What happened
During flight over mountainous terrain, the pilot encountered horizontal snow squalls while maintaining ground contact for approximately 25 miles. He approached a cloud layer and flew over it at 16,500 feet MSL. As he continued, the engine began running rough. With the outside air temperature at -15 degrees Fahrenheit, which is below the yellow arc on the carburetor air temperature gauge, he was reluctant to use carburetor heat. After switching fuel tanks and magnetos with no improvement, he applied full carburetor heat. The engine continued to run rough and finally stopped.
He entered the clouds and, with no vacuum suction, descended using the needle, ball, and airspeed indicator. He turned into the wind to reduce ground speed. At about 10,000 feet, the aircraft crashed and came to rest in trees. The ELT operated, but the antenna was broken. The pilot made a shelter, remained overnight, and was rescued on the following afternoon.
The investigation
No engine problem was found except that the plastic foam induction air filter contained water when checked.
Findings
The most significant factor was carburetor ice due to cold temperatures and moisture. The pilot's reluctance to use carburetor heat initially contributed to the failure. Survival of the pilot is attributed to his sheltering and subsequent rescue.