AIR TRACTOR AT-502A, Maintenance Section

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Maintenance Page 66 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
Secure the wings to the ground anchors using the wing tie-down rings located beneath the front
spars of each wing, and secure to the ground anchors. These lines should be oriented as close to vertical as
possible (within 30 degrees of vertical). The tail wheel is secured by wrapping and tying the tie-down line
around the tailwheel spring. This line should be tied to a ground anchor located slightly aft of the tail wheel.
Use care to avoid damaging the tail wheel lock mechanism.
If winds in excess of 20 mph from the rear of the aircraft are expected or possible, suitable blocks
should be used to lock the control surfaces (ailerons, elevators, and rudder) in place and relieve strain on the
control systems. Very large damaging dynamic loads are possible with a gusty reverse flow of air over the
control surfaces. Should this happen without blocks in place, be sure to check all push-rods and rod-ends in
the aileron control system for damage before flight.
TOWING INSTRUCTIONS AND LIMITATIONS
The airplane can be towed with the use of an appropriate tow bar attached to the main landing gear.
The proper towing points are the sheet metal rings on the inner side of the landing gear strut in the same
plane as the axle. Towing with attachment to the tail-wheel spring is not recommended. The tail-wheel lock
should always be disengaged while the airplane is being towed.
A towing bar can be made from two 12-foot-long 4130 steel tubes and a three-quarter-inch steel bar.
The tube's outside diameter should not be less than two inches and the wall thickness should be at or above
.065 inch.
The tubes are pinned together at one end with a loose 1/2-inch bolt and an attachment to join to the
towing lug or ball on a vehicle. The three-quarter-inch steel bar is bent at 90 degrees with four inches of bar
extending in one direction and three inches in the other direction from the bend. These bent bars are welded
to the free ends of the tubes. The three-inch leg is pointed downward and the other is fillet-welded to the
bottom of the tube. These downward-projecting pintles fit loosely into the towing rings in the airplane's
landing gear. A hole may be drilled through the three-inch leg at a quarter-inch from its end for a spring pin, if
desired.
The airplane can be pulled or pushed using the tow bar. If the airplane is towed into tight quarters, a
wing-walker should be engaged to avoid damage to wing tips and tail members where visibility is limited.
The airplane should not be towed faster than 5 miles per hour on a smooth surface without chug-
holes or sharp bumps. Landing gear damage, particularly tail-wheel damage, can result from dropping the
gear into holes at high speeds. Excessively bumpy surfaces must be negotiated cautiously to avoid landing
gear damage. Also, bumpy surfaces may cause the tow bar to bounce and disengage from the tow rings on
the landing gear. Should this occur, directional control of the airplane is lost. A gentle stop should be
executed immediately to minimize damage. The safest approach to towing on bumpy surfaces is to station a
crew member in the pilot's seat to actuate the airplane's brakes if the hitch or tow bar should fail or
disengage. Use of a spring pin through the drilled holes minimizes the likelihood that the tow pintles will
bounce free.
Sloped surfaces with a grade more than ten degrees should be approached diagonally to reduce the
load on the tow bar and hitch points.
Sudden starts and stops must be avoided, particularly with a heavily-laden airplane, to prevent
failure of the tow bar or tearout of the towing rings.