Incident Overview
An aircraft experienced an engine overspeed shortly after takeoff in extremely cold conditions, with the ambient temperature approximately -15 degrees Fahrenheit. The pilot had reported preheating the engine for 30 minutes and indicated that all engine indications were within normal ranges before departure. Shortly after becoming airborne, the engine began to overspeed. The pilot reduced throttle and initiated a turn back toward the airport, but the engine subsequently seized. During the subsequent forced landing, the aircraft stalled at an altitude of about 25 feet above the runway, resulting in damage to the landing gear and wings.
Post-Incident Examination
An examination of the engine revealed a cracked crankcase; no other mechanical failures were identified. The engine had an adequate supply of oil, but analysis of the oil viscosity showed it to be approximately SAE 55. The standard winter operating procedure required the use of a lower viscosity oil and/or an adequate engine warm-up period after engine start.
Weather and Operational Context
The outside air temperature was extremely low, at minus 15 degrees Fahrenheit. The pilot had preheated the engine for 30 minutes prior to flight. Despite the preheat, the combination of the cold temperature and the high oil viscosity may have affected engine performance.