What happened
On 13 August 2020, a Robinson R44 Raven II helicopter, registration SP-SVW, was conducting a scheduled familiarization flight for a potential student near Sady, Poland. The flight, operated by Salt Aviation Sp. z o.o., departed from Warsaw-Modlin aerodrome to demonstrate various flight maneuvers, including low-altitude flight and off-field landing techniques.
During the flight, the pilot transitioned from the Narew river toward the Vistula river. While flying over the Vistula, the pilot began a descent. The pilot later claimed that at an altitude of approximately 500 ft AGL, the collective lever became blocked, preventing an increase in power to arrest the descent. The helicopter subsequently collided with the water surface at a speed of approximately 76-78 knots. The impact resulted in two serious injuries to the occupants. The aircraft was destroyed in the collision.
The investigation
The PKBWL investigation examined the aircraft's maintenance history, the flight path via radar data, and the pilot's claims regarding mechanical failure. Investigators analyzed the possibility of a collective blockage by reviewing the swashplate, sliding sleeve, and Aft Support Assembly. The investigation also reviewed recent manufacturer safety alerts regarding hydraulic system stiffness to determine if the aircraft was affected.
Findings
- The investigation found no evidence of a mechanical blockage in the flight control system; the aircraft remained fully maneuverable using the cyclic alone.
- The pilot performed the flight at an altitude below the minimum safe height.
- The pilot failed to conduct a proper safety briefing for the candidate regarding emergency procedures.
- The primary cause of the accident was the incorrect estimation of flight height during the descent over the river surface.
- A contributing factor was the decision to perform flight operations below the permissible minimum height.