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AIR TRACTOR AT-502A Maintenance Section

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ENGINE MAINTENANCE ................................................................................................................. 01
Introduction .......................................................................................................................... 01
Maintenance ......................................................................................................................... 01
Cleaning Your Engine Exterior ............................................................................................. 01
................................................................................................................................ 02
Figure 101 Fuel Nozzles ...................................................................................................... 03
................................................................................................................................ 03
Figure 102 Location of Oil Drain Plugs ................................................................................ 04
Air Filters .............................................................................................................................. 05
Miscellaneous ...................................................................................................................... 06
Compressor Washes............................................................................................................ 07
Figure 103 Gas Generator Case .......................................................................................... 07
Troubleshooting ................................................................................................................... 08
Starting Procedures ............................................................................................................. 08
Ground Run Procedures ...................................................................................................... 09
Routine Maintenance Inspection ........................................................................................ 010
INTRODUCTION ................................................................................................................................. 1
FUEL REQUIREMENTS ..................................................................................................................... 1
OIL REQUIREMENTS ........................................................................................................................ 1
AIR TRACTOR, INC.
Olney, Texas
AT-502A/502B/504

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MAINTENANCE SECTION
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Summary of Contents for AIR TRACTOR AT-502A

  • Page 1: Table Of Contents

    AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS MAINTENANCE SECTION Page No. ENGINE MAINTENANCE ......................... 01 Introduction .......................... 01 Maintenance ......................... 01 Cleaning Your Engine Exterior ..................... 01 Fuel ..........................02 Figure 101 Fuel Nozzles ...................... 03 ..........................03 Figure 102 Location of Oil Drain Plugs ................
  • Page 2 AIR TRACTOR, INC. Olney, Texas AT502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. TIRE INFLATION ..........................1 LIFTING AND JACKING ........................1 MAIN WHEELS ........................... 2 Main Wheel Alignment ......................2 BRAKES .............................. 3 Brake Master Cylinders ......................3 Brake Bleeding ........................
  • Page 3 AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. FUEL TANKS ............................ 12 Fuel Tank Senders ....................... 13 Fuel Tank Receiver ......................13 FUEL SYSTEM DRAINS ........................14 FUEL SYSTEM SCREENS AND FILTERS ..................14 AILERONS ............................
  • Page 4 AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. ELEVATOR CONTROL ........................24 COCKPIT CONTROLS ........................25 ELEVATOR TRIM TABS ........................26 TRIM TAB CONTROLS ........................26 TRIM LEVER ............................. 27 FUSELAGE REMOVABLE SKINS ....................27 FUSELAGE FIXED SKINS........................
  • Page 5 AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. Service Procedures ......................41 Common Causes of Compressor Failure ................46 HOPPER ............................47 HOPPER GATE BOX ........................47 HOPPER LID ............................ 48 GATE BOX CONTROLS ........................48 SPRAY LEVER CONTROLS ......................
  • Page 6 AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. Voltage Regulator ........................ 54 Charging System Troubleshooting Guide ................55 Troubleshooting Procedures ....................56 Lighting System Troubleshooting ..................58 Checking the Batteries ......................59 Oil Cooler Blower ......................... 60 Engine Instruments ......................
  • Page 7 AIR TRACTOR, INC. Olney, Texas AT-502A/502B/504 TABLE OF CONTENTS (Continued) MAINTENANCE SECTION Page No. AVIONICS ............................63 LIFE LIMITED ITEMS ........................63 PROPELLER MAINTENANCE ......................64 TIE-DOWN INSTRUCTIONS ......................65 TOWING INSTRUCTIONS AND LIMITATIONS ................66 DRAINING THE STATIC SYSTEM ....................67 LOW FUEL WARNING SYSTEM .....................

  • Page 8: Engine Maintenance

    Air Tractor, Inc. Maintenance Page 01 AT-502A/502B/504 March 14, 2018 ENGINE MAINTENANCE Introduction This section of the Maintenance/Inspection manual written by Van B. Dardis, Lubbock, Texas. The Pratt & Whitney PT6A series of engines have been proven to be one of the most reliable powerplants available today.

  • Page 9: Fuel

    Air Tractor recommends the use of Jet A fuel that has been treated with a Fuel System Icing Inhibitor (FSII) such as Prist. Some Jet A comes from the supplier with FSII in it and some does not, so check with your supplier to be sure.

  • Page 10: Oil

    Air Tractor, Inc. Maintenance Page 03 AT-502A/502B/504 March 14, 2018 The earlier model of PT6A engines came with 7 primary and 7 secondary nozzles. The engine starts on the primary nozzles and at about 35% Ng the secondary nozzles come in. The engineers at Pratt & Whitney have discovered that the engine will start cooler by reducing the number of secondary nozzles, hence Service Bulletin 1372.
  • Page 11 Maintenance Page 04 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 LOCATION OF OIL DRAIN PLUGS 2. CHIP DETECTOR 7.OIL TANK DRAIN 10. ACCESSORY CASE DRAIN Figure 102...

  • Page 12: Air Filters

    The PT6A engine requires a large amount of air at full power settings. To handle this load while adequately cleaning the air, your Air Tractor is equipped with large, efficient air filters. The length of service for these filters depends entirely on the operating conditions. When you replace these filters, use the original equipment filters for replacement.

  • Page 13: Miscellaneous

    March 14, 2018 AT-502A/502B/504 For AT-502A (all engines except the PT6A-140AG) aircraft with the p/n 52427-17 Ram Air filter, removal of the filter is accomplished by removing the lower and side cowl skins from the aircraft. Then completely remove the lower plenum cover to gain access to the filter. From the righthand side of the airplane, remove the filter retaining band on the aft plenum bulkhead by removing the eight bolts that hold it in place.

  • Page 14: Compressor Washes

    Compressor washes are performed to remove dirt and deposits which hamper the efficiency of the compressor. The quality of the Air Tractor induction system is so good that most engines require a compressor wash only once a year. An inspection of your engine inlet is a good indicator of when to perform a compressor wash.

  • Page 15: Troubleshooting

    24 volts, put them in a cart for ease of movement, and connect them to cables with a plug compatible to your Air Tractor. It is also convenient to wire a trickle charger to a female socket like your airplane has and you can keep the batteries plugged in when not in use so they will always be ready when needed.

  • Page 16: Ground Run Procedures

    March 14, 2018 Ground Run Procedures The following are Air Tractor’s recommendations on performing ground engine runs. These recommendations apply to all Air Tractor aircraft: 1. It is recommended that the hopper be filled with water prior to performing ground runs.

  • Page 17: Routine Maintenance Inspection

    Maintenance Page 010 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Routine Maintenance Inspection The following is a guide to your routine maintenance inspections. It is not an absolute, but intended to be a guide to help you in establishing a schedule that will maintain your engine in the proper manner. For complete maintenance inspection schedule see the appropriate Pratt &...
  • Page 18 Air Tractor, Inc. Maintenance Page 011 AT-502A/502B/504 March 14, 2018 Miscellaneous __________ VERIFY ACCURACY OF ITT GAUGE EVERY TWO YEARS __________ OVERHAUL STARTER-GENERATOR AT 1000 HOURS __________ DYNAMIC BALANCE PROPELLER AT 1000 HOURS __________ REPLACE AN47-22A EYEBOLTS ON HOROZONTAL STABLIZER (REFERENCE SL 129) TORQUE TO 600 IN-LBS AT 1350 HOURS.
  • Page 19 This Page Intentionally Left Blank...

  • Page 20: Fuel Requirements

    Air Tractor, Inc. Maintenance Page 1 AT-502A/502B/504 March 14, 2018 INTRODUCTION This section is presented to describe maintenance functions that are applicable to the AT-502/504 airplane. Airframe maintenance items that are not specifically covered in this section are addressed in FAA Advisory Circular (AC) 43.13.

  • Page 21: Main Wheels

    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.

  • Page 22: Brakes

    Air Tractor, Inc. Maintenance Page 3 AT-502A/502B/504 March 14, 2018 Camber is then measured by placing a protractor on the vertical axis of the wheel through the axle. Camber should measure 1 to 2 Should the wheel fail to check within these limits, the axle bolts are removed and the tapered shims rotated, deleted, or added to until the wheels check with these limits.

  • Page 23: Brake Bleeding

    Maintenance Page 4 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 If a spot of brake fluid appears on the cockpit floor on the L/H side it does not necessarily mean that the master cylinder is leaking. The usual cause is over-filling the brake reservoir, so that when brakes are used, and fluid returns to the reservoir, it sometimes leaks through the vent hole in the reservoir cap.

  • Page 24: Tail Wheel Fork

    Air Tractor, Inc. Maintenance Page 5 AT-502A/502B/504 March 14, 2018 the jam nut from the axle and remove the axle. Inspect the axle for wear at the bearing positions, as insufficient greasing procedures will cause the bearing to turn on the axle and ruin both parts. Inspect the AN6 bolt for wear and straightness, and slide the bolt through the fork to check the hole in the fork for wear.

  • Page 25: Tail Wheel Lock Pin And Housing

    Some strips are so rough you wouldn’t dare drive your empty pickup over 30 mph down the strip, yet there goes an Air Tractor with a ton of fertilizer bouncing along at 80 mph on a still day just before lift-off.

  • Page 26: Tail Gear Spring

    Air Tractor, Inc. Maintenance Page 7 AT-502A/502B/504 March 14, 2018 you are the one with the potholes or super-rough strips, cut the time between bolt changes in half. If your aircraft hits the ground or a ditch bank during spraying, change the forward clamp bolts immediately. If you discover slack in the large 1.0"...

  • Page 27: Main Gear Spring

    At various intervals this measurement should be checked, and after 1,000 hours check the measurement at least every 50 hours. Although service history for the Air Tractor is relatively limited, it appears that the tail spring should be changed about every 1500 hours for worst conditions of rice operations from rough strips, and every 2,000 hours for the best conditions of row-crop work from smooth strips.
  • Page 28 Air Tractor, Inc. Maintenance Page 9 AT-502A/502B/504 March 14, 2018 The method employed at the factory to determine the amount of shims required is to install the clamp block and fully torque the bolts before installing the large inboard bolt. The block is checked for straightness with a small straight edge (a six-inch steel scale is OK) to be sure the block is not bent by not having sufficient shims.

  • Page 29: Wings

    Maintenance Page 10 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 WINGS The wing is of all-metal construction with the main spar designed to take all of the bending load. Thick wing skins are employed near the wing root with a gradual drop in thickness at each skin lap as wing loads diminish.

  • Page 30: Wing Center Splice Connection

    Air Tractor, Inc. Maintenance Page 11 AT-502A/502B/504 March 14, 2018 Wing Center Splice Connection The main spar caps of each wing are attached to each other with p/n 20591-1/-2 attach blocks (Upper) and p/n 21076-1/-2 attach blocks (lower) which are line reamed and cold worked with the spar cap as a matched set.

  • Page 31: Fuel Tanks

    Maintenance Page 12 Air Tractor, Inc. March 14 2018 AT-502A/502B/504 FUEL TANKS The fuel tanks are sealed with PR-1422-A2 which is brushed on and PR-1422-B2 which is a thicker putty-like material for sealing corners or large cracks. Sealing between mating parts is done during assembly, and final coating is done through the five inspection openings in the top of the tank.

  • Page 32: Fuel Tank Senders

    Air Tractor, Inc. Maintenance Page 13 AT-502A/502B/504 March 14, 2018 Fuel Tank Senders The L/H fuel tank sender has a shorter float arm than the R/H sender and is positioned differently in the tank. For these reasons the cork at the end of the float arm is still about 3" from the bottom of the fuel tank when the L/H sender is at the end of its stroke and the receiver on the instrument panel shows “E”.

  • Page 33: Fuel System Drains

    Maintenance Page 14 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Remove the L/H fuel line from the tank and cap the L/H tank outlet. Plug the line to isolate the two tanks. Turn on the battery switch and set the needle on “E” with the adjust screw on the face of the receiver.

  • Page 34: Flaps

    Air Tractor, Inc. Maintenance Page 15 AT-502A/502B/504 March 14, 2018 The counterweight support tube is p/n 20279-1 and can be removed from the aileron by removing the two plug buttons on the upper and lower side of the aileron nose skin and removing the AN3-12A bolt that attaches the support tube to the support structure that is riveted to the aileron.

  • Page 35: Aileron And Flap Rigging

    Maintenance Page 16 Air Tractor, Inc. March 14, 2018 AT502A/502B/504 AILERON AND FLAP RIGGING With the flap actuator in the “Up” position, the flap push-rods are adjusted so that the lower side of the flaps form a straight line with the lower side of the fuel tank at station 61.0. Flap travel from this point is then...

  • Page 36: Flap Actuator

    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.

  • Page 37: Flap Actuator Troubleshooting

    The actuator assembly has a threaded collar. This collar is threaded internally to match the threads on the worm drive threads of the actuator, and is threaded externally to match the threads of the Air Tractor “Tee” assembly which is p/n 70037-1. The “Tee” assembly is attached to the two 1/4" aluminum 70032-1 arm assemblies that are bolted to the flap torque tube assembly.

  • Page 38: Flap Actuator Removal Instructions

    Air Tractor, Inc. Maintenance Page 19 AT-502A/502B/504 March 14, 2018 See drawing 60198 for flap system wiring schematic. The actuator jack screw is fitted with a stop to mechanically limit the ball nut travel in case of a problem with the down microswitch or relay. If you replace the actuator, the new one will come with a new stop nut.

  • Page 39: Flap Motor Troubleshooting

    Maintenance Page 20 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 6. Re-check the position of the UP micro-switch two ways: Raise the flaps all the way with the flap switch. After the flaps are fully retracted continue to hold the flap switch up and observe the voltmeter. If the voltmeter shows excessive voltage drop, the micro-switch has not turned off the current.

  • Page 40: Stabilizer Struts

    Air Tractor, Inc. Maintenance Page 21 AT-502A/502B/504 March 14, 2018 Stabilizer Struts The stabilizer struts attach to the fuselage frame with a AN6C11A bolt and to the stabilizer eyebolts with AN6-11A bolts. There are p/n 30256-1 stainless terminals with AN316C8 check nuts at each strut end to allow for adjustment.

  • Page 41: Rudder

    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.

  • Page 42: Elevators

    Air Tractor, Inc. Maintenance Page 23 AT-502A/502B/504 March 14, 2018 The rudder pedal castings are p/n 70115-1 (L/H) and 70115-2 (R/H) and may be removed by taking out the AN3 bolt though the p/n 1SC Caplug on the inboard end of the hanger assembly and removing the AN4-10 bolt attaching the master cylinder strap.

  • Page 43: Elevator Control

    +/-1 ELEVATOR CONTROLS The aft elevator push-rod that connects to the elevator horns is p/n 70020-1 (AT-502A/502B) or 71783- 7 (504) and is adjustable on the forward end which has a Fafnir RE4M6 bearing installed. The aft end of the push-rod has a NMB p/n ABT4 bearing same as the elevators and rudder and is pressed into place and staked same as in other applications.

  • Page 44: Cockpit Controls

    The control stick assembly (p/n 70346-1 for the AT-502A/502B, 2 each of p/n 70346-16 for the AT- 504) is attached to the torque tube assembly (p/n 70050-7 for the AT-502A/502B, 2 each of p/n 71953-1 for the AT-504) with an NAS1304-44 bolt. The lower end of the control stick is a machined aluminum part (p/n 70043-1) which houses two Fafnir KP4 bearings held in place by two p/n 1300-93 snap rings.

  • Page 45: Elevator Trim Tabs

    80131-1 boot with p/n 70154-1 boot ring. The trim pushrod has a p/n 70070-1 boot and a p/n 70143-1 boot ring. A control lock assembly (p/n 70748-1 for the AT-502A/502B and p/n 71982-1 for the AT-504) is attached to two AN42B-4A eyebolts that are part of the instrument panel attachment. An Ajax No. 38 spring keeps the control lock pulled up out of the way.

  • Page 46: Trim Lever

    TRIM LEVER The trim lever is p/n p/n 71362-2 for AT-502A/502B or p/n 71362-4 for AT-504. It has a p/n 70453-1 stop installed with slotted holes that allow movement up and down to adjust the tab travel. To position the lever in neutral, install the control lock, position the lever in the green band, and adjust the forward push-rod until the trim tabs are lined up with the elevator trailing edge.

  • Page 47: Fuselage Cockpit Skins

    Maintenance Page 28 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 FUSELAGE COCKPIT SKINS The cockpit skins are riveted to the floor and to the support angles with MS20470AD4 rivets. Attachments to the door frames are CR163-4-4 Cherry rivets. The cockpit skins may be removed by drilling out the rivets where necessary and is not a difficult operation.

  • Page 48: Engine Driven Air Conditioner

    AmSafe Authorized Service Center. ENGINE-DRIVEN AIR CONDITIONER All Air Tractor aircraft use a gas-cycle air conditioning system for climate control. The air conditioning system lets the pilot select ram air from outside, re-circulate cockpit air, or a mix of the two. The ram-air control handle location is on the aft-cockpit wall on the RH side of the pilot.

  • Page 49: Cautionary Information

    Maintenance Page 30 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Cautionary Information A. Pressure Release • Before disconnecting any lines or removing the oil plug, always make sure refrigerant has been removed from the air conditioning system by recovering it with the appropriate recovery equipment.
  • Page 50 Air Tractor, Inc. Maintenance Page 31 AT-502A/502B/504 March 14, 2018 Never mix R134a with other refrigerants or air conditioning systems failure may to occur. Use only Sanden specified PAG lubricants for R134a systems using Sanden compressors. If other lubricants are used, air conditioning system failure is likely to occur.

  • Page 51: Application Specifications

    Maintenance Page 32 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Application Specifications A. Oil Flow Theory • Compressor lubrication occurs as the oil which circulates with the refrigerant passes through the compressor crankcase during operation. The Sanden SD series compressor achieves optimal durability and cooling performance when oil circulates through the system at a ratio of 3.3% to 8% oil to refrigerant.
  • Page 52 Air Tractor, Inc. Maintenance Page 33 AT-502A/502B/504 March 14, 2018 B. Clutch Inspection Voltage Check • Confirm that the clutch is receiving at a 12 Volts minimum11.5 V or 23 V for 12 V and 24 V systems respectively. If voltage is not being received at the clutch run a diagnostic on the vehicle electrical system.
  • Page 53 350 psig it is a good compressor. Important: This test must be performed with a full system charge! Confirm the system is charged per Air Tractor requirements in this section before proceeding. Disconnect electric cooling fan. The condenser can also be blocked with sheet of card board.
  • Page 54 Air Tractor, Inc. Maintenance Page 35 AT-502A/502B/504 March 14, 2018 E. Noise Unusual Noise Not due to Compressor Unusual noises may be caused by components other than the compressor Compressor Mounting - Check for: • Loose belt - see belt tension specifications.

  • Page 55: Compressor Repair

    Maintenance Page 36 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Compressor Repair Clutch Components 1. Armature dust 7. Pulley & Bearing 4. Armature plate 10. Field Coil cover screw Snap Ring 2. Armature dust 8. Pulley & Bearing 5. Clutch Shims...
  • Page 56 Air Tractor, Inc. Maintenance Page 37 AT-502A/502B/504 March 14, 2018 Spline Shaft Armature-Removal • The spline shaft armature will not have threaded holes to accept the armature puller • Lift off armature plate with fingers. If armature does not come off easily, spray an anti seizes oil into shaft to loosen.
  • Page 57 Maintenance Page 38 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 B. Clutch Replacement Field Coil Assembly Installation • Reverse the steps of the previous section. Protrusion on underside of coil ring must match hole in front housing to prevent movement and correctly locate lead wire(s).
  • Page 58 Air Tractor, Inc. Maintenance Page 39 AT-502A/502B/504 March 14, 2018 Armature Retaining Nut • Replace retaining nut and torque to specification. 1/2-20: 20- 25 ft•lb (27-34 N•m, 270-350 kg•cm) M8: 11-15 ft•lb (15-21 N•m, 150-210 kgf•cm) Air Gap Conformation •...

  • Page 59: Compressor Replacement

    Maintenance Page 40 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Compressor Replacement  It’s critical for successful compressor replacement that the new compressor is installed in a clean system with a correct oil charge. Contamination remaining in the system will be pulled into the new compressor and lodge under the valves and in bearings causing quick failure of the new compressor.

  • Page 60: Service Procedures

    Air Tractor, Inc. Maintenance Page 41 AT-502A/502B/504 March 14, 2018 C. Oil Amount (Compressor swap, no flushing) • The goal of this procedure is to measure the oil amount in the failed compressor and adjust the amount in the new compressor to equal that of the failed Remove the oil plug from the failed compressor and drain as much oil as possible into a suitable container.
  • Page 61 Maintenance Page 42 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Components to Flush • Flush hoses, hard lines and heat exchangers. DO NOT flush the compressor, accumulator or receiver drier, refrigerant lines with mufflers, thermal expansion valve or orifice tube because residual flushing fluid cannot be removed from these components and they restrict the flow of flushing agent through other components.
  • Page 62 Air Tractor, Inc. Maintenance Page 43 AT-502A/502B/504 March 14, 2018 Explanation of Evacuation Water Boils Under a Vacuum  As vacuum is increased the temperature at System Vacuum Boiling Point which water boils drops. As the water/moisture Inches Mercury Degrees F boils its vapor can be drawn out of the system 24.04”...
  • Page 63 Maintenance Page 44 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 2. Through the low side with the system running.  With the engine running at flight-idle speed (approximately 75 percent Ng) with the propeller in the feathered position. The air conditioner master switch is turned ON. The...
  • Page 64 Air Tractor, Inc. Maintenance Page 45 AT-502A/502B/504 March 14, 2018 System Oil Amount  Oil circulates with the refrigerant during operation. During off periods oil will settle in all system components with more collecting in cool components like evaporators, accumulator and suction lines.

  • Page 65: Common Causes Of Compressor Failure

    Maintenance Page 46 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Example A large system with no leak requires new compressor, suction hose and Note: compressors drier. delivered with full oil charge. It will be necessary to add or subtract Drain oil from old compressor...

  • Page 66: Hopper

    Air Tractor, Inc. Maintenance Page 47 AT-502A/502B/504 March 14, 2018 A. Clutch Slippage  The compressor clutch is simply two friction surfaces forced together, like a set of brakes. Each time the clutch is engaged some amount heat is generated. If the engagements occur...

  • Page 67: Hopper Lid

    AT-504 uses two each AN4-14A bolts. The bellcrank has two Fafnir KP6A bearings with a p/n 70091-2 spacer bushing that allows the bolt to be fully torqued. The bellcrank is p/n 80068-1 for AT-502A/502B, p/n 83407-1 for AT-504 and has a p/n 80132-1 boot, 70140-1 boot ring attached to the lower fuselage skin with 90013-4 screws, MS21044CO8 nuts.

  • Page 68: Spray Plumbing

    Air Tractor, Inc. Maintenance Page 49 AT-502A/502B/504 March 14, 2018 SPRAY PLUMBING The plumbing from the hopper gate box to the spray pump consists of a p/n 80385-1 tube assembly with a p/n 22899 coupler attached to the gate box and a 80376-1 hose attached to the 80385-1 tube. The hose is clamped with 200-56S clamps which are entirely stainless.

  • Page 69: Stripping And Re-Painting Parts

    Maintenance Page 50 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 STRIPPING AND RE-PAINTING PARTS Stripping and Re-painting Aluminum Parts 1. The paint stripper most effective on urethane paint is Turco #5351. 2. The stripper is either sprayed on with a barrel pump or applied on small parts with a large paint brush. If sprayed on be sure to consider wind direction so that over-spray will not damage surrounding vehicles or aircraft.

  • Page 70: Priming Aluminum Parts With Chromated Alkyd Primer

    Air Tractor, Inc. Maintenance Page 51 AT-502A/502B/504 March 14, 2018 9. 9. Full cure is achieved after approximately 18 hours of air dry. 9.10. If parts are allowed to dry in excess of 48 hours before topcoat application, they must be sanded and reprimed.

  • Page 71: Materials Used For Stripping, Painting, & Preservation

    Maintenance Page 52 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Materials Used for Stripping, Painting, and Preservation Urethane Topcoat Materials At the time of this writing the factory uses materials produced by the PRC Desoto Aerospace Coatings. High Solids Epoxy Primer on Aluminum Parts Desoprime (TM) HS CA 7700/CA 7755 (with BE activator) by PRC DeSoto Aerospace Coatings.

  • Page 72: Torque Values For Shop Use

    Air Tractor, Inc. Maintenance Page 53 AT-502A/502B/504 March 14, 2018 TORQUE VALUES FOR SHOP USE Torque Value (i n ch-pounds) Si z e of Nut or Bol t Tension Type Nuts Shear T ype Nuts 1032 60-70 20-25 1/4-28 100-120...

  • Page 73: Electrical System

    Each of the separate electrical circuits discussed in this section is accompanied by its particular wiring schematic drawing. In most cases, the Air Tractor drawing number of a component is shown in parentheses on the schematic drawing. The associated Air Tractor part number of a component is the drawing number plus "-1”...

  • Page 74: Charging System Troubleshooting Guide

    Air Tractor, Inc. Maintenance Page 55 AT-502A/502B/504 March 14, 2018 Charging System Troubleshooting Guide GENERAL CONSIDERATIONS - As a general rule if the Starter Generator functions normally in the Start mode there will be nothing wrong with it that would prevent it from functioning in the Generate mode.

  • Page 75: Troubleshooting Procedures

    Maintenance Page 56 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Troubleshooting Procedures Static Tests - Before going into specific Symptoms which will result in operational “squawks” it is productive to point out a static test routine that is “quick and easy” and will result in localizing some problems without starting the engine.
  • Page 76 Air Tractor, Inc. Maintenance Page 57 AT-502A/502B/504 March 14, 2018 Troubleshooting Procedures (Cont.): Symptom - After an engine start the Generator won’t come on line (low VM reading and/or LV Lite “ON”) but normal generator output voltage exists (nominally 28V) at A1 of the LCR.

  • Page 77: Lighting System Troubleshooting

    Maintenance Page 58 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Lighting System Troubleshooting Electronic Instrument Light Dimmer Description The instrument lights are dimmed by two separate dimmer controls. One of these is for the upper panel instrument lights and the other is for the lower panel lights. The instrument light switch feeds power to the dimmer circuits and the flap light through the five Amp instrument-light circuit breaker.

  • Page 78: Checking The Batteries

    Air Tractor, Inc. Maintenance Page 59 AT-502A/502B/504 March 14, 2018 “B” terminal, the variable resistor (P/N RV4NAYSD-102A) is bad or has a bad ground. If the voltages to the “B” and “C” terminals of the transistor are good and the dimmer does not work, the transistor is bad. To install a new transistor (P/N 2N3055), coat the bottom of the transistor with a thin coat of heat-sink compound.

  • Page 79: Oil Cooler Blower

    Maintenance Page 60 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 in a cell indicates a bad cell. Replace the battery if it fails to meet this requirement. If the battery passes this test, recharge it before returning it to service.

  • Page 80: Wing Flaps

    Air Tractor, Inc. Maintenance Page 61 AT-502A/502B/504 March 14, 2018 Wing Flaps The wiring schematic for the wing flaps is shown in Drawing 60198. Power to drive the flaps up and down is provided by the cockpit flap switch. The wiring from the flap switch is routed through the micro- switches that serve as limit switches for the full "ON"...

  • Page 81: Position & Strobe Lighting

    Maintenance Page 62 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 Position and Strobe Lighting The wiring schematic for the position lights and the strobe lights is shown in Drawing 60059. These lights are controlled by the navigation-light switch on the lower instrument panel. When the switch is placed in the “DOWN”...

  • Page 82: Avionics

    504-4001. Air Tractor Recommendations: Air Tractor Service Letters are used to communicate field experience that may be helpful to the owner of the airplane. Some of these service letters recommend the retirement of certain parts after they have been in operation for a given period of time.

  • Page 83: Propeller Maintenance

    Maintenance Page 64 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 The recommended landing-gear bolt replacement times for the 502A/502B/504 are shown below in accordance with Service Letter 117. RECOMMENDED LANDING GEAR BOLT REPLACEMENT TIMES Bolt Location Bolt Size Bolt Life...

  • Page 84: Tie-Down Instructions

    This check should be made at 100-hour intervals as called out in the Inspection Section. TIE-DOWN INSTRUCTIONS To help protect against damage from strong or gusty winds when parked, your Air Tractor airplane should be tied down to ground tie-down facilities using lines made of nylon rope, vinyl-covered chain or cable, or nylon webbing.

  • Page 85: Towing Instructions And Limitations

    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).

  • Page 86: Draining The Static System

    March 14, 2018 DRAINING THE STATIC SYSTEM The static ports on the AT-502A/502B are the low points of the system and are normally self- draining. There are "T" fittings on the rear face of the static-port buttons. The downward-facing arm of the "T"...

  • Page 87: Leveling

    TT1200 Turbine Temperature Test Set. Other ITT calibration equipment may be used if that equipment is appropriate for use with Air Tractor ITT systems. When other equipment is used, the operator shall follow the manufacturer’s operating instructions. Ensure that the test equipment has a current calibration before performing a calibration check of the engine instrument.
  • Page 88 Air Tractor, Inc. Maintenance Page 69 AT-502A/502B/504 March 14, 2018 Most aircraft manufactured after mid-2000 have an ITT instrument without lead resistance. These systems will not provide a temperature indication unless the indicator is powered with 24 to 28 volts, or normal aircraft power.
  • Page 89 Maintenance Page 70 Air Tractor, Inc. March 14, 2018 AT-502A/502B/504 SYSTEMS WITH LEAD RESISTANCE (Power NOT Required) 1. Aircraft power should be OFF during this procedure. 2. Disconnect the leads from the back of the instrument in the cockpit. Note which lead connects to which terminal.
  • Page 90 Air Tractor, Inc. Maintenance Page 71 AT-502A/502B/504 March 14, 2018 Engine Model Tolerances Line Triangle 200°C to 700°C 700°C to 810°C Beyond 810°C Varies 1090°C PT6A-15, -21, -27, -28, -34, -36 + 10°C + 5°C + 10°C + 10°C + 10°C Series 100°C to 865°C...
  • Page 91 This Page Intentionally Left Blank...

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