Landing Gear Description And Operation; Landing Gear Troubleshooting - Piper PA-44-180 SEMINOLE Maintenance Manual

GENERAL.
This chapter consists of instructions for the overhaul, inspection and adjustment of the various components of
the landing gear and brake system, including adjustment of the electrical limit, safety and warning switches. This
chapter does not cover the hydraulic function of the landing gear retracting system. (Refer to Chapter 29.)
DESCRIPTION AND OPERATION.
The airplane is equipped with retractable, tricycle air-oil strut type landing gear which are hydraulically
operated by an electrically powered reversible pump.
Gear positions are indicated by three Three lights located above or below the selector lever for gear down and
locked, and a red light located at the top of the instrument panel(pilot's side) for gear unsafe positions. There is
no light to indicate that the gear has fully retracted other than all lights are out. As the landing gear swings to the
down and locked position and each downlock hook moves into its locked position, a switch at each hook actuates
to the switch normally closed (NC) circuit to indicate by a Three light that the individual gear is safely down and
locked. The activation of all three downlock switches will also shut the hydraulic pump off. As the instrument
lights are turned on, the green lights will dim. When the gear begins to retract and the downlock hooks
disengage, the down limit switches actuate to the NC circuit and in series with the NC circuit of the up limit
switch allows the gear unsafe light to come on. The gear unsafe light will remain on until the gear is up and all
up limit switches are actuated to their normally open (NO) circuit.
Each landing gear is retracted and extended by a single hydraulic cylinder attached to the drag link assembly of
the nose gear and the side brace link assembly of the main gears. Gear doors partially enclose the gear and
operate through mechanical linkage with each gear. The gears are held in their up position by hydraulic pressure
alone within the cylinders. There are no uplocks and loss of hydraulic pressure will allow the gears to drop. It is
preferred that the gears be extended and retracted with the use of the gear selector handle; however in the event of
hydraulic loss or electrical failure, they can be lowered by pulling on the emergency extension knob which will
open a valve between the two hydraulic lines to the nose gear cylinder thus allowing hydraulic pressure to
neutralize between each side of the cylinder pistons and allowing the gear to free fan to the downlocked position.
To assist the nose gear to extend under these conditions are two springs, one inside the other, mounted on arms
above the gear links. The main gears require no assist springs. Once the gears are down and the downlock hooks
engage, a spring maintains each hook in the locked position until hydraulic pressure again releases it. A further
description of the hydraulic system may be found in Chapter 29.
The nose gear is steerable through a 60 degree arc by the use of the rudder pedals. As the gear retracts,
however, the steering linkage becomes separated from the gear so that rudder pedal action with the gear retracted
is not impeded by the nose gear operation. A shimmy dampener is also incorporated in the nose wheel steering
mechanism. A single bungee spring unit is incorporated between the rudder pedals and nose gear.
The two main wheels are equipped with self-adjusting single disc hydraulic brake assemblies. Hydraulic fluid
for the brake cylinders is supplied by a reservoir installed at fuselage station 49.50.
TROUBLESHOOTING.
Mechanical and electrical switch troubles peculiar to the landing gear system are listed in Chart 3201. When
troubleshooting, first eliminate hydraulic malfunctions, then proceed to switch malfunctions and last to the
mechanical operation of the gear itself. Always place the airplane on jacks before attempting any troubleshooting
of the gear.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2F17
3 2 - 0 2 - 0 0
Page 32-01
Revised: May 15, 1989