Incident Overview
Approximately two hours into a visual flight rules cross-country flight, the pilot enriched the mixture after indications of excessive cylinder head and exhaust gas temperatures. This action resulted in a higher fuel burn than originally planned, prompting the pilot to change the flight's destination to a closer airport.
Weather Encounters
While en route to the amended destination, the airplane entered instrument meteorological conditions. A subsequent buildup of ice caused a loss of 100 knots of airspeed as the airplane entered a controlled descent. The pilot executed a 180-degree turn and broke out of the clouds over a valley.
Valley Trapped
During the next 50 minutes, the pilot made several attempts to exit the valley. However, mountain peak obscuration and a thunderstorm prevented him from flying out. With fuel now very close to exhaustion, the pilot elected to land on a two-lane highway.
Landing and Impact
During the landing roll, the airplane veered off the side of the road, impacted a tree, slid backwards through a ditch, and collided with a concrete drainage culvert. The airplane sustained damage to the outboard sections of both wings.
Pilot Actions
The pilot had chosen to enrich the mixture based on temperature indications, leading to higher fuel consumption. Despite changing the destination, the subsequent icing and weather conditions in the valley forced the off-airport landing.