AIR TRACTOR AT-502A, Maintenance Section

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Maintenance Page 18 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
The actuator assembly has a threaded collar. This collar is threaded internally to match the threads on
the worm drive threads of the actuator, and is threaded externally to match the threads of the Air Tractor
“Tee” assembly which is p/n 70037-1. The “Tee” assembly is attached to the two 1/4" aluminum 70032-1 arm
assemblies that are bolted to the flap torque tube assembly. The “Tee” assembly has a steel grease shield
and cap attached. The shield is p/n 70039-
1 and is attached to the “T” with two AN500A5-3 screws. The cap
is a 1 1/8 SC Caplug attached to the shield with a TY-525 Tyrap.
The “Tee” assembly that screws into the Threaded collar has a AN565D6H4 set screw that is located
on th
e top surface of the “Tee”. The threaded collar has a large diameter rounded surface and just forward is
a smaller diameter part on the collar that is to be used for tightening the collar against the “Tee”. Whenever it
is necessary to remove the flap actua
tor, the factory practice is to first loosen the set screw in the “T”
assembly with a small Allen wrench, then place a soft rag or duct tape on the small diameter of the threaded
collar so as not to scratch the finish and with a pair of water-pump pliers or vise-grips, break loose the
connection between the threaded collar and the “Tee” assembly. Then the threaded collar can be screwed
by hand from the “Tee”. CAUTION: Have someone hold up on the flap trailing edge so the flaps will not fall
down against the boom hangers.
See the section "Flap Actuator Troubles
hooting” for a step by step procedure for removing the actuator
assembly from the aircraft.
Entrance inside the fuselage is made easier by removing the lower R/H pulley next to the header tank
so that the rudder interconnect cable will not be in the way, and entering the fuselage from the R/H side.
Remember that there is a washer under the pulley when it is re-installed.
All wires from the flap actuator assembly have Wristlock connections so that it is not necessary to cut
or splice wires when the actuator is removed. Also, it is possible to replace the motor without removing the
actuator assembly.
Flap Actuator Troubleshooting
If any trouble develops, first check the flap circuit breaker on the panel. If this does not produce any
results, a visual inspection of the micro-switches and micro-switch arms should be made. Enter the fuselage
as described before and inspect the micro-switches for broken actuator arms or loose wires.
If the flaps are up but won
’t go down, chances are there is something wrong with the
down relay. If the
flaps are down but won’t go up, look for trouble with the
up relay. If it is necessary to keep flying and make
repairs later, the flaps can be retracted by rotating by hand the rudder coupling at the motor shaft. This is
slow, but the flaps can be raised this way.
If the flap goes down past the 26
o
mark, check the down micro-switch. Have someone cycle the flaps
and see if the roller on the micro-switch arm lifts properly on the striker plate and pushes in the micro-switch
plunger to stop the travel. If there is any doubt, push the plunger in with the flap midway through the stroke. If
the switch is working, the flap will stop. In this case, the down micro-switch needs to be re-positioned to
activate the micro-switch.
Check the micro-
switches with an Ohmmeter. Check continuity between the “C” pin and the “N.C.” pin
on both switches. Activate the switch by pushing the plunger in and check continuity between the “C” pin and
the “N.O.” pin. If these checks are positive, the micro-switches are OK and do not need to be changed. If a
switch is bad, change it.