ERA21LA109

The pilot of the experimental amateur-built airplane stated that he was on final approach when the airplane “abruptly” turned right 45°, and the flight controls no longer felt normal. The pilot said it was a challenge to maneuver the airplane and, as he attempted to avoid trees, the airplane stalled and impacted the ground. A postaccident examination of the airplane and its two-stroke engine revealed that the belt that connected the engine output sprocket to the propeller drive sprocket had broken. The belt had not been manufactured for use in aircraft. Examination of the edges of the belt revealed that it appeared rubbed with exposed core strands in several areas consistent with lateral travel or tracking and that the belt ultimately broke due to tensile overload failure.

On January 21, 2021, about 0945 eastern standard time, an experimental amateur-built Challenger II, N4469Z, was substantially damaged when it was involved in an accident near the Florida Flying Gators Ultralight Airport (3FD4), Minneola, Florida. The student pilot/owner was seriously injured. The airplane was operating as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot stated that he was on final approach when the airplane “abruptly” turned right 45° and the flight controls no longer felt normal. He added power to go around and immediately decided it was best to make a forced landing in a field east of the airport, and reduced power. The pilot said it was a challenge to maneuver the airplane and, in an attempt, to avoid trees, the airplane stalled. It then impacted terrain, resulting in substantial damage to the fuselage and both wings. A postaccident examination of the airplane and its two-stroke engine revealed that the belt that connected the engine output sprocket to the propeller drive sprocket was broken and laying across the empennage. Detailed examination of the belt revealed that it had a transverse fracture that intersected a tooth root at the interior side and had a more jagged transverse path through the glass reinforcement core strands, features consistent with a tensile overload failure. The edges of the belt appeared rubbed with exposed core strands in several areas consistent with lateral travel or tracking. The interior surfaces of the drive belt generally appeared free of significant wear, though fiber damage was observed on the interior surface where the tooth peaks were damaged on approximately 12 of the 120 total teeth. The pilot purchased the airplane in October 2020. He said that the previous owner had installed the belt. The pilot estimated the belt had accrued about 70 hours when it failed. Markings on the exterior surface of the belt indicated the belt was a PowerGrip GT3 960-8MGT-50 synchronous belt manufactured by the Gates Corporation. The Gates PowerGrip GT3 Drive Design Manual includes a “Safety Policy” for primary in-flight aircraft systems that states, “Do not use Gates belts, pulleys or sprockets on aircraft, propeller or rotor drive systems or in-flight accessory drives. Gates belt drive systems are not intended for aircraft use.” In June 2015, the Federal Aviation Administration (FAA) issued an InFO (Information for Operators) bulletin (No. 15007), titled Gates Products Not Designed or Intended for Aircraft Use. It stated: Operators and repair facilities should familiarize themselves with the information contained within this InFO and with Gates Catalog Aircraft Policy in order to be aware of and reduce the risk of accidents caused by belts not intended for aircraft use. However, if Gates products are used, operators and repair facilities should be aware of main drive belt breaks on aircraft utilizing a hydraulic cog belt tensioner and the proper measurement of tension when thetensioner reaches the desired parameters and also adhere to the manufacturers recommended life limits and inspection cycles.