AIR TRACTOR AT-502A, Maintenance Section

Page: 41 / 159

Maintenance Page 22 Air Tractor, Inc
March 14, 2018 AT-502A/502B/504
Check the torque on the two NAS1306-13 bolts at 300 hour intervals. If the bolt is held stationary and the
torque wrench applied to the nut, the torque value should be 420 inch-pounds. For the reverse of this
procedure, torque should be 460 inch-pounds.
The rear spar attaches to the fuselage frame with AN3 bolts of various lengths, depending on the
amount of shims required between the fuselage frame and the rear spar. The shims are of various thickness
(.063, .080, .125) and the upper shims are combinations of p/n 30159-1, -2, or -3 while the lower shims are
combinations of p/n 30160-1, -2, or -3.
The vertical fin rear spar is drilled on installation where the attachment is made to top longeron. If a
new fin is installed, make a drill template from the original fin rear spar in order to drill the four 3/16" holes for
the attachment to the upper longeron. The template should be 2.44" wide and long enough to pick up the two
lower attach bolts. The template should be made of either aluminum or steel, at least .063" thick.
Install the fin on the aircraft and install the bolts at the front and rear spar locations. Be sure the correct
amount of shims is used between the fuselage frame and the rear spar. The NAS1306-13 front spar bolts
have a torque of 420 inch-pounds at the nut. The rear spar bolts have a torque of 60 inch-pounds at the nut.
RUDDER
The rudder is attached to the vertical fin with three AN4-10A bolts, with a AN960-416 washer under the
bolt head, and two washers under the AN365-428A nut. The rudder hinges have NMB p/n ABT4 bearings
installed, which are staked on each side of the 1/4" thick hinge fitting. Since there is a certain amount of drag
with these spherical bearings, it is very important to fully torque (100 inch-pounds at the nut) the three AN4-
10A bolts that attach the rudder to the fin. If the bolts are loose, the bolts will turn on the fin hinge brackets
and cause the holes to become elongated.
The bearings have little wear, but if it is necessary to replace them, construct a “puller” that will apply
force to the outer ring of the bearing with the opposing force against the aluminum housing. A AN4 bolt
through both parts of the “puller” should be tightened until the bearing rim is pulled past the stake marks and
the bearing comes out of the housing. When the new bearing is installed, re-stake with a center punch.
The rudder horn is p/n 70092-1 and has two p/n 70093-1 bushings installed for wear at the cable
attachment. The horn is attached to the rudder assembly with two AN4C7A bolts.
Rudder control stops are at the rudder horn and the rudder travel is 21
o
Left, 21
o
Right, +/-1
o
.
RUDDER CONTROLS
AT-502A/502B
The rudder cables are p/n 70095-6 and attach to stainless link plates (p/n 70094-1) at the rudder horn
with AN4C10 bolts, AN310C4 nuts, AN960C416 washers, MS24665-151 cotters. There are four MS24566-
3B pulleys in the rudder cable system to the cockpit.
In the cockpit, the rudder cables attach to a steel p/n 70096-1 plate which is bolted to a p/n 70101-1
aluminum adjust channel. Also attached to the 70096-1 plate is a p/n 70098-1 cable assembly which
interconnects the rudder with the aileron control system. The interconnect springs under the cockpit floor are
p/n 70103-1 and attach to a MS21255-3LS cable eye, MS21251B3S barrel, MS21255-3RS cable eye,
AN100C4 thimble and 18-2-G Nicopress sleeve.
The rudder pedal hanger assembly (p/n 70109-1) slides in the adjust channel and is held in place with
a D5-10T-303 Faspin. The hanger assembly has a spring attached to pull it forward to remove slack from the
rudder cable. The spring is attached to an eyebolt in the hanger assembly and is p/n 70102-1.