ANC98LA099

The pilot had leveled off in cruise and was leaning the fuel mixture when the mixture control ceased to have effect. The pilot stated that the engine began to lose power, then quit. The airplane nosed over during the forced landing in tundra. Postaccident inspection revealed the mixture control cable had unscrewed from the mixture control arm. The cable had been replaced 238 hours prior to the accident, and was inspected 142, and 44 hours prior to the accident. The service manual specified the jam nut that locked the cable to the arm be torqued to 15 +/- 2 inch-pounds. There was no safety wire requirement for this linkage. If disconnected, gravity would allow the mixture control arm to fail to idle-cutoff.

On July 16, 1998, at 1725 Alaska daylight time, a Cessna 207 airplane, N1763U, sustained substantial damage when it nosed over during a forced landing 7 miles south of the King Salmon Airport, King Salmon, Alaska. The solo commercial pilot sustained minor injuries. The flight was operated under 14 CFR Part 135 by Yute Air Alaska, Inc., of Anchorage, Alaska, as a nonscheduled cargo flight. The flight departed King Salmon at 1720, transporting bypass mail to Egegik, Alaska. Visual meteorological conditions prevailed at the time of the accident, and a company VFR flight plan was filed.

The pilot told the NTSB investigator on July 16, 1998, that he leveled off to cruise at 700 feet msl, and began to lean the engine's mixture control. He said that about 10 miles south of King Salmon, the mixture control stopped having an effect on engine operation, and the engine began to lose power. While turning towards the airport, the engine lost total power, and he performed an emergency landing. During landing, the airplane nosed over.

Postaccident inspection revealed that the mixture control arm had unscrewed from the mixture control cable. The Cessna 207 Service Manual specifies the jam nuts which attach the cable to the control be torqued to 15 inch-pounds, plus or minus 2 inch-pounds. There is no safety wire required in the installation.

A review of the engine maintenance records indicated that the engine had received 100 hour inspections 44 hours, and 142 hours, prior to the accident. On both these occasions, Service Bulletin SEB95-15R1 (Throttle Control Lever Inspection) was performed. This lever is located next to the disconnected mixture control arm linkage. The mixture control cable was replaced 238 hours prior to the accident.

Inspection of a representative C-207 installation by the NTSB investigator-in-charge revealed that if the mixture control arm becomes disconnected, gravity allows the arm to fall to the lean / idle-cutoff position.