On September 19, 1998, a Piper PA-20-180 (registration N6028D) was involved in an aviation accident near Thornton, CO. Investigators recorded the probable cause as: The propeller blade failed due to fatigue from corrosion pitting. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a banner tow flight, a propeller blade separated due to fatigue from corrosion pitting. The engine swung from its mounts, and the remaining blade penetrated the cockpit. The aircraft became uncontrollable and crashed into a field after striking trees.
Incident Overview
During a banner tow flight at an altitude of 1,200 feet above ground level, a portion of a propeller blade separated from the aircraft. The failed segment measured 21.6 inches from a two-bladed propeller with a total length of 38 inches per blade.
Sequence of Events
After the blade separation, the engine detached from three of its four mounting points and swung against the right side of the aircraft. The remaining propeller blade penetrated the cockpit structure but did not strike the pilot. The aircraft subsequently became uncontrollable and descended, impacting a field after striking trees in the backyard of a residence. The pilot sustained serious injuries.
Cause of Failure
The propeller blade failed due to fatigue cracking resulting from corrosion pitting. This metallurgical condition compromised the blade's structural integrity, leading to the in-flight separation.
Probable cause
The propeller blade failed due to fatigue from corrosion pitting.