What happened
On February 19, 2017, a Pipistrel Virus SW 80 ultralight aircraft was conducting a private flight under visual flight rules (VFR) from Hodenhagen to Gelnhausen and back. While the initial leg of the flight proceeded without issue, a weather front moved into the area, significantly degrading visibility and cloud ceilings.
During the return leg, the pilot attempted to descend through a gap in the clouds to fly below the main cloud layer, intending to reach Rinteln. However, the descent into lower altitudes led to the encounter with moderate icing on the propeller and the pitot tube. The icing caused the airspeed indicator to become unreliable, forcing the pilot to rely solely on GPS data. As visibility continued to drop, the pilot was unable to detect rising terrain and trees in time. The aircraft struck trees approximately 10 meters above the ground, causing the wings to separate from the fuselage before the wreckage impacted the forest floor. The pilot sustained severe injuries but managed to escape the wreckage independently.
The investigation
The BFU investigation examined radar data, flight recorder information from the aircraft's Dynon system, and meteorological reports from the German Meteorological Service (DWD). The investigation focused on the pilot's decision-making regarding weather, the impact of the advancing cold front, and the technical effects of icing on the aircraft's instruments. Investigators also reviewed the pilot's communications with Bremen Center, noting that the pilot did not report the icing issues to air traffic services.
Findings
- The primary cause of the accident was a collision with obstacles after the pilot entered conditions that no longer supported safe VFR flight.
- The pilot's decision to continue the flight despite marginal weather conditions contributed to the accident.
- The pilot underestimated the risks associated with the restricted visibility caused by low-hanging clouds.
- The aircraft encountered moderate icing due to the high moisture content and low temperatures associated with the passing cold front.
- The pilot's attempt to fly below the cloud layer was made without sufficient visibility to maintain terrain separation.