What happened
The pilot reported that he had flown over a frozen lake to determine the condition of the ice and to look for any cracks prior to landing. No cracks were seen and the airplane landed without incident. While taxiing for takeoff, the airplane's left main landing gear dropped into a crack on the ice and the landing gear separated. The airplane's skis were not installed.
The investigation
The examination of the event focused on the interaction between the aircraft's wheeled landing gear and the frozen lake surface. The pilot had conducted a visual inspection of the ice from the air, identifying no visible fractures before executing the landing. However, during the subsequent ground movement for takeoff, the left main landing gear encountered a hidden fissure in the ice. This structural failure was exacerbated by the absence of skis, which would have distributed the aircraft's weight over a larger surface area and prevented the wheels from penetrating the ice sheet.
Findings
The primary contributing factor was the left main landing gear separation caused by contact with an ice crack. The decision to operate a wheeled aircraft on a frozen water surface without appropriate flotation devices (skis) created a high-risk scenario where minor surface imperfections could lead to mechanical failure. The pilot's visual inspection from the air failed to detect subsurface or small-scale fractures that were sufficient to trap the landing gear during ground operations.