CEN24LA014

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.

A review of the airframe maintenance logbook indicated that the last annual inspection of the airplane was completed on May 16, 2023, about 5 months before the accident, at an airframe total time of 2,572.7 hours. The airframe logbook entry for the last annual inspection did not refer to the condition of or any work completed on the airplane’s brake system. However, the work order associated with the last annual inspection included the discrepancy, “Brake discs beyond allowable limits (replace parts),” but there were no corrective actions taken because when rechecked the brake components were reportedly “within allowable limits.” Based on the work order invoice, there was no labor charge associated with the brake system inspection despite the aircraft owner being charged for 8 replacement brake linings. Further review of the airframe maintenance logbook revealed the last time the brake linings were replaced was on March 19, 2015, at an airframe total time of 1,893.7 hours. At the time of the accident, the brake linings had accumulated 807.8 hours since they were installed. On October 6, 2023, about 0945 eastern daylight time, a Cirrus SR22 airplane, N969JB, was substantially damaged while taxiing at the MBS International Airport (MBS), Saginaw, Michigan. The pilot and passenger were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he taxied from the fixed-base operator’s building to runway 23 via taxiway C to taxiway C4 and held short at the approach end of runway 23. As the pilot increased brake pressure to stop the airplane, 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. An examination of 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. As part of the investigation, an aviation mechanic measured the thickness of the airplane’s brake linings. The measured thickness of the brake linings was reported as follows: Left inner brake lining, 0.144 inch Left outer brake lining, 0.120 inch Right inner brake lining, 0.066 inch Right outer brake lining, 0.052 inch The postaccident examination of the airplane’s brake system established that the brake components were consistent with the original brake designbefore the release of Cirrus Service Bulletin No. 2X-32-12. According to the Cirrus SR22 Maintenance Manual, if not modified by Service Bulletin No. 2X-32-12, the serviceable wear limit for the brake linings was 0.1 inch.