AIR TRACTOR AT-502A, Секция обслуживания, Страница: 36 / 159

Air Tractor, Inc. Maintenance Page 17
AT-502A/502B/504 March 14, 2018
The support frame (p/n 70072-1) is attached to the floor structure with a AN4-50A bolt. There are two
Fafnir KP6A bearings in the support frame and a 70081-1 stainless bushing allows full bolt torque same as
with the 70076-1 bellcrank. The KP6A bearings are sealed and require no lubrication. Some end play will
develop due to tolerance accumulation, but up to .040" is acceptable.
The aileron bellcranks in the wings are attached to a welded structure with an AN4-46A bolt and have
a p/n 70081-3 stainless spacer to allow full bolt torque. Bearings are Fafnir KP6A. The wing bellcranks are
p/n 70079-1 (L/H) and 70079-2 (R/H). Maximum end play of the wing bellcrank is .03". The bolt attaching the
wing bellcranks may be reached by removing the plug buttons (11/16) on the top and bottom skins. To
remove the bellcrank from the wing it is necessary to remove some rivets attaching the lower wing skin.
Remove rivets that can be easily reached for re-installation.
The 90
o
bellcranks that connect to the flap torque tube are p/n 70082-1 and are interchangeable R/H to
L/H. They are connected to the fuselage frame with AN 6-34A bolts and a p/n 70085-1 spacer bushing to
allow full torque of 300 inch-pounds to be used during bolt installation. At each end of the spacer bushing is a
90011-1 large washer to contain the Torrington p/n B812 needle bearing. These needle bearings should be
checked, cleaned, and packed with general purpose grease once a year during annual inspections. During
re-assembly, make sure that the 70085-1 spacer bushing has been faced off square on each end because if
it is not, the slight chamfer or bevel will cause the 90011-1 washer to distort and drag the bellcrank face. With
the AN6-34A bolt fully torqued, there should be positive clearance between the 90011-1 washers and the
bellcrank, with end play not to exceed .03". Check the bellcrank end for excessive wobble, which would
indicate a worn needle bearing, spacer bushing, or both. The needle bearing should hand press-fit into the
bore of the bellcrank, and the spacer bushing should be a loose sliding fit inside the needle bearing. The bolt
should make a loose sliding fit on the spacer bushing. While the bellcrank is removed, check for any sign of
bending of the plates or cracks in welds. These bellcranks are subject to bending if the aircraft is parked with
the tail into a high wind and the ailerons begin a flutter motion even though the stick is locked. If the
bellcranks are bent, replace them.
The flap torque tube is attached to the fuselage frame with two AN4-10A bolts. The bearings which are
pressed into the torque tube fittings and staked are NMB p/n ABT4 and are spherical bearings with a
stainless ball and a teflon lining. As this type of bearing has some drag, be sure the AN4-10A attach bolts are
fully torqued. These bearings do not require lubrication. The 2.0" diameter flap torque tube consists of the
welded assembly and bearings only. At the extreme end of each side of the torque tube is a 1/4" aluminum
arm (p/n 70027-1) which also has a NMB p/n ABT4 bearing installed. The two flap push-rods attach to the
bearings with AN4-10A bolts and should be torqued to 100 inch-pounds at the nut same as the fuselage
attach bolts.
Two smaller 1/4" alumi
num arms attach the torque tube to the flap actuator “Tee”. These arms are p/n
70032-1 and have a KP6A bearing pressed into place and staked.
FLAP ACTUATOR
The flap actuator assembly is a Commercial Aircraft Products p/n D-145-00-35. This actuator uses
micro-switches to limit the down and up travel of the flaps. The micro-switches are p/n BZ2R5551-A2 and the
arm with the roller attached that actuates the micro-switch is an AN3169-1 arm. The motor for the actuator
can be purchased separately and is p/n C-145-355. The actuator assembly attaches to the fuselage frame
with a AN4-16A bolt. At this connection there is also a 70026-1 spacer bushing and a Bunting P31-8 bronze
bushing. If the actuator is replaced or removed, be sure both bushings are in place.