What happened
On November 14, 2010, a CH-7 Kompress helicopter, registration OK-JHA10, was performing a VFR flight from Hradešín to Bohuňovice for a scheduled inspection. The pilot had been in contact with the Čáslav Tower (TWR) earlier in the flight, reporting his position and altitude without incident.
As the aircraft progressed toward its destination, witnesses near the village of Březové observed the helicopter flying at a low altitude. Witnesses reported hearing a loud, hollow bang, after which a small part of the aircraft detached. The helicopter immediately entered a rapid spin and descended toward the ground. Other witnesses near the Náklo quarry noted a change in the engine sound, describing a sudden increase in pitch followed by a decrease in RPM. The aircraft struck the ground near the edge of a quarry, resulting in the fatal injury of the pilot and the total destruction of the aircraft.
The investigation
The ÚZPLN investigation focused on the structural integrity of the aircraft and the sequence of events leading to the loss of control. Investigators examined the wreckage and recovered components, including parts of the tail boom and the tail rotor assembly. The investigation also reviewed maintenance records and compared the maintenance procedures used in the Czech Republic with those used by the manufacturer in Italy, noting differences in how tail rotor blades were inspected.
Findings
- The investigation established that a tail rotor blade failure occurred during flight.
- A portion of the tail rotor assembly detached from the aircraft, causing the helicopter to lose directional stability and enter an uncontrollable spin.
- Evidence from the wreckage showed impact marks where the main rotor blades struck the tail boom, consistent with a loss of tail rotor effectiveness.
- Fatigue cracks were identified on the tail rotor blades examined during the investigation.
- Maintenance practices for tail rotor blades varied between the local service center and the manufacturer, with the local center not dismounting the blades for inspection.