Accident Overview
On September 28, 2023, at approximately 1130 central daylight time, an Air Tractor AT-802 airplane, registration N445HA, sustained substantial damage during an accident at Herington Regional Airport (HRU) in Herington, Kansas. The flight instructor and the pilot receiving instruction were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as an instructional flight.
Sequence of Events
The flight instructor, seated in the rear, reported that during the landing rollout, as the airplane slowed to between 35 and 40 mph, the tailwheel unlocked and the airplane began to turn right. The instructor applied full left rudder and attempted to apply the left toe brake but found that the brake pedal was restricted from moving forward. When left rudder and left brake were applied together, the top of the pedal contacted the spray control lever pushrod, preventing full brake application. The airplane departed the right side of the runway and impacted a ditch, resulting in substantial damage to the wings.
Postaccident Findings
A 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, which prevented the application of full left brake from the rear seat. No other mechanical malfunctions or failures were found that would have precluded normal operation.
The upper spray valve pushrod was installed by Air Tractor during the original production of the airplane. Air Tractor reported that 94 other airplanes were affected by this design installation.
Corrective Actions
As a result of the investigation, on December 29, 2023, Air Tractor completed Service Letter (SL) 405, applicable to certain AT-802 airplanes with a spray valve control lever installed. The SL addressed the interference of the spray valve control valve pushrod with the left rear rudder pedal, which reduced controllability and could lead to an accident. The interference occurred only when the left rear rudder pedal was in the forward adjustment position, preventing simultaneous full left rudder and left brake application from the rear seat. Placement of the rear rudder pedals in the rear adjustment position was identified as a temporary solution to allow full, simultaneous application of left rudder and left brake.
On April 25, 2024, the Federal Aviation Administration issued Special Airworthiness Information Bulletin (SAIB) 2024-03, “Rudder Control System,” recommending that all affected operators modify the rear cockpit rudder pedal adjustment in accordance with Air Tractor Service Letter 405.