What happened
On the evening of November 6, 2020, an Airbus Helicopters EC135 P3, registration LN-OOZ, was performing a Helicopter Emergency Medical Service (HEMS) flight from the outskirts of Slagelse to its home base at Ringsted (EKRS). The crew, consisting of a commander and a technical crew member, was conducting a night visual approach to runway 23.
As the helicopter reached short final, it unexpectedly entered Instrument Meteorological Conditions (IMC) after encountering low-lying fog and fog patches. The aircraft descended into a field northeast of the aerodrome, resulting in a controlled flight into terrain (CFIT). Following the impact, the crew initiated a go-around procedure. Although the application of power did not immediately arrest the descent, the helicopter became airborne again, allowing the crew to regain control and divert to Slagelse Hospital (EKSE) without further incident.
The investigation
The Danish Accident Investigation Board examined several factors contributing to the impact, including the pre-flight weather briefing, the crew's use of Night Vision Goggles (NVG), and the operational decision-making process. The investigation reviewed meteorological data, including satellite imagery and the UK Met Office Night Illumination Model, to understand the visibility conditions at the time of the accident. The board also analyzed the crew's performance and the technical limitations of NVG during low-altitude operations in foggy environments.
Findings
- The flight crew failed to adequately identify the threat posed by low visibility and fog during the pre-flight phase.
- A decision to fly a shallow approach path placed the aircraft at a lower altitude than the existing ground fog.
- The use of Night Vision Goggles (NVG) made it difficult for the crew to accurately assess height and depth.
- Visual illusions and a sudden NVG whiteout at approximately 100 feet caused a loss of situational awareness.
- The suddenness of the encounter caused a startling effect that delayed the initiation of the go-around.
- The aircraft's low forward speed and attitude at the moment of power application prevented the descent from being stopped before the impact occurred.