What happened
On August 26, 2013, a Robinson R44 helicopter, registration SE-JOE, was conducting a water sampling mission for the Stockholm County Administrative Board. The aircraft, operated by Eastair AB, was flying over the Tyresö-Flaten lake in Sweden to collect samples from various bodies of water. To facilitate the sampling process, the rear left door had been removed, and the crew was equipped with life jackets and emergency pop-out floats.
As the pilot approached the lake, the water surface was extremely calm, creating a condition known as "bleke," which lacks visual texture. The pilot noted the difficulty in estimating the altitude above the water and intentionally reduced the rate of descent, hoping to create surface disturbances with the rotor wash to establish a height reference. While attempting to maneuver to stop the descent at an estimated height of 5 to 10 meters, the helicopter struck the water surface. The impact caused the stabilizer to hit the water, breaking parts of the tail boom attachment, followed by the main rotor and fuselage hitting the lake. The aircraft subsequently overturned, though the emergency floats deployed and allowed the crew to evacuate through the open door area.
The investigation
The Swedish Accident Investigation Authority (SHK) conducted a technical examination of the aircraft and interviewed the pilot, the crew member, and witnesses. The investigation focused on the pilot's ability to maintain altitude and the lack of visual references during the approach. Investigators also reviewed the aircraft's equipment and the operator's procedures.
Findings
- The primary cause of the accident was the loss of control over the closing speed and distance to the water surface due to the lack of visual references.
- The calm water conditions created a lack of visual texture, making it nearly impossible to accurately judge the altitude.
- The aircraft was not equipped with a radar altimeter, which could have provided the necessary height data.
- The operator's manual lacked specific procedures for approaching or hovering over calm water surfaces when visual references are unavailable.
- There were no technical malfunctions identified in the helicopter prior to the impact.