ERA12LA575 · Cessna 182Q

According to the pilot, he performed preflight carburetor heat checks at the recently overhauled engine's run-up speed and at idle. He thought that the rpm drop was less than the drop before the engine was overhauled, yet he chose to make the flight. After takeoff, the pilot climbed the airplane to about 3,000 ft mean sea level, where he determined that the optional carburetor temperature gauge was inoperative. He subsequently applied carburetor heat in 5-minute intervals when he changed tanks, which he did twice at 20-minute intervals.

Noting precipitation in the area, the pilot decided to cut the flight short and return to the departure airport. He applied full carburetor heat before descending the airplane using the descent procedures checklist. About 9 nautical miles (nm) from the runway, with carburetor heat applied and the fuel tanks set to "both," he continued a slow descent with 10-degrees flaps. About 6 nm from the runway, the pilot felt a "power drop." The engine was still running, but the airplane was descending faster than anticipated. The pilot applied more throttle and felt a "slight boost," but the airplane continued to descend and subsequently impacted trees. During the descent, the pilot repeatedly checked the controls, "pulling them in and out to make sure they were not stuck," including the carburetor heat, throttle, prop pitch (fully in), and fuel mixture (full-rich).

No evidence of any preexisting mechanical anomalies that would have precluded normal operation was found. Although the pilot subsequently noted that he was concerned that a preexisting crimp in the scat tube leading from the heat manifold to the carburetor might have caused the engine to lose power, this scenario was unlikely due to the relative size of the crimp and the fact that the pilot did not note any engine anomalies when he applied carburetor heat during cruise flight with higher air flow requirements.

The temperature and dew point at the time of the accident were conducive to the accumulation of serious carburetor icing at glide power, and the make and model of airplane is known to be more susceptible than most airplanes to carburetor ice formation. In addition, although the pilot reported adding carburetor heat before initiating a long descent, he did not report adding engine power periodically to warm the engine during that descent; thus, it is likely that the carburetor heat manifold cooled to a point where the air being supplied to the carburetor was insufficiently heated to protect it from icing.

A review of Federal Aviation Administration, manufacturer, and advocacy group carburetor icing publications revealed disjointed and incomplete information. The lack of comprehensive, easily accessible carburetor icing information in a single location likely affects the overall pilot community's understanding of the subject and could have affected the pilot in particular.

Verbatim NTSB analysis and probable cause from the NTSB dataset