Piper PA-18-150 N7154Z accident near Kenai, Alaska

Probable cause

The in-flight separation of a propeller tip due to an unauthorized and undocumented propeller repair.

NTSB analysis

The pilot, with one passenger aboard, departed in a float-equipped airplane from a remote lake. Shortly after takeoff, about 100 feet above the water, the airplane's engine began to vibrate violently. The pilot reduced engine power, turned the airplane left to avoid trees at the departure end of the lake, and attempted an emergency landing on the lake. The airplane continued to descend, and it subsequently collided with a shallow portion of the lake, sustaining substantial damage to the wings, fuselage, and empennage. A postaccident examination revealed that a 6-inch portion of one propeller blade separated, resulting in a severe imbalance.

An NTSB metallurgical examination of the fractured propeller blade revealed evidence of an unauthorized and undocumented repair of a nearly cylindrical hole, measuring about 0.3 inch in diameter. The examination also revealed areas where a white, opaque, plastic-like filler material, consistent with automotive body repair filler, was used to cover the hole before it was painted over, which subsequently made the unauthorized repair undetectable.

The airplane owner reported that the propeller was already installed when he recently purchased the airplane. In addition, no logbook entry was found that would have indicated any damage, repairs, modifications, or a propeller assembly installation.

Text from the NTSB. Open the NTSB docket for ANC12LA075 for the full record.