What happened
On February 6, 2024, a private helicopter flight departed from a private property in the Ilihue sector, near the southern shore of Lago Ranco, Chile. The flight, operated by a private pilot accompanied by three passengers, was intended to travel to the Coique sector. Prior to takeoff, light rain had moistened the clothing of the occupants.
During the initial climb, the aircraft's windshield became completely obscured by condensation. This sudden loss of visibility led the pilot to maneuver closer to the shoreline to regain visual references. However, the degradation of the external view resulted in an inadvertent descent. The Robinson R44 II struck the surface of Lago Ranco approximately 172 meters from the takeoff site and subsequently sank. While the three passengers managed to exit the sinking aircraft and were rescued by nearby boats, the pilot was unable to escape and died from drowning.
The investigation
DGAC Chile examined the environmental conditions, the aircraft's mechanical state, and the cockpit configuration. Investigators analyzed the meteorological data, noting that ambient temperatures ranged between 12°C and 20°C with relative humidity between 70% and 100%. The investigation also reviewed the aircraft's maintenance logs and the cockpit ventilation settings at the time of the accident.
Findings
- The primary cause of the accident was the loss of visual references from inside the cabin, which triggered an inadvertent descent into the water.
- The phenomenon known as "flash fogging" occurred, where high humidity and specific temperature ranges caused rapid condensation on the windshield and plexiglass.
- The cockpit ventilation system was not optimally configured to prevent this; the front ventilation knob was only 65% open, and the door ventilation windows were closed during takeoff.
- The pilot experienced Type I spatial disorientation and a subsequent loss of situational awareness due to the inability to perceive the aircraft's angular and linear position.
- There were no mechanical failures or maintenance deficiencies identified in the aircraft's engine or flight controls.
Safety action
- The investigation recommends that helicopter operators be alerted to the rapid onset of "flash fogging" and evaluate available mitigation methods.
- It is recommended that manufacturers consider updating Pilot Operating Handbooks (POH) to include specific procedures for managing windshield fogging.
- The findings should be used to promote workshops regarding the prevention of spatial disorientation and loss of situational awareness among helicopter crews.