On June 24, 2004, a Cessna 185F (registration N4585F) was involved in an aviation accident near Bozeman, MT. Investigators recorded the probable cause as: The failure of the brake disk attachment flange due to fatigue cracking originating from corrosion pitting, rendering the right wheel brake inoperative and leading to the ground loop. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During landing roll, the aircraft ground-looped left when the right main gear brake failed. Investigation revealed fatigue failure of the brake disk attachment flange, originating from corrosion pits.
Accident Overview
During the landing roll, the pilot applied heavy braking to turn off the runway at taxiway Echo. The aircraft suddenly and rapidly ground-looped to the left.
Post-Accident Inspection
An initial post-accident inspection revealed that the right main gear brake rotor assembly had torn loose from the wheel itself, rendering the right wheel brake totally inoperative.
Laboratory Analysis
The wheel hub and brake disk assembly were shipped to the NTSB Materials Laboratory. Examination determined that the brake disk attachment flange failed in fatigue in the bend around the attachment flange. The brake disk showed a substantial amount of general corrosion. Although the attachment flange met the minimum thickness requirements, most of its surface was covered by corrosion and corrosion pitting. The fatigue crack propagation that eventually led to the failure had originated in one of these corrosion pits.
Probable cause
The failure of the brake disk attachment flange due to fatigue cracking originating from corrosion pitting, rendering the right wheel brake inoperative and leading to the ground loop.