Bad mag brings down Grumman

This September 2009 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

Aircraft: Grumman Yankee. Injuries: 2 Minor. Location: Creswell, Ore. Aircraft damage: Substantial.

What reportedly happened: The engine lost power just after takeoff. The pilot was able to climb to about 300 feet above ground level, but the plane would not climb any higher. The pilot then switched fuel tanks, tried the carburetor heat, and turned on the electric fuel pump, but none of those helped, and the airplane began to lose altitude.

He then tried switching to the right magneto alone, and then to the left magneto alone. While on the right magneto only, the engine appeared to “stumble badly” and appeared to be trying to kick back. The pilot then switched to the left magneto only, and the engine smoothed out, but there was insufficient power for him to maintain altitude, and the plane continued to descend.

At that point, because he was approaching some trees that he did not feel he would clear, the pilot made a forced landing in a rough open field. Although the touchdown was uneventful, during the landing roll he realized that he was heading toward a manufactured home, and he did not think he would be able to stop before hitting it. He pushed full forward on the control wheel and applied hard braking. The nose wheel dug into the rough terrain, and the airplane nosed over onto its back.

The post-accident inspection determined that the engine’s right magneto had malfunctioned due to the resistance of the secondary coil windings being out of serviceable limits.

Probable cause: A partial loss of engine power due to the malfunction of the engine’s right magneto.

For more information: NTSB.gov. NTSB Identification: WPR09LA446