What happened
During a flight intended to demonstrate competency for a multiengine flight instructor certificate, the pilot reported no anomalies throughout the duration of the flight. The landing initially appeared normal; however, during the rollout phase, the gear down and locked light extinguished. Following this, the gear warning horn sounded and the left main landing gear broke off the aircraft. This failure caused the pilot to lose control, resulting in the airplane veering off the runway and colliding with a sign. The pilot was not injured.
The investigation
An examination of the left main landing gear revealed a preexisting fatigue crack located on the trunnion's outer diameter surface, immediately adjacent to the lower fillet radius of the web. This crack had expanded to a width of 1.25 inches prior to the final separation of the trunnion. Records indicated that the aircraft's last annual inspection had been completed approximately 53 flight hours and 1.5 months before the accident.