FTW94FA034

The student pilot made a forced landing after a total power loss shortly after takeoff. Engine examination revealed the cotter pin that fitted into the locking nut on the throttle lever was missing. The throttle lever serrated surfaces were not meshed and were riding on top of each other. The throttle valve was closed because the throttle opening spring, designed to fully open the throttle in case of throttle lever or cable separation, was broken. Three days before the accident, the throttle shaft was removed and inspected for wear. The mechanic said he was 'almost sure' he inserted the cotter pin when he reinstalled the carburetor. This was the first flight after the maintenance was performed.

History of flight

On November 15, 1993, approximately 1215 mountain standard time, a Cessna 172N, N4829E, was destroyed during a forced landing in a field near Fort Collins, Colorado, after the engine lost power. The pilot was seriously injured. Visual meteorological conditions prevailed, and no flight plan was filed for the instructional flight.

The following is based on interviews with the pilot and the Pilot/Operator Report. This was to be a student solo flight to the Fort Collins-Loveland Airport for touch-and-go landing practice. After takeoff, he made a right 30 degree crosswind noise abatement turn at an altitude between 800 and 1,000 feet above ground level (AGL), engine power decreased to idle. The pilot declared an emergency, attempted to troubleshoot the problem, then committed himself to a forced landing on a snow and ice-covered field. Braking action was nil and the airplane went down a hill and collided with an irrigation ditch.

Tests and research

During an examination of the airplane, the following was revealed: A cotter pin (p/n 82-14, ref. no. 51) that fits into the lock nut (p/n 81-311, ref. no. 49) on the throttle lever (p/n 12-B57, ref. no. 2) was missing. The serrated surfaces of the throttle lever were not meshed and were riding on top of each other. The throttle valve (p/n 14-190, ref. no. 4) was closed because the throttle opening spring (p/n 24-A10, ref. no. 24), designed to fully open (page number. 11-42) was broken.

The following entry was made in the airplane's Maintenance Discrepancy Log: "11/12/93 DISCREPANCY: Throttle shaft loose. REPAIRED OR DEFERRED: Removed carburetor and removed throttle

shaft from carburetor to inspect for wear. New throttle shaft and bushings on order. Reinstalled throttle shaft with proper torque and safety. Reinstalled carburetor on aircraft. Removal and installation done in accordance with Cessna Service Manual 11-42." Similar entries were made in the airframe and engine logbooks. At the time the work was performed, the airplane;'s total time in service and tachometer reading was 4148.5. At the accident site, the tachometer read 4148.5.

The airplane mechanic was asked if he recalled installing the cotter pin in the throttle lever lock nut. He answered, "I'm almost sure I did."