On September 28, 2023, about 1130 central daylight time, an Air Tractor AT-802 airplane, N445HA, was substantially damaged when it was involved in an accident at Herington Regional Airport (HRU), Herington, Kansas. The flight instructor and pilot receiving instruction were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor, who was in the rear seat, stated that during landing as they slowed to 35 to 40 mph, the tailwheel unlocked, and the airplane turned right. The flight instructor applied full left rudder and attempted to apply the left toe brake, but the brake pedal was restricted from moving forward. When left rudder and left brake were applied, the top of the pedal contacted the spray control lever pushrod and full brake could not be applied. The airplane continued off the right side of the runway. The airplane impacted a ditch, which resulted in substantial damage to the wings. Postaccident examination revealed that the front-seat rudder/brake pedals could move through their full range of motion without interference. The rear-seat rudder/brake pedals were found in the forward adjustment position. With the rear pedals in the forward position, the left rear brake pedal range was restricted by the upper spray valve control pushrod, preventing the application of full left brake from the rear seat. There were no other mechanical malfunctions or failures with the airplane that would have precluded normal operation. The upper spray valve push rod was installed in the airframe by Air Tractor during the original production of the airplane. Air Tractor reported that there were 94 other airplanes affected by this design installation. As result of this investigation, on December 29, 2023, Air Tractor completed service letter (SL) 405, which was applicable to certain AT-802 airplanes with a spray valve control lever installed. The SL was issued due to the spray valve control valve pushrod’s interference with the left rear rudder pedal, which reduced controllability and could lead to an accident. The interference was only possible when the left rear rudder pedal is in the forward adjustment position (Figure 1). This interference prevents simultaneous application of full left rudder and left brake when operated from the rear seat. This control restriction could lead to a loss of control causing significant injury and aircraft damage. Placement of the rear rudder pedals in the rear adjustment position is a temporary solution that will allow full, simultaneous application of left rudder and left brake.

Figure 1. Air Tractor photo and labels of the rudder pedal restriction with spray valve control lever pushrod (Courtesy of Air Tractor SL 405). As result of this investigation, on April 25, 2024, the Federal Aviation Administration issued special airworthiness information bulletin (SAIB) 2024-03, “Rudder Control System,” which recommended that all affected operators modify the rear cockpit rudder pedal adjustment in accordance with Air Tractor, Inc. Service Letter 405.