Troubleshooting steps provided in the MIM are
full open position when the landing gear control handle
normally aligned with the sequence of events or steps in
is placed in the UP position. Placing the landing gear
the operational checkouts. They provide an efficient
control handle momentarily to the UP and DOWN
means of isolating the malfunction. The MIM requires
positions several times will correct this condition by
that each step in the operational checkouts be
removing air from the wheel door cylinders.
performed in sequence. If trouble occurs during the
Regulate the hydraulic test stand to operate at a
procedure, it must be corrected before proceeding with
flow of 4 gpm, (gallons per minute) and slowly increase
the next step. These troubleshooting aids provide a
hydraulic pressure. The landing gear down lockpins
logical cause for many anticipated landing gear
should start to retract. They should be fully retracted
malfunctions, including procedures for isolating and
when the pressure reaches 1,800 psi, and then all gear
remedying the problem. Refer to the system schematic
assemblies should start to retract.
for the particular system and accompanying
When the nose gear nears the up position, be sure
maintenance instructions, in addition to sound
the fairing doors are cammed to the closed position, and
reasoning, to pinpoint the cause for a malfunction in an
then check all gear doors to be sure they are closed and
efficient manner.
locked when the position indicator indicates the
Some landing gear malfunctions are related to
up-and-locked condition. Move the landing gear handle
improper maintenance practices, with the lack of
down and check to see that the wheel fairing doors open
proper lubrication being the predominant malpractice.
and gear assemblies extend. Visually check all gear
A review of past discrepancies and previous corrective
assemblies to ensure they are down and locked. With
actions may also aid in analyzing malfunctions.
the test stand regulated to 3 gpm at 3,000 psi, the gear
Occasionally, discrepancies that are reported as a
should make a complete cycle (up and down) in 12 to 14
result of flight are difficult or even impossible to
seconds. The maximum pressure required to retract and
duplicate on the deck. However, too many
lock the gear is 1,800 psi at 4 gpm.
discrepancies signed off with "Could not duplicate
When you check the emergency extension of the
system checks 4.0," or similar corrective actions, show
gear, first retract the gear normally, secure external
up as repeat malfunctions or as the cause of accidents.
hydraulic pressure, place the landing gear handle in the
Every effort should be made to locate a sound logical
down position, and then pull and hold the emergency
cause for a reported malfunction by thoroughly
extension handle fully aft. Visually check that all gear
checking the system, each component, linkages,
assemblies are down and locked by observing the
clearance, and associated indicating systems. All
landing gear position indicator in the cockpit, and then
phases of the operational checkouts must be verified by
release the emergency extension handle. It may be
a quality assurance inspector.
necessary to manually push the gear assemblies to the
Detecting internal leakage of components may
down-and-locked position. The force required to push
require the use of special equipment, such as the
the main gear to the locked position should not exceed
ultrasonic leak detection translator or simple isolation
20 pounds applied to the axle hub. The force required to
of components by disconnecting lines, applying
push the nose gear to the locked position should not
pressure, and measuring for allowable leakage limits.
exceed 10 pounds applied at the center line of the axle
hub. Make at least one complete normal cycle of the
ALIGNMENT AND ADJUSTMENT
landing gear, and then remove external power and
aircraft from jacks.
Improper rigging or adjustment of landing gear
NOTE: Some aircraft require resetting of the
linkages results in a significant number of unsafe or
landing gear dump valves before recycling the landing
hung landing gear discrepancies. Most landing gear,
gear. Refer to the applicable MIMs.
when in an overcenter and locked position (up or
down), requires very little interference or binding to
TROUBLESHOOTING
prevent its initial movement.
Alignment of newly installed landing gear
Troubleshooting of the landing gear system, like all
assemblies or individual components should be in strict
hydraulic systems, requires that you understand the
accordance with the procedures outlined in the
theory of operation of the particular system and the
applicable MIM. Complete assemblies are aligned in a
function and sequence of operation for each com-
specified sequence, with designated steps throughout
ponent.
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