Accident Details
On April 21, 2024, at approximately 1445 Alaska daylight time, a Cessna 120 airplane, registration N77032, sustained substantial damage during an accident at Talkeetna Airport (TKA) in Talkeetna, Alaska. The pilot, who was the sole occupant, was not injured. The flight was conducted as a personal flight under Title 14 Code of Federal Regulations Part 91.
Initial Events
The pilot reported performing a standard preflight inspection, including sumping fuel from both wing tanks and the gascolator. He verified that each wing fuel tank contained 6 gallons of fuel. After starting the engine, he allowed it to warm up for 10 minutes, observing normal operation. He obtained current weather information and taxied to the runway. Before takeoff, he conducted an engine run-up, checking both magnetos and carburetor heat with no abnormalities noted. The fuel selector was positioned to the right fuel tank, and the pilot departed.
Engine Power Loss and Forced Landing
The takeoff roll and lift-off were normal, and the pilot climbed using the airplane’s best angle of climb airspeed. When the airplane reached approximately 300 feet above ground level, the pilot observed the engine rpm fluctuate between 1,500 and 2,400 rpm about five or six 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 executed 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, causing the airplane to nose over. Substantial damage occurred to the wing lift struts.
Postaccident Examination
A postaccident examination of the airplane revealed that both wing fuel tanks were about half full. The gascolator, the fuel line from the gascolator to the carburetor, and the carburetor bowl were all full of fuel. Fuel samples collected from the right-wing fuel tank, gascolator, and carburetor bowl contained a very small amount of water. No obstructions were found in the fuel strainer in the gascolator or the inline fuel screen in the carburetor. The propeller was not available during the engine examination, but the owner’s mechanic stated that the propeller was undamaged with no signs of rotational damage.
The engine was examined postaccident. 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, with timing at 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; the right magneto connection had backed out about half a turn. With the P-lead grounds disconnected and the crankshaft rotated, only one spark plug lead (top left side) intermittently produced a weak spark. The magnetos were removed and bench-tested. All leads produced strong spark except for the No. 4 cylinder top spark plug lead and cylinder Nos. 2 and 4 bottom spark plug leads, which produced weak, difficult-to-see sparks. 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 turns. The high-tension spark plug wires had numerous spots of excessive wear. Resistance in the wires to the top spark plugs in cylinders No. 2 and No. 4 was high. When tested in a cable tester, the bottom leads to cylinders No. 2 and No. 4 failed. 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 and center electrodes, as did the top spark plugs to cylinders Nos. 1, 3, and 4. No obstructions were observed in the air intake or exhaust system.
Maintenance Records Review
Review of the maintenance records indicated that the last annual inspection was completed on August 7, 2023, with about 46 hours of tachometer time accrued between that inspection and the accident flight. Inspection of the ignition system and P-lead connections should have occurred during the last annual inspection. There was no logbook entry for the engine overhaul or reinstallation date. An undated entry indicated that the magnetos were installed about 567.11 hours since overhaul. One magneto had a yellow tag indicating an overhaul date of 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 environmental conditions were not conducive for the development of carburetor ice.