HYDRAULICS - BLOCK DIAGRAM
Continental
Rev. 12/01/00 #29 Flight Manual

HYDRAULICS - CONTROLS AND INDICATORS
Temporary Revision Sec. 14 Page 5 MD-80 Rev. 01-02  05/30/01 Continental Flight Manual Sec. 14 Page 6

MD-80
Continental
Rev. 12/01/00 #29 Flight Manual
INTENTIONALLY LEFT BLANK

LANDING GEAR

General
The airplane has a tricycle landing gear that is mechanically actuated and hydraulically operated. Normally, actuated by a landing gear handle, the gear may be raised or lowered by pressure from the right hydraulic system or by pressure transferred from the left hydraulic system through the power transfer unit. When retracted, the gear is fully enclosed by doors. If the right hydraulic system fails, the gear can be mechanically released to free-fall to the extended and locked position. Dual, hydraulic-powered multi-disc wheel brakes with anti-skid control systems are provided on the main gear. An electrically monitored visual/aural/vocal indicating and warning system provides indication of gear and brake system status.
Spray deflectors on both main gear and nose gear assemblies serve to minimize water and slush ingestion on takeoff and landing.
A tail bumper assembly, mounted on the bottom of the aft fuselage, prevents structural damage if the aft fuselage should make contact with the ground.
Nose Gear
The nose gear assembly consists of dual wheels mounted on a steerable shock strut. The nose gear assembly is locked in both the extended and retracted positions by overcenter linkage. During normal operation, the overcenter linkage is released hydraulically to permit gear extension and retraction. If hydraulic pressure is not available, the overcenter links may be released by the emergency gear extension lever.
A ground shift mechanism, mounted on the nose gear strut, is operated by the compression and extension of the nose gear strut. When the strut is not compressed, the ground shift mechanism disengages the rudder pedal nosewheel steering mechanism, centers the nosewheel for retraction, and retracts the landing gear handle release button. The ground shift mechanism also actuates two ground control switches that establish ground or flight modes of operation.
Nose Gear Doors
The nose gear wheel well enclosure consists of two forward and two aft doors. The doors are mechanically operated by movement of the nose gear during retraction and extension. The forward doors are closed when the gear is extended but may be opened for ground maintenance operations.
Continental
Rev. 12/01/00 #29 Flight Manual
Nose Wheel Steering
Nosewheel steering is hydraulically actuated and mechanically controlled by a steering wheel or rudder pedals. The steering wheel is the primary control used to maneuver the airplane at normal taxi speeds and provides 82. of turning angle in either direction. The rudder pedals are used to steer the aircraft at high speeds during takeoff and landing, and provide 17. of turning angle in either direction.
The nosewheel steering system consists of two independent control valves and actuating cylinders that are supplied hydraulic pressure from separate sources. The left steering cylinder receives pressure from the left hydraulic system; the right cylinder is supplied by the right system. Nosewheel steering, with only one hydraulic system operating, will function normally except for a reduction in maximum steering angle.
While the steering system is in the neutral position, the cylinders function as shimmy dampers. A manually operated bypass valve is actuated prior to towing the airplane, which deactivates the steering system permitting manual movement of the nose gear strut.
Main Gear
The airplane has two main gear assemblies consisting of dual wheels mounted on a shock strut. When extended, each main gear assembly is locked in the extended position by overcenter linkage. When retracted, the main gear assemblies will be held up by hydraulic pressure providing the engine driven hydraulic pumps are selected to provide 3000 psi. If the pumps are selected to provide 1500 psi, the main gear will rest upon the doors. If hydraulic pressure is not available for gear extension, the main gear door latches may be released by the emergency gear extension lever.
Main Gear Doors
Each main gear wheel well enclosure consists of a hydraulically operated main gear door and a mechanically operated outboard door. The main gear doors are mechanically latched when closed and support the main gear during flight. The main gear doors cycle to the closed position after the main gear approaches the fully extended position. The main gear doors may also be mechanically released and opened on the ground.
Visual / Aural Indicating and Warning System
Landing gear position and main landing gear door status is indicated by gear lights on the upper instrument panel. Landing gear position lights illuminate green to indicate that the landing gear and landing gear handle are in the down-and-locked position. The lights illuminate red when the landing gear is in any intermediate position between up-and-locked and down-and-locked or individually, when the associated landing gear assembly is not in the position that corresponds to the position of the gear handle and either one or both throttles are less than one-half inch from the idle stop position. The GEAR DOOR OPEN light will illuminate any time either one or both main gear doors are not closed.
　
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