Cirrus SR22 N969JB accident near Saginaw, Michigan

Probable cause

The failure of the right brake assembly due to excessive brake lining wear, which resulted in a thermally damaged piston O-ring, hydraulic fluid leak, and subsequent fire.

NTSB analysis

The pilot was taxiing from the fixed-base operator’s building to the runway. As he increased brake pressure to stop the airplane before the runway hold short line, it turned to the left and completed a full 360° turn before coming to rest. The passenger then offered to try his brake pedals but the airplane only turned to the left; the pilot and passenger concluded they had no control of the right brake. The passenger then observed a fire emanating from under the right wing. The airport’s aircraft rescue and firefighting personnel responded and extinguished a fire associated with the right brake assembly. The right wing’s lower surface sustained substantial thermal damage during the ground fire.

A postaccident examination revealed that the right brake linings had exceeded the manufacturer’s serviceable wear limit. The left brake linings were also significantly worn but within the serviceable wear limit. Additionally, the left brake assembly revealed a darkened temperature indicator sticker that indicated the left brake assembly had previously exceeded the manufacturer’s temperature limitation. The right brake assembly sustained significant thermal damage during the ground fire and its associated temperature indicator stickers were not observed.

The excessively worn brake linings would have resulted in increased brake temperatures being transferred to the brake pressure plate and pistons. The loss of right brake effectiveness and subsequent fire likely occurred when hydraulic fluid leaked past a thermally damaged O-ring installed on one of the right brake pistons, then caught fire when it contacted the hot brake assembly.

Text from the NTSB. Open the NTSB docket for CEN24LA014 for the full record.