What happened
On August 19, 2022, an Air Tractor AT-502B, registration PR-FNO, was performing a ferry flight from Francisco de Assis Aerodrome to Pampulha Aerodrome in Belo Horizonte, Brazil. The aircraft, operated by the Minas Gerais Military Fire Department, was being flown by a single pilot.
During the landing phase at Pampulha, the aircraft approached the runway at a speed slightly exceeding the limits prescribed in the flight manual. Upon touchdown, the aircraft bounced two to three times before the main gear settled. The pilot attempted to maintain directional control using the rudder and differential braking while holding the aircraft in a level attitude, intending to lower the tailwheel only after the airspeed had decreased. However, once the tailwheel made contact with the runway, the aircraft became highly unstable. The pilot lost directional control, causing the aircraft to veer to the right and execute a ground loop, which resulted in the fracture of the tailwheel assembly. There were no injuries to the crew and only minor damage to the aircraft.
The investigation
The CENIPA investigation focused on the mechanical behavior of the tailwheel locking system and the pilot's handling of the aircraft. Investigators examined the aircraft's control linkage and found that while the elevator deflection was within limits, the tailwheel unlocking mechanism was engaging prematurely. Specifically, the tailwheel would unlock when the control stick was moved only slightly forward of the neutral position—representing approximately 31% to 44% of the total forward travel.
While the manufacturer's training material prescribes that the tailwheel should only unlock when the control stick is at the full forward stop, the investigation found that the aircraft's manuals lacked specific instructions regarding the exact elevator angle or stick displacement required for engagement. This discrepancy meant that the pilot's efforts to maintain a level attitude during the landing roll may have inadvertently triggered the tailwheel to unlock, compromising directional stability.
Findings
- The pilot was qualified and held all necessary ratings and medical certificates.
- The aircraft was airworthy, with up-to-date maintenance logs and operating within weight and balance limits.
- The landing was unstable, characterized by an excessive approach speed and multiple bounces on the runway.
- The tailwheel unlocked prematurely due to the control stick being moved forward of the neutral position during the landing roll.
- The pilot had limited experience with this specific aircraft model, with only 25.5 hours of flight time.
- The loss of control was driven by the combination of an unstable landing, the pilot's limited model-specific experience, and the vulnerability of the tailwheel locking system.