Accident Overview
On June 2, 2023, at approximately 1450 central daylight time, a Kolb Twinstar Mark III airplane, registration N1025T, sustained substantial damage in an accident near Starbuck, Minnesota. The flight instructor and the private pilot onboard received serious injuries. The aircraft was being operated as a Title 14 Code of Federal Regulations Part 91 instructional flight.
Preflight and Flight
The private pilot, who also owned and built the experimental airplane, intended to practice soft field landings in the tailwheel-equipped aircraft. Before departure, the pilot topped off the fuel and conducted a preflight inspection, noting no anomalies. Additionally, the flight instructor and pilot reviewed meteorological data and observed no concerns. The airplane departed from Chandler Field Airport (AXN) in Alexandria, Minnesota, at about 1409, heading to Starbuck Municipal Airport (D32) in Starbuck, Minnesota.
Landing and Accident
Upon arrival at D32, the airplane entered the traffic pattern and completed two three-point landings on the dry turf of runway 15. During the third landing, with the pilot at the controls, the left wheel separated from the left strut at touchdown. The airplane slid across the turf and nosed over, coming to rest inverted. Both occupants egressed without further incident.
Postaccident Examination
The accident resulted in substantial damage to the fuselage, both wings, and the empennage. The aircraft was equipped with an ASR-Pioneer airframe parachute system, which did not activate during the sequence. The pilot reported that the turf runway was in "great shape" and that a postaccident inspection found no holes or ruts. A metallurgical examination of the left main landing gear revealed that the left axle fractured from bending overstress, consistent with upward and outward forces on the wheel. The axle's chemical composition matched Type 4130 alloy steel, and its hardness was consistent with typical tensile strengths for that alloy. No metallurgical deficiencies were identified.
Additional Information
The Federal Aviation Administration's Airplane Flying Handbook (FAA-H-8083-3C) includes guidance for soft field landings in tailwheel-equipped airplanes, describing techniques such as touching down the tailwheel simultaneously with or just before the main wheels and holding back-elevator pressure to minimize nose-over tendency and provide aerodynamic braking.