What happened
On September 8, 2009, a Robinson R44 Clipper II helicopter was engaged in a mission to collect water samples from the "See Koritzmühle" open-cast mine lake near Laubusch. The flight began at the Cottbus/Neuhausen airfield, where the pilot, accompanied by a client representative and an additional crew member, had previously landed on the lakeshore to load sampling equipment and remove the left doors.
Following the briefing, the pilot restarted the engine and took off at approximately 09:25 local time. The flight plan involved executing a left turn and descending at a low rate to hover over a specific GPS-coordinated point. The pilot intended to maintain a steady descent until the rotor wash created visible waves on the water, allowing for a stable hover at an altitude of one to three feet above the surface. However, before reaching the intended waypoint, the aircraft made contact with the water and subsequently sank.
All three occupants—the pilot and two passengers—were able to exit the submerged wreckage and swim to the shore. While the crew members were wearing life jackets, they had received no specific training regarding underwater egress.
The investigation
The BFU investigation examined the aircraft's condition, the pilot's experience, and the operational procedures of the operator. The investigation included a readout of the Garmin GPSmap-178C Sounder to reconstruct the flight path. The aircraft, which had only 27 hours of total time, was found to be heavily damaged; the rotor blades were bent or broken, the tail boom was separated from the tail rotor assembly, and the right float had been torn from the landing gear.
Findings
- The primary cause of the accident was the unintentional contact with the water surface during a low-altitude hover maneuver.
- The pilot's attempt to maintain a specific orientation based on the GPS display, which was set to a high zoom level and north-oriented, contributed to the difficulty in maintaining altitude.
- Hovering over water surfaces is inherently hazardous due to the lack of optical depth perception and the loss of visual references caused by rotor wash-induced waves.
- The operator lacked formal written procedures for these specific types of water-sampling flights.
- Although the crew was equipped with life jackets, there was no requirement or training for exiting an aircraft from an underwater position.