Consolidated Aeronautics Inc. LAKE LA-4-200 N2989P accident near Twentynine Palms, California

Probable cause

A partial loss of engine power due to inadequate ignition from cracked spark plugs and a failed magneto.

NTSB analysis

The pilot had recently purchased the airplane and was transporting it to his home airport. During the cross-country flight, the pilot stopped to refuel the airplane. During departure, the airplane climbed to an altitude of about 200 ft above ground level, at which point the engine lost partial power and was unable to maintain altitude. The pilot elected to perform an emergency off-airport landing, and the airplane touched down on desert terrain. During the landing, the airplane collided with a sign and nosed over, coming to rest inverted.

The airplane had undergone a pre-buy and an annual inspection about 10 flight hours before the accident. The pilot stated that, on the day before the accident, he flight tested the airplane, during which time the manual turbocharger went into overboost for “a second” before he pulled the power back.

A postaccident examination revealed that several ceramic cores of the spark plugs were cracked. The combustion chambers were free from deposits, consistent with a preignition or detonation event. It is unknown if the overboost event that the pilot described resulted in this damage.

The magnetos, while still installed on the engine, did not produce a consistent spark, and their timing could not be determined. The magnetos were then removed from the engine. The right magneto was functionally tested and operated normally. The left magneto capacitor lead insulation had previously been cut, exposing the center conductor wire, consistent with improper assembly. The contact point tungsten faces were both corroded and exhibited an oxide crust on the external surfaces of the tungsten. A functional test, revealed the left magneto would not produce spark at different rpms. The left magneto was likely not operating during the accident takeoff, which, along with the cracked spark plugs, would have resulted in a partial loss of engine power.

Text from the NTSB. Open the NTSB docket for WPR21LA171 for the full record.