Amateur-built W8 Tailwind N56PK accident near Oshkosh, Wisconsin

Probable cause

The loss of engine power during initial climb for undetermined reasons.

NTSB analysis

The accident occurred during the initial flight testing of the experimental amateur-built airplane. The pilot reported that, during the initial climb, at an altitude of about 200 feet above the ground, the engine began to lose power. He notified the tower air traffic controller of his engine emergency and began a turn to remain clear of nearby buildings. The airplane encountered a ditch during the forced landing and the forward fuselage and firewall were substantially damaged.

The airframe had accumulated 4 hours since it was issued an airworthiness certificate and the engine had accumulated 5.7 hours since its last major overhaul. The pilot/builder replaced the carburetor, spark plugs, and a cylinder since the last engine overhaul. A postaccident examination of the engine revealed that both spark plugs for the No. 4 cylinder were loosely installed into the cylinder head. The upper spark plug for the No. 4 cylinder was not seated on its cylinder gasket. Several spark plugs were removed and exhibited features consistent with the engine operating at a rich carburetor mixture setting. Although a carburetor-icing probability chart indicated that there was a serious potential for carburetor ice accumulation while operating at a reduced engine power setting, the postaccident investigation could not determine if carburetor ice contributed to the loss of engine power.

The postaccident investigation was unable to determine the reason for the loss of engine power, which could have been a result of the incorrectly installed spark plugs on the No. 4 cylinder, an excessively rich carburetor mixture setting, an accumulation of carburetor ice before takeoff, or any combination of the aforementioned issues.

Text from the NTSB. Open the NTSB docket for CEN11LA429 for the full record.