mechanism, shown in figure 12-5, are a hydraulic latch
cylinder, a latch hook, a spring-loaded linkage, and a
sector. The latch cylinder is connected hydraulically
with the landing gear control system and mechanically,
through linkage, with the latch hook. When hydraulic
pressure is applied, the cylinder operates the linkage to
engage or disengage the hook with or from the latch
roller on the door. In the gear down sequence, the hook
is disengaged by the spring load on the linkage. In the
gear up sequence, spring action is reversed when the
closing door is in contact with the latch hook, and the
cylinder operates the linkage to engage the hook with
the latch roller. Cables on the landing gear emergency
extension system are connected to the sector to permit
emergency release of the latch rollers. An up lock switch
is installed on, and actuated by, each latch to provide
main-gear-up indication in the cockpit.
With the gear up and the door latched, inspect the
latch roller for proper clearance. See view B of figure
12-6. On this installation, the required clearance is
1/8 inch ±3/32 inch. If the roller is not within tolerance,
it may be adjusted by loosening its mounting bolts and
raising or lowering the latch roller support. This can be
done because of the elongated holes and serrated locking
surfaces of the latch roller support and serrated plate.
See view A of figure 12-6.
Figure 12-6.–Landing gear door latch installation.
LANDING GEAR DOORS
When installing new landing gear doors, you have
to trim each door for a specific installation to obtain the
required clearances. The amount of material to be
trimmed is determined by retracting the landing gear
(with the door linkage disconnected), and then releasing
the hydraulic pressure. The up lock rollers on the doors
are then removed to allow the doors to be closed, and
yet not become locked in the closed position. With the
landing gear doors held in the closed position, each
door’s edge is marked where trimming is needed to
maintain the specified clearances. The doors are then
opened and the excess amount of material trimmed off.
After you have completed the trimming and checked the
doors for proper clearances, the landing gear is lowered
and the door linkage and up lock rollers are installed.
The distance the landing gear doors open or close
depends upon the length of door linkage and adjustment
of doorstops. Maintenance instruction manuals (MIMs)
specify the length of door linkages and adjustment of
stops or other procedures whereby correct adjustments
may be made. On some models of aircraft that
incorporate forward and aft landing gear doors, the
doors are adjusted separately, and in some cases, they
are “pulled” or “warped” into a desired shape.
12-7
