Yes, October 12, 1997 when he crashed the Long-EZ aircraft he was piloting after it ran out of fuel just off the coast at Pacific Grove, CA.
It is a bit more complex than that. Although an experienced pilot he had only had a brief familiarisation flight in the aircraft, he failed to refuel it and when needed to switch fuel tanks, the previous owner builder had placed the fuel switch in a differnt place to the design where it could be reached by the passenger. It is thought that when Denver twisted in the pilot's seat to reach the fuel switch he jammed his foot on one of the pedals causing the plan to go out of control.
A combination of error, an unsafe design modification, and inexperience on the type of aircraft.