AIR TRACTOR AT-502A User manual

AIR TRACTOR, INC.
Olney, Texas
AT-502A/502B/504
TABLE OF CONTENTS
DESCRIPTION SECTION
Page No.
GENERAL.............................................................................................................................. 1
CERTIFICATION BASIS........................................................................................................ 1
INSTRUCTIONS FOR CONTINUED AIRWORTHINESS (ICA’s) ......................................... 2
FUSELAGE............................................................................................................................ 3
WINGS .................................................................................................................................. 3
AILERONS............................................................................................................................. 3
Bendable Aileron Trim Tabs ..................................................................................... 4
FLAPS .................................................................................................................................. 4
EMPENNAGE ........................................................................................................................ 4
LANDING GEAR AND BRAKES............................................................................................ 5
Landing Gear ............................................................................................................ 5
Brake System............................................................................................................ 5
Brake System Schematic.......................................................................................... 6
ENGINE ................................................................................................................................. 7
INDUCTION SYSTEM ........................................................................................................... 7
EXHAUST SYSTEM .............................................................................................................. 8
FUEL SYSTEM ..................................................................................................................... 8
Fuel System Schematic ............................................................................................ 9
To Install Ferry Fuel System................................................................................... 10
To Remove Ferry Fuel System............................................................................... 11

AIR TRACTOR, INC.
Olney, Texas
AT-502A/502B/504
TABLE OF CONTENTS (Continued)
DESCRIPTION SECTION
Page No.
ENGINE CONTROLS .......................................................................................................... 11
PROPELLER AND GOVERNOR......................................................................................... 12
ELECTRONIC STARTING AND CHARGING SYSTEM...................................................... 13
Description................................................................................................................... 13
Theory of Operation..................................................................................................... 13
ELECTRICAL SYSTEM....................................................................................................... 14
COCKPIT ............................................................................................................................. 15
CONTROL SYSTEM............................................................................................................ 16
ENGINE DRIVEN AIR CONDITIONER ............................................................................... 16
DISPERSAL SYSTEM......................................................................................................... 17
DIGITAL PAYLOAD HOPPER QUANTITY INDICATION SYSTEM.................................... 18
HOPPER RINSE SYSTEM.................................................................................................. 19
BLEED AIR COCKPIT HEAT SYSTEM............................................................................... 19

Air Tractor, Inc. Description Page 1
AT-502A/502B/504 March 14, 2018
GENERAL
The Air Tractor AT-502A/502B/504 is an all-metal Cantilever low-wing monoplane designed especially
for agricultural operations. It is powered by a Pratt & Whitney PT6A turboprop engine which is highly suited
to ag flying. The standard engine for the AT-502B is the PT6A-15AG which is rated at 680 SHP. The
alternate engine for the AT-502B is the PT6A-34AG which is rated at 750 SHP. The PT6A-34AG engine is
standard for the AT-504. Installation losses are very low and the full horsepower can usually be obtained at
sea level temperatures up to 71ofor the -15AG and up to 87ofor the -34AG engines. The AT-502A can be
equipped with any of the following engines: the PT6A-140AG rated at 867 SHP, the PT6A-60AG rated at
1050 SHP, the PT6A-65AG rated at 1100 SHP, or the PT6A-45R flat rated at 1100 SHP. The marketing
term for the AT-502A with the PT6A-140AG engine is the "502XP".
The propeller for the 502B/504 is a Hartzell three-blade 106 inch diameter constant speed prop with
reversing capabilities. The 502A with the PT6A-140AG engine is equipped with a Hartzell 4-Blade 108-inch
diameter constant speed propeller with reversing capabilities. All other 502A airplanes are equipped with a
Hartzell 5-blade 111-inch diameter constant speed propeller with reversing capabilities. The hopper is made
of fiberglass and has a 500 gallon (U.S.) capacity. The horizontal stabilizer is all metal and strut-braced for
added rigidity. The vertical fin is cantilever. The elevators and rudder are of all-metal construction and
sealed to prevent chemical entry. The fuselage features removable skin panels for ease of maintenance and
cleaning. High-lift flaps are incorporated and are interconnected with the ailerons to provide extremely short
take-off and landing distances.
The AT-502A and AT-502B aircraft are single cockpit aircraft with a single seat. The AT-504 is two-
place with side by side seating and has dual controls for training.
CERTIFICATION BASIS
The AT-502A/502B/504 is structurally certified to meet the requirements of FAR 23. The engine
installation along with the systems and equipment meet FAR 23 requirements except in cases where
inappropriate for agricultural operations. In these cases placards are installed on the instrument panel which
prohibit flying under those special conditions. The AT-502A/502B/504 is certificated by the manufacturer for
a gross weight of 8,000 pounds. However, under the provisions of Part 8 the operator may select his own
maximum operating weight, and field experience shows that higher operating weights be carried safely with
adequate margins of performance and structural strength. See aircraft Type Certificate Data Sheet (TCDS)
and Service Letter #304 for more information.
Certification basis is FAR 21.25 (a) (1) including certain paragraphs of FAR 23 applicable to turbine
engine installations.

Description Page 2 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
INSTRUCTIONS FOR CONTINUED AIRWORTHINESS (ICA’s)
Maintain the airplane in accordance with the following manuals and documents:
LIST OF MANUALS AND DOCUMENTS
“Owner’s Manual- Air Tractor Model AT-502 Agricultural Airplane”
Document #03-0110
Air Tractor Inc.
Municipal Airport
P.O. Box 485
Olney, Texas 76374 U.S.A.
“Propeller Owner’s Manual & Log Book”
Manual 139
Hartzell Propeller Inc.
One Propeller Place
Piqua, Ohio 45356-2634 U.S.A
“Maintenance Manual- Turboprop Gas Turbine Engine- Model PT6A-15AG”
Manual Part No. 3030442, Vols. 1 & 2
“Maintenance Manual-Turboprop Gas Turbine Engine-Models PT6A-34AG”
Manual Part No. 3021242, Vols. 1 & 2
“Maintenance Manual-Turboprop Gas Turbine Engine-Models PT6A-45R”
Manual Part No. 3027042, Vols. 1 & 2
“Maintenance Manual-Turboprop Gas Turbine Engine-Models PT6A-60AG”
Manual Part No. 3034342, Vols. 1 & 2
“Maintenance Manual-Turboprop Gas Turbine Engine-Models PT6A-65AG”
Manual Part No. 3032842, Vols. 1 & 2
“Maintenance Manual-Turboprop Gas Turbine Engine-Models PT6A-140AG”
Manual Part No. 3079582, Vols. 1 & 2
Pratt & Whitney Canada
1000 Marie-Victorin
Longeuil, Quebec
Canada J4G 1A1

Air Tractor, Inc. Description Page 3
AT-502A/502B/504 March 14, 2018
FUSELAGE
The fuselage structure is of heli-arc welded 4130N steel tubing. All fittings and bushings are also of
4130N steel. Fuselage repairs may be made in accordance with appropriate FAA repair procedures and gas
welding is permissible. There are no heat-treated members in the fuselage. The front section of the fuselage
from the rear spar forward and including the engine mount have been oven stress-relieved in order to
prevent stress concentrations from the welding operation. For corrosion control oil passage holes are drilled
at the intersections of all tubes and clusters. Hot linseed oil is then pumped into the fuselage frame and
drained. This oil adheres to the inside walls of the tubing. The exterior of the fuselage frame is then sand-
blasted and painted with AG Air Yellow Epoxy which is resistant to nearly all chemical action.
The fuselage lower and upper skins are attached to the fuselage frame with stainless screws and nuts.
The fuselage side panels are of heavy gauge 2024-T3 alclad or 6061-T6 and are attached to stainless
camloc receptacles. This allows the side panels to be removed in minutes, leaving the fuselage frame open
for thorough cleaning and inspection. All skins are mounted with clearance between the skin and the
fuselage tubing so that chemicals will not collect and cause corrosion.
WINGS
The wing structure is full cantilever, with the main spar carrying all of the bending loads. Construction
is of 2024-T3 alclad for skins and spar webs. The upper spar cap is also 2024-T3 material, but the lower spar
cap is made of alloy steel for a long fatigue life. The wing has a constant chord of 72 inches and a span of
52.0 ft. The wing utilizes a NACA 4415 wing section and has 2 degrees of washout twist.
The leading edge is extra heavy with a leading edge doubler bonded internally to minimize denting.
Each wing panel has the leading edge divided into five different pieces to allow easy replacement. Universal
head rivets are used to facilitate the removal and replacement of leading edge sections.
The fuel tanks are located in the inboard section of the wing and are an integral part of the structure.
The closely riveted seams and heavy skins make them burst resistant in the event of a crash. Sealing is
accomplished by an application of Courtalds Aerospace PR-1442 Class A and Class B sealing compound*.
The inboard end of the wing is sealed against chemical entry and the aileron pushrod has a flexible boot
attached to prevent entry of chemical at the pushrod location. A complete wire bundle for night working lights
is installed inside the wing during assembly so that lights may be added at a later date.
The upper spar cap is painted with yellow polyurethane paint and the lower spar is cadmium plated
and primed for corrosion protection. All other parts inside the wing are treated with alodine and primed prior
to assembly.
* Alternate sealers are Morton Aerospace MC-236 Class A and Class B, AC-Tech AC-236 Class A and
Class B, PRC DeSoto International P/S 890 Class A and Class B, and AC-Tech AC250 Class A and Class B.
AILERONS
The ailerons are of all-metal construction and hinged on ball bearings. The bellcranks and pushrod
ends operate on ball bearings, producing smooth operation and low system friction. The stick forces are light
and the ailerons are very responsive. The light stick forces are a result of the installation of aerodynamic
servo tabs installed on the outboard end of each aileron.
The ailerons are interconnected with the wing flaps so that as the flaps move down through 26o, the
ailerons droop 10o. The interconnection is non-linear so that most of the aileron droop occurs with the first
half of the flap travel. This provides optimum conditions for short take-off performance.

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March 14, 2018 AT-502A/502B/504
Each aileron has a large balance weight on the outboard end of the aileron just forward of the leading
edge. These weights must never be removed as they are necessary for flutter prevention.
Bendable Aileron Trim Tabs
Small bendable aileron trim tabs are installed on the trailing edge of each aileron. These tabs allow
the pilot to make minor adjustments to the airplane’s roll trim by adding a small amount of up or down force
to the trailing edge of the aileron in flight.
To make an aileron trim adjustment, fly the airplane at normal cruise power and normal cruise speed
in smooth air. While flying the airplane in coordinated flight (ball centered), evaluate the airplane’s natural
rolling tendency with the controls free, and evaluate the amount of stick force required to fly the airplane
wings level. In the case of “left wing heavy”, the pilot should bend the left bendable tab trailing edge UP, and
the right tab trailing edge DOWN. Use a hand seamer or other similar tool to make a clean, even bend.
Avoid excessive bend angle, because the bendable tabs will stall and become ineffective at bend angles
greater than 20 degrees. Make tab adjustments in small increments, and re-fly the airplane to re-evaluate
roll trim.
FLAPS
Extra large Fowler-type flaps are incorporated on the Air Tractor. The flaps are electrically operated
and may be stopped at any position from 0oto the maximum of 26otravel. The flaps are controlled by a switch
conveniently mounted just below the throttle quadrant. The flaps have external markings which may be
viewed from the cockpit with each of the first two marks being 10oof travel.
The flaps are very effective for both take-off and landing. For a short take-off roll, 10oof flap is normally
used. The flaps are also useful during turns, although no more than 10oshould be used.
EMPENNAGE
The horizontal stabilizers are all-metal and strut-supported for rigidity. The struts are constructed of
streamlined 4130N tubing. The struts have a stainless clevis where the attachment to the stabilizer is made
and the clevis is adjustable in order to rig the stabilizers properly with the wing and in a straight line from side
to side.
The vertical fin is cantilever and is of all-metal construction. It has a relatively short span in order to
minimize the hazards of working under telephone lines or other obstructions. A heavy-duty wire deflector
cable is attached to the top of the vertical fin and extends to the top of the canopy where it is anchored.
The control surface hinges have a single stainless steel ball with a Teflon lining. Long bearing life can
be expected and it is not necessary to lubricate the hinge.
The elevator trim tabs act as Servo tabs in addition to providing longitudinal trim for the Air Tractor.
Because of the large tab size, the trim tabs provide a considerable amount of trim authority. Removable
bronze bushings are provided at each joint. As the bushing wear, they should be replaced so that trim tab
free play may be kept to a minimum. The all-metal rudder has a servo tab that also serves as an adjustable
trim tab.

Air Tractor, Inc. Description Page 5
AT-502A/502B/504 March 14, 2018
LANDING GEAR AND BRAKES
Landing Gear
A spring type main and tail landing gear is used on the Air Tractor. This type of landing gear provides a
minimum of maintenance, low drag and considerable energy absorption for hard landings. In addition, a
smooth ride is provided for operations from rough strips.
The main gear axles are made of alloy steel, and cadmium plated for corrosion protection. Tapered
aluminum shims are used between the axle and the main gear leg to provide the proper camber and toe-in.
The main gear wheels are Cleveland p/n 40-133 with a 29x11.00 10-ply rating tire installed. Main wheel tire
inflation pressure is 50 psi (unloaded) or 52 psi (loaded).
The tail wheel is a Cleveland 40-168. A grease fitting is provided in the side of the wheel in order to
grease the bearings.
The tail wheel tire is 5.00x5. Be sure it is 6-ply rating. Tire pressure is 50 psi loaded or unloaded.
The tail wheel fork is of welded 4130N tubing construction and is heat-treated for strength. Bronze
bushings and a brass wear plate are incorporated where the fork enters the tail wheel housing. A tail wheel
locking mechanism is provided and the tailwheel may be unlocked by pushing the control stick forward. This
lifts the stainless locking pin out of the tail wheel fork and allows the tail wheel assembly to swivel 360o. If
during taxi the aircraft tends to steer to the left or to the right with the controls neutral, it is possible to
readjust the lock pin position by loosening the 4 screws that attach the lock pin housing to the fork housing
plate. The lock pin can then be moved in the desired direction and the screws tightened.
Brake System
Brakes are the same, left or right, and are Cleveland p/n 30-98C. The brake cylinders are Cleveland
p/n 10-23F. Brake fluid is the conventional red petroleum-base Mil-H-5606A fluid. The brake fluid reservoir is
a Volkswagen p/n 113611301 L and is mounted on top of the lower instrument panel where the fluid level is
always visible. The parking brake valve is a Scott p/n 4500A-2. Stratoflex hoses are used from the pressure
side of the master cylinder to the parking brake valve and stainless steel lines are routed from the valve to
the bulkhead fitting next to the main landing gear. A high-pressure Stratoflex hose connects the bulkhead
fitting to the wheel cylinders.

Description Page 6 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504

Air Tractor, Inc. Description Page 7
AT-502A/502B/504 March 14, 2018
ENGINE
The usual engine choice for the AT-502B/504 is a Pratt & Whitney PT6A-34AG turboprop engine. This
engine is rated at 750 HP for take-off at sea level and 87oF. Maximum torque at take-off is 1790 ft-lbs.
Maximum ITT for take-off is 725oC. Maximum Ng is 101.5% for take-off. Maximum Np for all operations is
2200 RPM.
The AT-502B can also be equipped with a Pratt & Whitney PT6A-15AG turboprop engine. This engine
is rated at 680 SHP and 1628 ft-lbs of torque for takeoff. Maximum ITT for takeoff is 725 °C. Maximum Ng
is 101.5% and maximum Np for all operations is 2200 RPM.
The standard engine for the AT-502A is the PT6A-60AG. This engine is rated at 1050 SHP. Maximum
torque for take-off is 3245 ft-lbs. ITT maximum is 820oC. For airplanes with the PT6A-65AG, the engine is
rated at 1100 SHP and 3398 ft-lbs of torque on takeoff with a maximum ITT of 820 °C. For airplanes with the
PT6A-45R, the engine is rated at 1100 SHP and 3398 ft-lbs of torque on takeoff with a maximum ITT of
800 °C. The maximum Ng for these engines is 104.0% and the maximum Np for all operations is 1700 RPM.
AT-502A aircraft with the PT6A-140AG engine have a maximum of 867 SHP and 2397 ft-lbs on takeoff
with a maximum ITT of 870 °C. The maximum Ng is 103.7% and the maximum Np for all operations is
1900 RPM.
For long engine life it is recommended that the I.T.T. is kept well below the maximum limits. Use only
enough power on take-off to operate safely from the strip being used.
See the flight manual for other engine limits and special conditions. Read the engine maintenance
manual for instructions as to care and servicing of your engine.
INDUCTION SYSTEM
Engine air is drawn in through the inlet scoop, through a barrier type filter and into a sealed plenum
which is located between the forward and aft engine firewalls. There are three different filter installations that
Air Tractor has used on AT-502A/502B/504 aircraft. Each of these filter installations is over 99% efficient
and cause only a negligible pressure drop due to the ram air pressure developed by the air scoop.
The earliest air filter system used two large, cylindrical commercial truck filters. These filters are Donaldson
p/n P182043 (alternate is P510337) for the AT-502B/504 and Donaldson p/n P181008 (alternate is P510335)
for the AT-502A. Aircraft equipped with the Air Tractor Ram Air system have the airscoop moved from the
lower side of the engine cowling to the nose of the aircraft, just below the propeller. This Ram Air
configuration may have one of two different filter systems. The first system uses a pleated filter element
made by Donaldson (p/n P613731 for the AT-502B/504, p/n 52427-17 for the AT-502A (w/ -45R, -60AG, and
-65AG engines)) pleated filter element. This filter looks like a paper element filter, but is actually synthetic.
The second type of Ram Air filter is a Brackett foam air filter. This filter is a disposable foam Description
element filter that contains a sticky residue “wettant” that traps and holds dirt and debris. This is a
lightweight, flexible filter that is installed in a stainless steel frame inside the engine plenum. The part
number for the Brackett foam filter is BA-409E for the AT-502B/504 and BA-413E for the AT-502A (w/ -45R,
-60AG, and -65AG engines).
A pressure differential switch is installed on the top R/H side of the aft firewall with one probe in the
engine area and the other probe in the plenum. At such time that the pressure difference between the air in
the engine area and the air in the plenum reaches the set point, the air filter light on the instrument panel will
come on. The set point is 13 inches of water vacuum for AT-502B/504 aircraft and AT-502A aircraft with the
PT6A-140AG engine. The set point is 15 inches of water vacuum for AT-502A aircraft with the
PT6A-45R/-60AG,-65AG engines. This light has a “push to test” feature and should be checked before the
engine is started.

Description Page 8 Air Tractor, Inc.
March 14, 2018 AT-502A/502B/504
EXHAUST SYSTEM
The 502B/504 exhaust pipes are Air Tractor p/n 50597-3 (L/H) and p/n 50670-1 (R/H). These pipes are
attached with stainless MS20034-1 bolts, MS20500-428 nuts, and AN960C416 washers. There are exhaust
covers provided with each aircraft and these covers should be installed when the engine has cooled. The
AT-502A uses p/n 51238-7 (L/H) and p/n 51238-6 (R/H) exhaust pipes when the PT6A-45R, -60AG, or
-65AG engines are installed. AT-502A aircraft with the PT6A-140AG engine use Air Tractor p/n 50597-3
(L/H) and p/n 50670-1 (R/H) exhaust pipes.
FUEL SYSTEM
Standard 502B/504 aircraft have two fuel tanks with a capacity of 85 U.S. gallons each. Both tanks
gravity feed into a small header tank which is located behind the chemical hopper and below the rear spar
attach tube. Optional fuel capacity is either 216 or 234 gallons for the 502B/504. The 502A standard fuel
capacity is 216 gallons.
The fuel valve handle is located within easy reach of the pilot and is marked “Main” and “Off”. There
can be no tank selection since both tanks are interconnected. The fuel valve is placarded in “Gallons
Usable”. The fuel gauge receiver, which is located on the instrument panel, is marked in fractions of usable
fuel. Finger strainers of coarse wire mesh are located in each fuel tank. Fuel flows from the wing tanks into
the header tank, through the fuel valve and to the airplane firewall. From the firewall, a fuel line is connected
to a large fuel filter. This fuel filter may be either a Fram FS1133-PLM or Air Tractor p/n 53114-1 fuel filter
(AT-502A model aircraft use a 53114-2 fuel filter). All fuel filters use an Air Tractor p/n 52351-1 fuel filter
element. The p/n 52351-1 fuel filter element should be cleaned at 100-hour intervals or as required,
depending on how clean the fuel is that is being used. A vacuum pressure switch is connected to the outlet
side of the filter. If the filter becomes clogged, the switch will close and the “FUEL FILTER” warning light will
illuminate in the cockpit.