Event ANC24LA025

Factual narrative

On April 21, 2024, about 1445 Alaska daylight time, a Cessna 120 airplane, N77032, sustained substantial damage when it was involved in an accident at the Talkeetna Airport (TKA), Talkeetna, Alaska. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported he performed his standard preflight inspection, which included sumping fuel from both wing tanks and the gascolator. He verified that each wing fuel tank contained 6 gallons of fuel. He started the engine and allowed the engine to warm up for 10 minutes and the engine operated normally. He obtained the current weather and taxied to the runway. Before takeoff he performed an engine run-up, which included checking both magnetos and carburetor heat with no abnormalities noted. He verified the fuel selector was in the right fuel tank position and departed. The takeoff roll and lift off were normal and he climbed using the the airplane’s best angle of climb airspeed. When the airplane reached about 300 ft above the ground, the pilot observed the engine rpm fluctuate between 1,500 rpm and 2,400 rpm about 5 or 6 times. He turned the airplane back toward 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 traveled about 40 yards before the landing gear dug into the snow and the airplane nosed over. The airplane sustained substantial damage to the wing lift struts. A postaccident examination of the airplane revealed both wing fuel tanks were about half full. The gascolator was full of fuel, the fuel line from the gascolator to the carburetor contained fuel, and the carburetor bowl was full of fuel. Fuel was collected from both wing tanks, the gascolator, and the carburetor bowl. A very small amount of water was observed in the fuel collected from the right-wing fuel tank, gascolator, and carburetor bowl. No obstructions were observed in the fuel strainer in the gascolator or the inline fuel screen in the carburetor. The propeller was not available during the engine examination. The owner’s mechanic stated that the propeller was undamaged with no signs of rotational damage. A postaccident examination of the engine was performed. The throttle, mixture, and carburetor heat controls were checked for continuity with no discrepancies noted. The engine crankshaft was rotated at the propeller flange and all valves moved smoothly and equally. Thumb compression was achieved on all cylinders. The magneto impulse coupler produced audible clicks when rotated. Both magnetos were securely fastened, and timing was about 30° before top dead center. The P-lead connection into the back of the left magneto was loose and had backed out about four full turns and the right magneto connection had backed out about a half a turn. The P-lead grounds were disconnected from both magnetos and when the crankshaft was rotated, only one spark plug lead on the top left side would intermittently produce a weak spark. The magnetos were removed and benched tested. All leads produced strong spark except for the No. 4 cylinder top spark plug lead and the cylinder Nos. 2 and 4 bottom spark plug leads, which produced spark that was weak and difficult to see. All spark plugs were securely attached except for the lower spark plug in the No. 4 cylinder, which was very loose and had backed out several full turns. The high-tension spark plug wires had numerous spots of excessive wear. Resistance in the wires going to the top sparkplugs in the No. 2 and No. 4 cylinders was high. The high-tension spark plug wires were tested in a cable tester; the bottom leads to cylinder Nos. 2 and 4 failed. The spark plugs were removed and compared to a Champion Check-a-Plug chart (AV-27): the spark plugs were in worn-out to normal condition. Electrodes showed normal erosion and the ground electrodes were about half of their original thickness. The bottom spark plugs to cylinders Nos. 1 and 4 had excessive gaps between the ground electrode and the center electrode, and the top spark plugs to cylinders Nos. 1, 3, and 4 had excessive gaps between the ground electrode and the center electrode. No obstructions were observed in the air intake or exhaust system. Review of the maintenance records revealed the last annual inspection was completed on August 7, 2023; about 46 hours of tachometer time accrued between the annual inspection and the accident flight. Inspection of the ignition system and P lead connections should have occurred during the last annual inspection. The was no logbook entry for the engine overhaul or reinstallation date. An undated entry indicated the magnetos were installed about 567.11 hours since overhaul. One magneto had a yellow tag indicating the overhaul date as June 26, 1992. The other yellow tag provided was for a different magneto than that installed on the engine. According to the carburetor icing probability chart, the environment conditions were not conducive for the development of carburetor ice. 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. Source: NTSB Aviation Accident Database Retrieved: 2026-02-12

NTSB Findings

Hierarchical cause / factor breakdown from the FAA bulk avdata database. Each finding tagged C (Cause) or F (Factor).

• — Aircraft-Aircraft power plant-Engine (reciprocating)-Recip eng wiring-Fatigue/wear/corrosion
• — Aircraft-Aircraft power plant-Ignition system-Spark plugs/igniters-Fatigue/wear/corrosion
• — Aircraft-Aircraft power plant-Ignition system-Dist (ignition harness)-Fatigue/wear/corrosion
• — Personnel issues-Task performance-Maintenance-Scheduled/routine maintenance-Maintenance personnel
• — Aircraft-Aircraft power plant-Ignition system-Ignition system wiring-Inadequate inspection