Incident Overview
During an en route flight, the pilot encountered freezing rain and climbed to approximately 3500 feet to remain above all weather. Upon throttling back, the engine began surging and failed to produce sufficient power for level flight. The pilot was aware that the ground elevation in the area ranged from approximately 1700 to 1900 feet MSL.
Descent and Cockpit Actions
As the aircraft descended through 2500 feet, the pilot placed two mailbags on his lap. He dimmed the cockpit lights, turned on the taxi lights and windshield alcohol, and began searching for ground references. Despite these efforts, he did not see the ground until the moment of impact.
Pilot's Belief Regarding Alternate Air Door
The pilot believed that the automatic feature of the alternate air door had malfunctioned or failed. He reported that he and another pilot had previously experienced a similar problem in the same kind of weather conditions. According to reports, the aircraft had once been equipped with a manual control for the alternate air door, but this feature had been removed.
Post-Incident Examination
During a functional check conducted after the incident, the engine operated normally. The alternate air door components were too severely damaged from the impact to be operationally checked.