What happened
On 18 November 2018, a DH-82a Tigermoth, registration ZS-BUA, departed from Krugersdorp Aerodrome (FAKR) for local circuit flights. Shortly after takeoff from Runway 08, at an altitude of approximately 150 feet, the engine began running roughly and power decreased from 205 and 0 rpm to 1800 rpm.
Following the power loss, the pilot declared an emergency. Attempting to reach the runway, the pilot executed several turns to the left, suspecting carburetor icing and attempting to clear it by adjusting the throttle. However, the engine power continued to decline, dropping to 1400 rpm during the base leg. Realizing the aircraft could not reach the aerodrome, the pilot performed an emergency landing procedure, cutting the fuel and switching off the magnetos. The aircraft struck rocky terrain, rolling approximately 75 meters before hitting a ridge, and eventually nosed over into an inverted position. The pilot sustained no injuries, though the aircraft suffered substantial damage.
The investigation
The investigation examined the aircraft's maintenance history, the pilot's credentials, and the environmental conditions at the time of the incident. The aircraft had undergone an annual inspection only 4.3 hours prior to the accident. Investigators also reviewed the fuel composition, noting that the aircraft was operating on a mixture of 30% AVGAS and 70% MOGAS.
Findings
- The engine experienced a sudden loss of power during the climb, which the pilot was unable to rectify.
- While the pilot suspected carburetor icing, investigators determined there was only a low probability of icing given the 29°C temperature and the specific altitude.
- The use of MOGAS in the engine was noted as a concern, as UK CAA guidance suggests that unleaded MOGAS containing ethanol can damage Gipsy Major engines, specifically affecting non-metallic components like carburetor floats and seals.
- The specific cause of the engine power loss could not be definitively determined.