What happened
On November 27, 2009, a Robinson R44 Raven I helicopter, registration OK-STE, was conducting a private VFR flight near Brandov in the Ore Mountains. The pilot had departed from Roudnice nad Labem (LKRO) and was maneuvering to land at a pre-selected clearing in the Waltrovka game reserve.
During the landing approach, the pilot attempted a right-hand turn to position the aircraft into the wind. During this maneuver, the aircraft was struck by a powerful wind gust, which the pilot described as being "blown down." This sudden loss of lift caused the helicopter to descend rapidly. In an attempt to maintain rotor RPM and manage the descent, the pilot increased engine power and then lowered the collective to prevent the rotor from stalling.
Unable to arrest the vertical descent, the pilot performed an emergency landing in the terrain approximately 350 meters from the intended site. During the touchdown, the main rotor blades struck the tops of nearby trees, and the aircraft struck the ground heavily. The pilot was uninjured.
The investigation
The ÚZPLN investigation examined the meteorological conditions, the technical state of the aircraft, and the pilot's decision-making process. Investigators analyzed weather data from the Czech Hydrometeorological Institute, which indicated significant wind speeds in the area, with gusts reaching 40–50 kt. The investigation also reviewed the aircraft's maintenance records and the pilot's flight experience.
Findings
- The pilot underestimated the impact of local meteorological conditions and failed to accurately estimate the wind strength at the landing site.
- The pilot's assessment of the wind direction during the landing turn was inaccurate.
- The terrain profile, characterized by a steep slope on the windward side of the ridge, likely caused an acceleration of the airflow, contributing to the sudden loss of lift.
- The wind gust was the primary factor that triggered the loss of altitude.
- The aircraft sustained damage to the main rotor blade tips, the landing gear skids, and the tail structure.
- There were no mechanical failures identified in the aircraft's systems.