What happened
On 4 July 2006, a Robin DR30 and-180R, registration HB-EPG, was performing towing operations at Saanen aerodrome. During the third towing flight of the day, the pilot noticed irregular engine performance while reducing power on the approach to runway 26. Despite attempts to rectify the issue using the carburettor pre-heater and throttle adjustments, the engine cut out approximately 1.5 km from the runway threshold.
The pilot executed a successful emergency landing on runway 26. However, while attempting to restart the engine to vacate the runway, a fire ignited underneath the aircraft's fuselage. Although the pilot was able to evacuate safely, the fire spread rapidly, and the aircraft was completely consumed by fire, resulting in the total destruction of the airframe.
The investigation
Investigators examined the engine, the carburettor, and the muffler system. The technical examination of the Precision Airmotive MA-4-5 carburettor revealed significant wear in the float hinge mechanism. Specifically, the clearance in the hinge was 2.5 times greater than that of a new part, allowing excessive lateral and upward movement of the float.
The investigation also reviewed the aircraft's maintenance history. It was noted that the engine had experienced several previous failures, including a fuel leak and an engine cutout, which had led to the carburettor being sent for repair twice in the preceding year. Furthermore, the investigation noted that the operator's maintenance authorization was limited to minor checks and did not technically cover the dismantling and refitting of the carburettor.
Findings
- The engine failure was caused by a malfunction in the carburettor float system, where excessive hinge clearance prevented proper fuel level regulation, leading to an overflow.
- This pre-existing fault in the carburettor system remained undetected despite previous repairs.
- The pilot was not informed of recent engine-related incidents or fuel leaks that had occurred in the days prior to the accident.
- The fire was triggered during restart attempts following the emergency landing.