Accident Narrative
On August 25, 2021, at approximately 0945 Pacific daylight time, a Cessna 150D (registration N4375U) was substantially damaged when it collided with a fence during an off-airport landing near Ontario, California. The pilot sustained minor injuries. The flight was operated under Title 14 Code of Federal Regulations Part 91 as a personal flight.
The pilot reported that before departure, she added 16 gallons of fuel, bringing the total fuel aboard to 28 gallons. She maneuvered in the local area for about 2 hours 45 minutes before returning to the airport. During descent to 2,500 ft mean sea level (msl), the engine began to surge. In response, the pilot applied carburetor heat, and the engine sounded normal for 3 to 4 minutes before surging again.
As the airplane approached the airport, the pilot noted a partial loss of engine power, with the engine running between 1,000 and 1,200 rpm (near idle). She verified that the mixture was rich, the fuel selector was on "BOTH," and both magnetos were selected. Despite these attempts, the airplane could not maintain level altitude. The pilot selected an area for an off-airport landing. About 20 seconds before touchdown, the engine lost total power, and the airplane struck a fence, damaging the wings. After the accident, fuel was seen draining from the airplane, and moisture (haze) was visible.
Postaccident Examination
Postaccident examination at the site revealed the fuel tanks were intact, with only a small drip from the left fuel vent. The airplane owner recovered the aircraft and drained about 3.5 to 4 gallons of fuel from the left wing and about 0.5 gallons from the right wing. The carburetor bowl and gascolator both contained fuel.
A Cessna Aircraft representative stated the airplane was equipped with long-range fuel tanks holding a total of 38 gallons, with an estimated range of 800 miles (7.1 hours) at 5,000 ft msl, 2,500 rpm, and a cruise speed of 113 mph. The fuel system included an on/off fuel selector valve and interconnected fuel tanks. A check valve in the left fuel tank vent line contained a small (0.04-inch) hole designed to bleed pressure from a full tank. The representative noted that this hole could allow a small fuel drip when the airplane was in a left-wing-low position, with leakage depending on fuel head pressure and duration. Fuel could escape if damage occurred forward of the fuel valve. Based on the flight track, the representative estimated the airplane should have had more than 10 gallons of fuel at the time of engine failure.
Pilot's Comments
In a postaccident statement, the pilot indicated that, given the haze, she should have applied carburetor heat as soon as she began the descent. She also stated she should have had a greater fuel reserve and had planned for a 20% discrepancy in the airplane's fuel performance numbers.
Weather and Carburetor Icing Information
The meteorological aerodrome report for Chino, California, issued at 0953, reported a temperature of 79°F and a dew point of 61°F. These values, when applied to the FAA Carburetor Icing Probability Chart, fell within the "serious icing at glide power" portion of the chart.
The FAA published Special Airworthiness Information Bulletin (SAIB) CE-09-35 in June 2009, discussing carburetor ice prevention. The SAIB noted that carburetor icing can occur at temperatures well above freezing when visible moisture or high humidity is present, due to sudden cooling from fuel vaporization and the Venturi effect.