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On February 3, 2011, about 0945 Pacific standard time, an Aeronca 0-58C, N47503, collided with trees near San Luis Obispo, California. The pilot/owner was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot sustained minor injuries, and one passenger sustained fatal injuries; the airplane sustained substantial damage to the fuselage and wings. The cross-country personal flight departed Paso Robles, California, about 0920, with a planned destination of Oceano, California. Visual meteorological conditions prevailed, and no flight plan had been filed.
A Federal Aviation Administration (FAA) inspector interviewed the pilot, and provided the following information. The pilot stated that the airplane was in cruise flight at 3,500 feet mean sea level (msl). The engine started to cough and lose power. He attempted to restart the engine, and it ran for about 20 seconds. He then applied carburetor heat, but the cycle of losing power and restarting for a few seconds occurred several times. The pilot attempted to land in a field, but collided with trees at the edge of the field.
The pilot reported that he held a private pilot certificate with a rating for airplane single-engine land. He was issued a third-class medical certificate on July 19, 2010, with the limitation that he must wear corrective lenses.
The pilot reported that he had a total flight time of 315 hours. He logged 4.1 hours in the last 90 days, and 0.5 in the last 30 days. He stated that he had 20 hours in this make and model, and completed a biennial flight review on September 3, 2010.
The airplane was an Aeronca O-58C (L-3B), serial number 43-8212. The owner reported that the airplane had a total airframe time of 910 hours. It had an annual inspection on April 30, 2010.
The engine was a Continental Motors A-65-8, serial number 5292968.
The closest official weather observation station was San Luis Obispo, California (KSBP), which was 4 nautical miles (nm) southeast of the accident site. The elevation of the weather observation station was 212 feet msl.
An aviation routine weather report (METAR) for KSBP was issued at 0956 PST. It stated: wind calm; visibility 10 miles; sky clear; temperature 9/48 degrees Celsius/Fahrenheit; dew point 4/39 degrees Celsius/Fahrenheit; altimeter 30.48 inches of mercury; relative humidity 71 percent.
TESTS AND RESEARCH
Examination of the airframe and engine was conducted on February 8, 2011, at the facilities of Aircraft Recovery Services, Pearblossom, California. No evidence of preimpact mechanical malfunction was noted during the examination of the airframe and engine. Detailed examination notes are in the public docket.
The FAA Aircraft Certification Service published Special Airworthiness Information Bulletin (SAIB) CE-09-35 on June 30, 2009, to inform pilots of the potential hazards associated with carburetor icing.
The SAIB noted that carburetor icing doesn’t just occur in freezing conditions; it can occur at temperatures well above freezing temperatures when there is visible moisture or high humidity. It states that icing can occur in the carburetor at temperatures above freezing. Because vaporization of fuel, combined with the expansion of air as it flows through the carburetor (the venturi effect) causes sudden cooling, a significant amount of ice can build up within a fraction of a second. The SAIB contains a graph that illustrates the probability of carburetor icing for various temperature and relative humidity conditions.
The conditions for this accident fell within the range of serious icing at cruise power.
The FAA’s Handbook of Aeronautical Knowledge states that application of carburetor heat will cause a further reduction in power, and possibly engine roughness as melted ice goes through the engine. It states that these symptoms can last from 30 seconds to several minutes, depending on the severity of the icing.