What happened
The pilot reported that shortly after takeoff, dense white smoke began to fill the cockpit, appearing to originate from beneath the instrument panel. Although the aircraft instruments indicated normal operating ranges, visibility inside the cabin rapidly deteriorated to just a few inches. The passenger in the right front seat, who was also a pilot, assisted in navigating the aircraft back to the airport. The crew executed a landing on runway 20 downwind. Immediately after touchdown, the nose gear collapsed.
The investigation
A post-accident examination revealed that a turbocharger exhaust coupling had failed. This failure allowed hot exhaust gases to escape into the engine compartment. An oil pressure hose line melted due to the heat, spraying oil onto the turbocharger where it mixed with the hot gases and ignited. The resulting smoke entered the cockpit through the vent located beneath the instrument panel. Further inspection of the nose gear showed that the gear down lock springs had been damaged by the fire, which permitted the nose gear to collapse.
Findings
The primary contributing factor was the failure of the turbocharger exhaust coupling. This mechanical failure led to an engine compartment fire caused by oil contacting hot exhaust gases. The resulting smoke obscured visibility, and the fire damage compromised the structural integrity of the nose gear down lock mechanism.