What happened
On 17 October 2008, a Tri Cubby aircraft, registration ZU-EUP, was conducting a private proving flight near Nylstroom Aerodrome in Limpopo. While the pilot was leveling off and initiating a left-hand turn at approximately 5,500 feet above ground level, fragments of rubber belting were observed exiting the engine cowling near the port side cylinder heads.
Despite the engine continuing to run at full power, the pilot experienced a sudden loss of thrust. Recognizing the emergency, the pilot identified an open field and executed a forced landing. While the initial touchdown was unevent to, the aircraft traveled roughly 50 meters before the nose landing gear encountered soft sand. This caused the undercarriage to collapse and the aircraft to nose over, resulting in substantial damage to the airframe, including bent wing spars and a damaged main frame. There were no injuries to the pilot.
The investigation
SACCAI ID examined the mechanical state of the aircraft and the circumstances of the landing. The investigation confirmed that the pilot was properly licensed and medically fit. Meteorological conditions were favorable, with clear visibility and light winds.
The investigation focused on the engine's power transmission. Because the engine is connected to the propeller via a drive belt, the loss of thrust was directly linked to the failure of this component. The manufacturer, Micro Wings, subsequently performed rig tests on the pulleys and a replacement belt system. These tests concluded that the failure was caused by the belt being over-tensioned, which prevented it from properly meshing with the pulleys during rotation.
Findings
- The primary cause of the accident was the loss of thrust during flight, which necessitated the emergency landing.
- The aircraft nosed over because the nose wheel collapsed upon encountering soft sandy terrain.
- The drive belt failed due to over-tension.
- The drive belt failed to maintain proper alignment within the drive pulleys during operation.