Cessna U206 N932DB accident near Falun, Wisconsin

Probable cause

The pilot experiencing the featureless terrain illusion during the approach which gave the perception that the airplane was at a higher altitude over the glassy water surface than it was, resulting in the airplane impacting the water.

NTSB analysis

The pilot departed in the float-equipped airplane to perform three water and three land landings for currency purposes. During the approach to the glassy surface of the rural freshwater lake, the floats impacted the lake. The pilot reported that a “hard impact” occurred, and the float attachment struts were damaged. During the impact, the pilot believed the airplane was between 20 to 25 ft above the glassy surface of the lake. The airplane came to rest upright, and the pilot was able to egress from the cockpit onto a float. The pilot was then picked up by an individual in a nearby boat. Shortly after, the airplane partially sank, and it came to rest inverted in the lake.

The airplane sustained substantial damage to the fuselage. The pilot reported there were no preimpact mechanical malfunctions or failures with the airframe or the engine that would have precluded normal operation. The pilot further reported that the accident could have been prevented by remembering that it is “almost impossible to judge height above glassy water.” The FAA Aeronautical Information Manual (AIM) discusses various illusions leading to landing errors. The FAA AIM defines the featureless terrain illusion as, “an absence of ground features, as when landing over water, darkened areas, and terrain made featureless by snow, can create the illusion that the aircraft is at a higher altitude than it actually is.”

Text from the NTSB. Open the NTSB docket for CEN25LA211 for the full record.