CEN22LA076

The pilot reported that the airplane’s engine lost power during cruise flight. He executed a forced landing to a field, and the airplane nosed over when the pilot applied braking to avoid trees and a deep ravine. The airplane sustained substantial damage to the rudder and vertical stabilizer. The pilot attributed the loss of engine power to engine oil loss during flight. However, postaccident testing and inspection of the engine revealed that 6 quarts of oil remained in the engine. A test run of the engine was performed with no anomalies noted that would have precluded normal operations. Although there was oil staining and streaking on the exterior of the airplane, indicating a possible oil leak, there was still sufficient oil within the engine, oil pressure was normal during the postaccident test run, and no leaks were detected during the test run, leading to the conclusion that the loss of engine power was not due to an oil system issue. The temperature and dew point near the accident location at the time of the accident were conducive for serious carburetor icing at glide power. Thus, given the available information for this accident investigation, the loss of engine power was likely the result of carburetor icing.

On December 9, 2021, about 1652 central daylight time, an Aviat Aircraft A-1A, N111XJ, was substantially damaged when it was involved in an accident near St. Jo, Texas. The pilot sustained minor injuries, and the passenger sustained serious injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. According to the pilot, while the airplane was in cruise flight at 2,500 ft above ground level, the engine lost total power. The pilot executed a forced landing to a field, and the airplane nosed over while the pilot applied braking to avoid trees and a deep ravine. The airplane sustained substantial damage to the rudder and vertical stabilizer. In a postaccident statement, the pilot asserted that the loss of engine power was due to an in-flight oil loss. Postaccident examination noted that the bottom of the fuselage was covered with oil. The engine was found to contain 6 quarts of oil when checked using a dip stick, and no metal was found in the oil. The gasolator contained fuel, and the engine could be rotated by hand. No major oil leaks were observed within the cowling. A fuel supply from a temporary fuel tank was plumbed to the carburetor using gravity feed. Examination found that the throttle plate would not fully open at a high rpm. The propeller of the airplane had broken during the accident sequence, and a surrogate propeller was installed for an engine test run. The engine started within two revolutions. Afterward, a magneto check and propeller cycle check were performed; the results were normal. A full throttle rpm check was also performed, and a static rpm of 2,510 was achieved. No anomalies were detected during the test run, and all pressures and temperatures were normal. No oil leaks were detected except for a small amount of oil exiting the exhaust at engine start, which cleared after the engine was running. The airplane maintenance records indicated that an annual inspection was completed on October 19, 2021. During that inspection, the engine oil was changed, and a subsequent leak check performed with no leaks detected. According to the carburetor icing probability chart contained in Federal Aviation Administration (FAA), Special Airworthiness Information Bulletin CE-09-35, titled “Carburetor Icing Prevention,” the recorded temperature and dew point near the accident site about the time of the accident (26°C and 12°C, respectively) were in the range for serious icing at glide power settings. According to a similar carburetor icing probability chart, distributed by the Civil Aviation Safety Authority of Australia, the temperature and dew point were in the range for moderate icing at cruise power settings and serious icing at descent power settings.