Aeropro Cz A220 N151J accident near Mccarthy, Alaska

Probable cause

The pilot’s failure to maintain directional control during the takeoff roll, which resulted in a loss of control and impact with terrain. Contributing to the accident were engine power surges due to the bent carburetor throttle valve lever.

NTSB analysis

The private pilot reported that, during the takeoff roll in the experimental amateur-built light-sport airplane, the engine began surging. He was unable to compensate for the sudden increase in left turning tendency when the engine power increased, and subsequently experienced a loss of control. Video footage of the accident was consistent with the pilot's statement. Examination of the engine, which was equipped with a two-carburetor system, revealed that one carburetor throttle valve lever was bent inward and made contact with the carburetor chamber top. While manipulating the throttle control from inside the cockpit, the throttle valve lever was observed moving only slightly before contacting the carburetor chamber top, which restricted its movement. This resulted in the carburetor being at the idle position during the point of contact. The other carburetor was free of anomalies and operated as designed.

During an engine test run with an exemplar engine of the same make and model, the carburetor throttle valve lever was modified to duplicate that found on accident engine. The engine was run at various power settings before applying full power. At full engine power, the carburetor throttle valve lever stuck against the chamber top and the engine ran rough and would not accelerate to maximum rpm. The carburetor throttle valve lever was then manually pushed forward past the point of contact on the carburetor chamber top, resulting in a burst of engine power immediately followed by smooth engine operation at maximum rpm.

Text from the NTSB. Open the NTSB docket for ANC16LA047 for the full record.