Aviat Aircraft INC A-1A accident near St. Jo, Texas, December 9, 2021

The NTSB's narrative final · quoted from the NTSB record

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.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.