Extension And Retraction - Piper Cheyenne IIIA Airplane Maintenance Manual

PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCE MANUAL
A. Extension and Retraction
(1) Description and Operation
The nose gear retracts aft into the nose section, pulling mechanically interconnected gear doors
closed. The main landing gears retract inboard into each wing and are covered by hydraulically
actuated doors and those mechanically connected to each gear.
The gear operating mechanisms use two systems. The primary system uses hydraulic power
during normal operations and is covered in Chapter 29. A secondary or redundant system,
incorporated into each gear operating mechanism, provides a way of extending the required gear if
any part of the hydraulic system fails. The secondary system, incorporated as an emergency
backup for the hydraulic system, only moves the affected gear to the down position.
The landing gear operating controls are located on the pilot's side of the instrument panel. The
gear selector, with the indicator lights to its right, is situated on the bottom of the panel directly
under the column of engine instruments. The emergency extension button is also mounted on the
pilot's side of the instrument panel, just below the oxygen pressure gauge, to the right of the
alternate static source selector.
Two means of emergency extension are available. The emergency extension (blowdown) system
(EES) (refer to 32-30-00 Figure 1) employs a logic circuit which senses gears not extended.
When the button is pushed, the remaining gears are extended and locked in place. The system
works so if one or more gears fail to extend and the emergency extension button is pushed, the
logic relay allows electrical power to ignite an explosive charge on the affected gear's system.
After the charge is blown, compressed dry nitrogen is released through its own system of tubing
and into the working actuators. Each individual system uses a gas supply bottle, shuttle valve, and
up lock-unlocking actuator, all of which are gas operated.
Besides the emergency blowdown system, the gear can also be pumped down. A hand pump
found under a floor access panel between the pilot's and copilot's seat can be used to extend the
gear if the hydraulic pump system fails. If a problem does develop, and time permits, use the hand
pump first because once the emergency extension system is activated, the affected mechanism
and hydraulic system must be purged and serviced.
An anti-retraction system is installed to guard against inadvertent retraction of the landing gear
when the airplane is on the ground, a solenoid latch is positioned just above the control lever. A
squat switch on the landing gear and a dynamic pressure q sensor must operate this latch before
the landing gear selector control can be moved upward. The landing gear control knob is in the
shape of a wheel to differentiate it from the flap control, which has a knob in the shaft of an airfoil.
EFFECTIVITY:
040-999
32-30-00
Jan 10/90