What happened
On March 14, 2003, at approximately 10:50 UTC, an ultralight helicopter, an Ultraport 496 with registration OK IHA 10, was undergoing ground-based non-flight testing at a company yard in Vestec, Czech Republic. The procedures being performed involved rotor blade balancing.
During the testing, the pilot increased the engine power to maximum. This caused the helicopter to lift off the ground unexpectedly. As the aircraft ascended, it collided with a passenger car (a Škoda Felicia) that was entering the company premises at that moment. The impact caused the helicopter to flip over the vehicle and crash onto the adjacent roadway, where it landed in the middle of a traffic lane. The impact resulted in the total destruction of the helicopter and damage to the vehicle.
The investigation
The ÚZPLN investigation established that the helicopter was experiencing significant vibrations due to an unbalanced rotor, a condition that had previously caused a flight test to be aborted the day before. At the time of the accident, the pilot was simultaneously managing the flight controls and monitoring a VIBREX instrument used to measure vibration levels for the balancing process.
The investigation also noted that the testing was taking place in a fenced yard with approximately 10 employees observing from a distance of about 10 meters. Environmental factors, including wind gusts, were also considered during the analysis of the sequence of events.