Incident Overview
A pilot departed for closed traffic while the outside air temperature was approximately 12 degrees Fahrenheit and the dew point was approximately -8 degrees Fahrenheit. During the approach, the pilot turned final about 0.5 mile from the runway, noting that he was a "little" higher than anticipated. He reduced throttle, and the airplane intercepted the glide path about 350 feet from the end of the runway.
Engine Response Issue
As the pilot added throttle to maintain his descent angle, engine power did not increase. He waited a couple of seconds and added more throttle, but still no increase. He then added a "substantial" amount of throttle and started to flare the airplane. The engine responded, but before the pilot could arrest the descent rate, the airplane touched down short of the runway.
Post-Accident Examination
Examination of the engine and carburetor revealed no preimpact failures or malfunctions.
Research Findings
Research has shown that when engine power is reduced to idle, the engine cools rapidly, and vaporization of fuel is less complete, which can slow engine response times or cause a complete loss of engine power. Sudden throttle movements can aggravate this situation, and the pilot should try to keep the engine warm during glides by frequently opening the throttle.