The student pilot was on final approach to the Florida Flying Gators Ultralight Airport (3FD4) in Minneola, Florida, when the Plante Challenger II “abruptly” turned right 45° and the flight controls no longer felt normal.
He added power to go-around, but 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 hit terrain, resulting in substantial damage to the fuselage and both wings. The pilot was seriously injured in the crash.
A post-accident 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 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 the tensioner reaches the desired parameters and also adhere to the manufacturers recommended life limits and inspection cycles.”
Probable Cause: Failure of the engine/propeller drive belt.
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This January 2021 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
