What happened
On January 31, 2000, a Dromader M18 aircraft, registered ZS-NLR, was engaged in agricultural spraying operations near Grootvlei. Following the completion of five spraying passes, the pilot paused the operation to refuel and replenish chemical supplies. While the aircraft was idling at approximately 600-700 rpm, the pilot engaged in a conversation with a local farmer.
Upon attempting to depart, the engine failed to reach the necessary power levels for a standard takeoff. This lack of thrust forced the pilot to perform an emergency landing. During the descent and subsequent impact, the left undercarriage of the aircraft detached from the airframe.
The investigation
Investigators examined the aircraft at the accident site to determine why the engine failed to produce full power during the takeoff roll. A ground run of the engine was conducted at the scene, which revealed that the engine was functioning without any apparent mechanical issues or malfunctions under testing conditions.
Findings
- The primary factor in the power loss was related to the engine's operational state during the preceding idle period.
- Excessive oil accumulation on the bottom spark plugs is a known characteristic of this radial engine type when operating at low RPM.
- The buildup of oil on the plugs during the period the aircraft was idling prevented the engine from generating full power during the takeoff attempt.