AIR TRACTOR AT-502A, Секция обслуживания

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Maintenance Page 2 Air Tractor, Inc.
March 14, 2018 AT-502A502B/504
If the tail spring is to be removed or checked for looseness, or have bolts changed, place the small
hydraulic jack under the point of the L/H stabilizer strut attach fitting that welds to the lower fuselage
longeron. Again, be sure the parking brake is set before jacking.
If the main gear springs are to be checked for looseness, or bolts changed (other than the forward
clamp bolt), the aircraft must be lifted with a hoist, as there are no jack points on the wing due to the large
deflections of the main gear springs. A sling should be constructed with each side of the sling attaching to a
chain or cable wrapped around the aft end of the engine mount at the firewall. Be sure to wrap rags around
the mount structure so as not to scratch the paint, and have the hopper empty before lifting. A two-ton hoist
should be used, and as the wheels clear the ground, place an empty 55 gallon drum with sufficient boards
under each wing at the tie-down location to steady the aircraft and provide safety in case the hoist should
fail. Do not attempt to jack the wings at the tie-down rings.
MAIN WHEELS
To remove a main wheel, jack the wheel clear of the ground per previous instructions. With a 7/16"
wrench, remove the six AN4 bolts attaching the two halves of each brake assembly. Leave the brake line
connected and slide the brake assembly out of the way. Next remove the snap ring on the inboard side of the
wheel that holds the felt grease retainer in place. This facilitates wheel removal and re-installation. Then
remove the outer snap ring and dust cap, remove the two cotters in the castellated nut, and back off the
castellated nut. The wheel can then be pulled free of the axle.
If the tire is to be removed, deflate and then remove the two wheel halves. When re-mounting the tire
and tube, apply enough air pressure in the tube to allow the tube to take shape and position itself properly in
the tire before the two rim halves are assembled. This will help prevent pinching the tube between the rim
halves. Torque wheel bolts 150 inch-pounds at the nut. Inflate to 50 psi. Clean bearings and hand-pack with
wheel bearing grease meeting Mil-PRF-81322 (such as Mobil grease 28) or Mobil SCH 100 grease. Before
the wheel is re-installed, inspect the cast aluminum torque plate for cracks and check the four axle attach
bolts for proper torque (800inch-pounds at the nut). Wipe axle clean and slide inner grease seal and bearing
on axle. Position wheel and tighten castellated axle nut until a slight bearing drag is felt when wheel is
turned. Back off nut to nearest castellation and install two MS24665-351 cotters. Position inner grease seal
and install snap ring. Install outer dust cap and snap ring and rotate wheel to check for possible drag of
cotter head on dust cap. The cotter head should protrude no more than 1/8" above the flat for dust cap
clearance. Check brake linings for wear and re-install on torque plate. The six AN4 bolts in each wheel
cylinder require 80-90 inch-pounds torque.
Main Wheel Alignment
1. Difference in forming of the main gear legs requires the use of tapered shims to provide the correct
camber and toe-in on the main wheels.
2. The aircraft is to be fueled, but with empty hopper. Taxi the aircraft a short distance in a straight line
to allow the gear legs to assume the natural position. The aircraft should be on paved surface or flat
smooth ground.
3. A long straight edge is placed across the front of the tires approximately at axle height. This straight
edge is supported by blocks, or cans, or both. A 24" or larger carpenters square is placed against the
straight edge and the outside surface of the tire, and held level with the ground at the axle height.
The tire should be square with the straight edge, or have up to 1/16" toe-in, measured at the most
outboard part of the tire.