What happened
On June 28, 2012, a CH-7 Kompress helicopter, registration OK-MAH18, was performing a flight from Lipovec, Slovakia, to Bohuňovice, Czech Republic, for a scheduled 50-hour maintenance inspection. During the flight, the pilot encountered low cloud cover over a mountainous area east of Štiavnik. While maneuvering to avoid clouds, the pilot heard an unusual noise from the engine compartment and perceived a loss of engine power.
In response to this perceived failure, the pilot immediately transitioned the aircraft into autorotation. During the subsequent descent, the pilot attempted to check the engine power by adjusting the collective lever; however, rapid and ineffective movements of the controls prevented a proper assessment of the engine's performance. The pilot eventually performed a hard landing on a grassy slope near Štiavnik. The impact resulted in the total destruction of the helicopter, though the pilot sustained only minor injuries.
The investigation
The investigation, conducted by the Czech ÚZPLN in cooperation with Slovak authorities, examined the aircraft's wreckage, engine data, and meteorological conditions. Technical inspections of the Rotax 914 Turbo engine and the Rotax Flydata - TCU recording unit revealed that the engine had been operating normally throughout the flight. The investigation also reviewed the pilot's flight experience and the weather conditions at the time of the accident.
Findings
- The pilot's perception of engine power loss was incorrect; the engine was functioning normally prior to the impact.
- The pilot's mistaken belief of engine failure and subsequent improper use of flight controls during the emergency maneuver led to the loss of control.
- The pilot failed to utilize a previous technical stop at LZZI to reassess the deteriorating meteorological conditions.
- Low cloud cover and terrain maneuvering likely caused the pilot to lose spatial orientation, leading to the unusual aircraft attitude that triggered the perceived engine issue.
- The hard landing was exacerbated by the pilot's lack of experience in performing autorotative landings in terrain.