Amateur-built Bucks Special N9065F accident near Prescott, Washington

Probable cause

Diminished engine performance due to carburetor icing conditions and multiple mechanical anomalies that did not allow for the airplane to attain adequate airspeed during takeoff from a planted field and failure to maintain clearance from obstructions. Contributing to the accident was improper maintenance.

NTSB analysis

The pilot of the tailwheel-equipped airplane reported that, during takeoff from a planted field and shortly after becoming airborne, the airplane was not able to climb. He then initiated a left turn to avoid trees and powerlines at the end of the strip. The left wing tip subsequently contacted the ground, resulting in a hard landing, noseover, and substantial damage to the wings and vertical stabilizer. The pilot reported a lack of performance that would not allow the airplane to gain altitude. It is likely that the airplane did not reach the normal takeoff speed due to the drag on the landing gear from the planted field and departed with insufficient airspeed for lift.

A postaccident examination of the engine revealed several anomalies. A portion of a fuel line was found looped around an engine mount, partially collapsing the line due to the sharp bend. This partially collapsed fuel line likely affected the fuel flow and operation of the fuel pump. A soft fuel pump line was attached to the impulse side of the fuel pump. The fuel line likely absorbed the pneumatic impulse from the crankcase, and it also may have affected the overall performance of the fuel pump. The air induction filter pleats were dirty, gray in color, and absent of the protective filter oil. A dirty air filter likely affected the fuel-air mixture to the cylinders. The carburetor venting tubes were modified with a tube that ran down the engine mount towards the bottom of the engine firewall. The venting tube was not placed in a neutral pressure zone, which likely affected the operation of the carburetors.

The beginning of the exhaust expansion chamber had a sharp 90° bend that would have likely restricted exhaust flow and the pressure pulse from the exhaust. The restriction in the exhaust combined with the other anomalies found during the postaccident examination would likely negatively affect the overall performance of the engine. The engine was test run and no anomalies were observed; however, the engine was not tested on a dynamometer or flown on an airplane. Therefore, whether the engine produced its rated horsepower was undetermined.

Review of the meteorological conditions that existed around the time of the accident and a carburetor icing chart indicated that conditions were conducive to the formation of carburetor icing at cruise power. The engine was not equipped with a carburetor heat system. Therefore, it is likely that carburetor ice accumulated, which resulted in a partial loss of power once airborne.

Text from the NTSB. Open the NTSB docket for WPR20LA122 for the full record.