History of Flight
On October 6, 2023, at approximately 0945 eastern daylight time, a Cirrus SR22 airplane, registration N969JB, was substantially damaged while taxiing at MBS International Airport (MBS) in Saginaw, Michigan. The airplane was operating under Title 14 Code of Federal Regulations Part 91 as a personal flight. The pilot and passenger were not injured.
The pilot reported that after taxiing from the fixed-base operator's building to runway 23 via taxiways C and C4, he held short at the approach end of runway 23. When he increased brake pressure to stop the airplane, it turned left and completed a full 360° rotation before coming to rest. The passenger then attempted to use his brake pedals, but the airplane again only turned left, leading both occupants to conclude that the right brake was inoperative. Shortly thereafter, the passenger observed a fire emanating from under the right wing. Airport aircraft rescue and firefighting personnel responded and extinguished the fire, which originated from the right brake assembly. The lower surface of the right wing sustained substantial thermal damage during the ground fire.
Aircraft Information
A review of the airframe maintenance logbook revealed that the last annual inspection was completed on May 16, 2023, at an airframe total time of 2,572.7 hours. The logbook entry for that inspection did not reference the condition of or any work completed on the brake system. However, the associated work order included a discrepancy stating, “Brake discs beyond allowable limits (replace parts),” but no corrective actions were taken because, when rechecked, the brake components were reportedly “within allowable limits.” The work order invoice indicated no labor charge for the brake system inspection, although the aircraft owner was charged for eight replacement brake linings.
Further review of the logbook showed that the brake linings had last been replaced on March 19, 2015, at an airframe total time of 1,893.7 hours. At the time of the accident, the linings had accumulated 807.8 hours since installation.
Examination Findings
An examination of the left brake assembly revealed a darkened temperature indicator sticker, indicating that 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 temperature indicator stickers were not observed.
As part of the investigation, an aviation mechanic measured the thickness of the brake linings. The measured thicknesses were:
- 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
Postaccident examination established that the brake components were consistent with the original brake design before the release of Cirrus Service Bulletin No. 2X-32-12. According to the Cirrus SR22 Maintenance Manual, the serviceable wear limit for brake linings not modified by that service bulletin is 0.1 inch.