What happened
On September 8, 2018, an ASSO 4 Whisky ultralight aircraft, registration OK-SAL 05, was performing a navigational flight from Náchod to Teplice as part of a group of three aircraft. While approaching the Teplice airfield (LKTEPL) on a landing pattern for runway 36, the pilot initiated a left-hand turn at a low altitude, approximately 150 to 200 meters above the ground. During this maneuver, the aircraft entered a left-hand spin and continued descending until it struck a field approximately 1.3 km north of the village of Zábrušany. The impact was followed by a post-crash fire that destroyed the aircraft. The pilot sustained fatal injuries.
The investigation
The ÚZPLN investigation examined the aircraft's mechanical condition, the pilot's experience, and the prevailing meteorological conditions. Investigators analyzed the engine and fuel system, noting that the fuel selector switch was set to the left wing tank. Expert analysis of the Rotax 912 ULS engine confirmed that the engine had ceased operating prior to impact. The investigation also reviewed witness statements, which indicated that the pilot had been in a hurry during pre-flight preparations and had experienced significant turbulence and headwind/tailwind fluctuations while flying over a nearby quarry. Medical examinations of the pilot found no evidence of an acute medical emergency as the cause of the accident.
Findings
- The pilot was performing a high-bank turn at low airspeed and low altitude.
- The engine failure, likely caused by fuel starvation from the left wing tank, occurred during the critical phase of flight.
- Turbulent atmospheric conditions and a significant tailwind component contributed to a reduction in indicated airspeed (IAS) during the turn.
- The pilot had limited flight experience on this specific aircraft type.
- Pre-flight preparations were conducted in haste, which may have resulted in inadequate flight planning regarding the weather conditions.
- The aircraft's fuel system design required manual switching between wing tanks, and the selector was found in the left tank position.