AIR TRACTOR AT-502A, Секция обслуживания

Страница: 25 / 159

Maintenance Page 6 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
a pin punch. The lower bushing has a chamfered end which is positioned on the lower extreme of the
housing at the brass wear plate. The housing assembly is p/n 40089-1 which is less bushings, wear plate,
and attaching hardware and grease fitting.
Tail Wheel Lock Pin and Housing
The lock pin housing is p/n 40025-1 and attaches to the steel plate on the lower end of the fork housing with
four countersunk screws. The four holes in the base of the lock pin housing are oversize to allow adjustment
of the locking pin. If the aircraft tends to steer to the left or to the right on the ground with the lock pin
engaged, it is necessary to re-position the lock pin housing. Jack the tail wheel clear of the ground, lift the
lock pin up and swivel the fork to one side so that the four screw heads are exposed. Make a pencil mark
along the edge of the lock pin housing plate for a reference and estimate the amount of movement for the
lock pin housing. Loosen the 4 screws and move the housing the desired direction. Swivel the fork back into
position and allow the locking pin to engage the fork, then tighten the two outboard screws. Then rotate the
fork back so that the two inboard screws can be tightened. Check the lock pin again to see that it freely
engages the fork. Taxi the aircraft in a no-wind condition or if there is a light wind, taxi both up-wind and
down-wind with the rudder pedals in the neutral position and the stick back so that you are sure the lock pin
is engaged. Keep adjusting the locking pin housing until the aircraft will taxi in a straight line.
During annual inspections (or more frequently if required) remove the housing and slide out the locking
pin to check it for wear and straightness. The compression spring inside the housing should also be checked
for broken coils. The locking pin is p/n 40021-1 and the spring is p/n 40026-1. If the lock pin bushing in the
striker plate becomes worn, replace it using the Service Letter #171 lock pin bushing kit.
MAIN AND TAIL GEAR ATTACH BOLTS
The bolts attaching the main and tail gear springs to the fuselage structure are among the most
important structural components of the aircraft. Being structural components under constant stress, these
bolts have definite fatigue lives. The predictability of the fatigue life of each bolt is impossible due to the wide
variety of operating conditions that include smoothness of landing strips, number of landings per hour, pilot
landing technique, load carried, the way the turns on the ground are made, the way the brakes are used, and
many other small but significant factors. Dropping in over the trees and hitting the ground during a spray run
may not cause a gear bolt failure, but the effect on the fatigue life of the bolt could be the same as several
thousand landings on a rough strip. A bolt that is not tightened to the proper torque, especially when there is
visible clearance between the gear spring and the fuselage, will last only a fraction of the time normally
expected.
We have seen paved-landing strips that had big potholes impossible to miss when landing that must
impose huge loads on the forward main gear clamp bolts. How many times do you hit the potholes before
the bolts break? Some strips are so rough you woul
dn’t dare drive your empty pickup over 30 mph down the
strip, yet there goes an Air Tractor with a ton of fertilizer bouncing along at 80 mph on a still day just before
lift-off. Lie down on the ground and look at the massive structure supporting all four wheels of your pickup.
Now look at your Air Tractor gear support, and consider the leverage that exists between the gear leg length,
and the distance between the clamp block bolts.
What we are trying to tell you is that your aircraft is not a tank. The gear will support a surprising
amount of load, the bolts will take a lot of tough licks, but don’t press your luck and think that they will last
forever without breaking.
Accordingly, we have established what we feel is a conservative, yet realistic time period for gear bolt
changes, based on field experience at this time. The bolt life shown is based on normal operations, and if