ENGINEERING REPORT DATE. This Service Letter is applicable to all models and all serial numbers of Air Tractor aircraft.

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1 WICHITA FS, TEXAS SUBJECT: Rudder Controls Inspection and Maintenance APPLICABILITY: 1 8 This Service Letter is applicable to all models and all serial numbers of Air Tractor aircraft. PURPOSE: The purpose of this Service Letter is to bring urgent attention to several areas of the rudder controls system that have been found to require special inspection and maintenance techniques. Following these techniques and suggestions will help provide good service life and proper operation of the aircraft rudder controls. Failure to properly maintain the rudder control system could result in a dangerous condition that could result in loss of control of the aircraft. Please inspect your aircraft immediately to ensure that the rudder controls are operating properly. Note that this document is not an exhaustive list of all items to inspect and maintain on the rudder controls, nor does it indicate that less attention should be spent on other aircraft systems due to their omission here. INSPECTION: The rudder pedal assemblies are an important part of the rudder control system, but they don t seem to always get the attention that they deserve. Recent inspections of some in-service aircraft have revealed several rudder pedal assemblies that created a dangerous condition due to severe wear from insufficient maintenance. The following items should be checked upon receipt of this Service Letter and at every annual inspection thereafter. These inspections are in addition to the 100 hour inspections listed in the aircraft Owner s Manual.

2 WICHITA FS, TEXAS 2 8 A current production rudder pedal assembly is shown in the pictures on the following page and includes (1) the pedal casting, (2) rudder pedal arm, (3) brake master cylinder installation, (4) hinge bushing, (5) pedal adjustment channels, (6) adjustment pin, and (7) brake pedal strap (shown hidden behind rudder pedal arm). (4) (7) (2) (1) (6) (3) (5) While performing the inspections called out in this Service Letter, it is a good time to go back and read through these existing Service Letters that pertain to the rudder controls and ensure that they have been complied with: SL#20 - Rudder Pedal Support Tube SL#77 - Rudder Cable Inspections SL#156 - Rudder Pedals SL#190 - Rudder Cables SL#199 - Rudder Cables SL#200 - Rudder Cable to Rudder Horn Attach Hardware

3 WICHITA FS, TEXAS DETERMINE TYPE RUDDER PEDAL HINGE POINT: 3 8 Access the upper rudder pedal hinge point. On airplanes with a hinged lower switch/breaker panel, the lower panel can be lowered to provide access to this area. See picture on the following page. There are two types of rudder pedal hinge bushings that have been used. Early Air Tractor s used a bushing that had a 1/2" I.D. and pivoted directly on the 1/2" bolt. Starting in 1999, a new design was introduced that used a 5/8 I.D. bushing with a bronze bearing inside. A grease zerk was also added at this time to provide an easier lubrication point. Air Tractor highly recommends upgrading all aircraft to this new design. This upgrade requires only a few small parts and can typically be done in a reasonably short amount of time. This upgrade will reduce future maintenance requirements on this hinge. Details on this upgrade are provided later in this service letter. Grease Zerk and Upper Hinge Bushing 1/2 Bolt

4 WICHITA FS, TEXAS UPPER HINGE POINT INSPECTIONS/MAINTENANCE: 4 8 1) Inspect that the rudder pedal arm pivots freely on the 1/2 bolt. If the bolt is seized and/or pivots with the rudder pedal arm, accelerated wear will result and will damage the bolt, causing an unsafe condition. A seized bolt should be removed and replaced (p/n ). With the bolt removed, inspect all of the parts that this bolt passed through. If any of the parts exhibit oblonged holes, they should be replaced as well. This would be an excellent time to upgrade the hinge bushing. 2) Lubricate the upper hinge bolt. If the grease zerk is installed, it is easy to add general purpose grease. If there is no zerk installed, a light oil should be applied to the bolt and inside of the bushing. 3) Inspect that the rudder pedal assembly does not have excessive side-to-side play. Measure this side play at the bottom of the pedal assembly. Some play is acceptable, but only if no part of the pedal assembly comes within 1/8 of the hopper when held in its most severe position and accounting for side play. Inspect the hopper footwells for evidence that the pedals have been rubbing on the fiberglass. No amount of hopper contact is acceptable. If excessive side-to-side play or hopper contact is found, the cause should be identified and it should be corrected before further flight. If the rudder pedals come into contact with the hopper footwell, it could cause the rudder pedal to lock and

5 WICHITA FS, TEXAS 5 8 result in loss of control of the aircraft during takeoff or landing. 4) Inspect upper master cylinder attachment. Ensure bolt, nut, and cotter pin are properly installed. Ensure the connection is secure and inspect the condition of the master cylinder attach arms. PEDAL ADJUSTMENT INSPECTIONS/MAINTENANCE: 1) Inspect rudder pedals for full rudder travel. With an observer standing at the rear of the airplane, ensure that someone sitting in the pilot s seat can move the rudder from stop to stop using the rudder pedals. This check should be done for each pedal position, adjusting the rudder pedals to their forwardmost, aft-most, and center positions. For two-seat aircraft, be sure to perform this check with all combinations of pedal positions. For example: check with pilot pedals full forward and co-pilot pedals full forward, then check with pilot pedals full forward and co-pilot pedals full aft, then check with pilot pedals full aft and co-pilot pedals full aft, and so on... On AT-504 aircraft, check for pedal clearance between adjacent sets of pedals. 2) Ensure the rudder pedal return springs keep the rudder cables from going slack. There is no defined cable tension required for the Air Tractor rudder cables. The airflow over the tail provides the rudder centering force. However, a check should be accomplished to make sure the return spring tension is sufficient to keep the cables off the cockpit floor during full rudder travel. Replace the part

6 WICHITA FS, TEXAS 6 8 number spring(s) if necessary. Typically, pedals adjusted full forward is the critical case for this check. 3) When adjusting the pedals for the inspections described above, inspect the condition of the adjustment T-pins. These pins should have no tendency to back out of the pedal assembly. If they come out with little resistance or have any slack, the pins should be replaced with new ones. Check the condition of the spring loaded ball in the end of the pin. Lubricate it with light oil. If the ball has any tendency to stick, the pin should be replaced. These pins are p/n D5-10T- 303 (normal height) or p/n D5-10T-303/MIN D (reduced height). UPGRADING UPPER HINGE BUSHING: For any aircraft manufactured prior to 1999 that do not have the upgraded rudder pedal hinge with the bronze bushing, the rudder pedal arms can be removed from the aircraft and upgraded. Parts list (per pedal): 1 ea. 1/4-28 nut 1 ea bronze bushing 1 ea. MS grease zerk fitting. Drawings and required also. 1) Remove rudder pedal assemblies from the aircraft. Mark the side of the pedal arm that faces the pilot. 2) Review Drawing The 1/4-28 nut is oriented facing the pilot at a 24 angle from horizontal. Drill a 1/4 hole through one wall of the bushing at this 24 angle.

7 WICHITA FS, TEXAS 7 8 3) Center the nut over this drilled hole and weld the nut to the bushing per Drawing Weld the entire perimeter of the nut. Touch up the paint after welding. 4) Per Drawing 70109, carefully drill and ream the hinge bushing to /-.000 diameter. This must be done perpendicular to the rudder pedal arm to ensure proper alignment when reinstalled. 5) Insert the bronze bushing into this reamed hole. The bronze bushing should be longer than the steel hinge bushing. If this requirement is not met, sand or machine both ends of the steel hinge bushing until it is shorter than the bronze bushing. 6) If desired, steps 2 thru 5 can be skipped and new rudder pedal arms purchased. Order p/n (lefthand) or (righthand). 7) Install MS grease zerk per Drawing If the zerk does not point downward when installed, AN or -416L washers can be used between the zerk and the nut to change the clocking of the zerk. 8) Reinstall the rudder pedals in the airplane. Use new bolts when installing. INSPECTION BRAKE PEDAL STRAP: Each rudder/brake pedal is attached to the brake master cylinder with two formed aluminum straps (p/n ). The upper end of these straps connects directly to the plunger on the master cylinder. The lower end connects to the forward side of the rudder pedal casting with an AN4 bolt. Both the straps and the pedal casting have pressfit bronze bushings. Beginning with aircraft built in early 1999, this AN4 bolt was lengthened and also functions as a stop to prevent the rudder pedal from going over-center if it is pulled aft. 1) Inspect for any free play or damage to the straps.

8 WICHITA FS, TEXAS 8 8 2) Inspect the upper strap connection at the master cylinder. - Ensure there is no brake fluid leaking from the master cylinder. - Ensure that the strap connection does not have any appreciable play and that the attaching hardware is tight and secure. - Ensure that the jam nut is tight against the master cylinder clevis. 3) Inspect the lower strap connection. - Ensure that the connection is tight and that there is no sideto-side play or looseness where the bolt goes through the pedal or strap bushings. Replace bolt and/or bronze bushings if wear is found. - Ensure that the bolt, castellated nut, and cotter pin are properly installed. - Inspect rudder pedal casting for cracks, excessive wear, etc