brake line isolation shuttle valves to closed, retaining system pressure