What happened
On July 9, 2006, at approximately 10:20 UTC, a Tecnam P92 JS, registration OK-RWY, was performing a banner towing operation at an altitude of 150 to 300 meters near the town of Sázava. During the flight, the engine lost power and subsequently stopped. The pilot immediately released the advertising banner to reduce drag and prepared for an emergency landing.
Due to the flight path being positioned closely to populated areas to ensure maximum visibility of the banner, the pilot had very limited options for an emergency landing site. The pilot selected an area used for soil storage located near the banks of the Sázava River. This surface was significantly uneven and filled with potholes. Upon touchdown, the aircraft traveled approximately five meters before the left main landing gear collapsed, followed shortly by the failure of the nose gear.
The aircraft sustained heavy damage, including damage to the engine, propeller, wing, and tail surfaces. The pilot was uninjured, and no other persons were harmed.
The investigation
The ÚZPLN investigation examined the aircraft's maintenance status, the fuel system, and the flight planning. The investigation established that the aircraft's maintenance release was invalid, as the aircraft had exceeded its scheduled inspection interval by thirteen minutes. Additionally, the aircraft was not listed in the operator's operational specification for aerial work.
Regarding the engine failure, investigators found fuel present in the carburetor float chambers. While the automotive gasoline used (BA 95 Natural) met the required technical specifications, the investigation considered the potential for vapor lock. Given the ambient temperatures, which could have reached approximately 37°C, the formation of vapor bubbles in the fuel lines could have interrupted the fuel supply. Although the pilot had access to an electric fuel pump to mitigate such pressure drops, the rapid nature of the failure may have prevented effective intervention.
Findings
- The primary cause of the accident was the pilot's selection of a flight path and altitude that left extremely limited options for an emergency landing site in the event of an engine failure.
- The aircraft was not airworthy at the time of flight due to an expired maintenance inspection interval.
- The landing surface was highly uneven, which directly caused the collapse of the landing gear and subsequent structural damage to the aircraft.
- The use of automotive gasoline in high ambient temperatures may have contributed to engine failure via vapor lock in the fuel system.