Cessna 175B N8115T accident near Hurley, Mississippi

Probable cause

The mechanic's failure to identify and remove a plastic sheath covering a portion of the mixture control cable during an annual inspection, which prevented the proper securing of the mixture control cable and full travel of the control at the carburetor and subsequently led to the pilot's inability to properly control the mixture control lever at the carburetor and the resultant partial loss of engine power.

NTSB analysis

The commercial pilot was flying the airplane on a cross-country flight, which was the first flight after the completion of an annual inspection. The pilot reported that he noted no anomalies during the preflight inspection or engine run-up. After takeoff, the airplane proceeded toward the destination airport between 1,200 and 1,500 ft mean sea level. After levelling off, the pilot slowly leaned the fuel-to-air ratio. The pilot added that, subsequently, the engine rpm "abruptly" decreased from 2,900 to 1,200. The pilot promptly pushed the mixture control to full rich, but this did not restore power. He then twice advanced the throttle, which briefly increased the engine power before it reduced to idle power again. He informed an air traffic controller of the problem, and the controller then provided the pilot with radar vectors to a nearby airport. However, after realizing the airplane would be unable to reach the airport, the pilot chose to execute a forced landing in a field, during which the nose landing gear separated from the airplane.

Examination of the engine compartment revealed that the mixture control in the cockpit was in the "full rich" position but that the mixture control lever at the carburetor was at the "idle cutoff" position. Movement of the mixture control in the cockpit resulted in the cable flexing rather than completely moving the mixture control lever at the carburetor, which was due to a plastic sheath that was covering a portion of the mixture control cable; the sheath prevented the cable from being properly secured and also prevented the full movement of the mixture control lever at the carburetor. The plastic sheath was not a part specified in the airplane's parts catalog.

During engine test-runs, the engine operated satisfactorily when the mixture control lever at the carburetor was in the "full-rich" position. Given that no other issues were identified during the postaccident test-run, it is likely that the plastic sheath's preventing the proper securing of the mixture control cable and full travel of the control at the carburetor led to the pilot's inability to properly control the mixture control lever at the carburetor and the subsequent partial loss of engine power. Although the mechanic who performed the last inspection indicated that he checked the mixture control for full travel and noted no discrepancies with the mixture control cable, he failed to detect the plastic sheath covering a portion of the mixture control cable, which prevented adequate securing of the cable.

Text from the NTSB. Open the NTSB docket for ERA16LA145 for the full record.