Cessna 120 N77032 accident near Talkeetna, Alaska

Probable cause

A degraded ignition system, which resulted in a total loss of engine power. Contributing to the accident was maintenance personnel’s inadequate inspection of the ignition system.

NTSB analysis

The pilot reported that the engine rpm began to fluctuate just after takeoff, so he turned back to the airport and verified the fuel selector position. During the turn the engine lost all power and the pilot made a forced landing into snow-covered terrain short of the runway. The airplane’s landing gear dug into the snow, and the airplane nosed over and came to rest inverted.

A postaccident examination of the airplane revealed the airplane contained about half a tank of fuel. Fuel was present throughout the fuel system; no obstructions were observed in the gascolator fuel strainer or the in-line fuel screen in the carburetor. The P-lead connections into both the left and right magnetos were loose. The crankshaft was rotated and only one spark plug lead produced a spark. The magnetos were placed on a test bench and all but three of the leads produced a strong spark.

The installed spark plugs were in worn-out condition. Five of the sparkplugs had excessive gaps between the ground electrode and the center electrode.

Inspection of the ignition system and P lead connections should have occurred during the last annual inspection. It is likely that the degraded, poorly maintained ignition system resulted in the total loss of engine power.

Text from the NTSB. Open the NTSB docket for ANC24LA025 for the full record.