Cessna 150D N4375U accident near Chino, California

Probable cause

The pilot’s delayed use of carburetor heat, which resulted in a loss of engine power due to carburetor icing.

NTSB analysis

The pilot flew in the local area for about 2 hours 45 minutes and then began to return to the departure airport. While the airplane was descending to 2,500 ft mean sea level, the engine surged, prompting the pilot to use carburetor heat. After a brief period of normal engine operation, the engine surging resumed, resulting in a partial power loss as the airplane approached the airport. Despite the pilot’s attempts to troubleshoot the issue, the airplane was unable to maintain altitude. The pilot performed an off-airport landing, during which the airplane collided with a fence.

During the recovery of the airplane, about 3.5 to 4 gallons of fuel from the left wing and about 0.5 gallons of fuel from the right wing were drained, and both the carburetor bowl and gascolator contained fuel. The fuel tanks in the wing were intact, but fuel was dripping from the left fuel vent due to the angle at which the airplane came to rest (left wing down). Because fuel was dripping from the vent, the investigation could not determine if the airplane had a sufficient amount of fuel aboard at the time of the engine failure; the amount of fuel found in the tanks did not represent the amount of fuel aboard before impact.

The Federal Aviation Administration (FAA) Carburetor Icing Probability Chart revealed that the outside air temperature and dew point temperature were within the "serious icing at glide power" portion of the chart, and the pilot reported haze in the area. An FAA Special Airworthiness Information Bulletin emphasized the risk of carburetor icing, even in above-freezing conditions with visible moisture, due to fuel vaporization and air expansion. Thus, it is likely that carburetor icing during the accident flight resulted in the loss of engine power, which might have been mitigated if the pilot had applied carburetor heat earlier in the descent.

Text from the NTSB. Open the NTSB docket for WPR21LA329 for the full record.