Boeing 767-322 N644UA incident near Chicago, Illinois

Probable cause

the brake fire after landing was caused by hydraulic fluid leaking on to hot brakes.

NTSB analysis

Flight 949 conducted a normal landing under maximum landing weight and the crew did not receive any warnings or cautions. There were no system anomalies found except for the damaged left-hand brake assembly. Examination of the left brake assembly found that it caught fire due to catalytic oxidation, most likely as a result of the carbon disk being exposed to deicing fluid. The catalytic oxidation allowed the pistons from the brake housing to punch through the softened pressure plate and contact the rotor resulting in piston displacement, possible piston bushing damage and hydraulic fluid leakage.

When the 2R slide was unpacked at the manufacturer to determine why it did not fully inflate during the evacuation, the aspirator was found unattached. This was likely removed when the slide was packed for shipping because the slide would not have even partially inflated if it was not installed during the evacuation. When the slide was laid out, the two missing portions of the aspirator spider arms were found within the slide. Analysis of the fracture surfaces on both spider arms found that each had preexisting cracks. These preexisting cracks were stress risers that reduced the strength of the arms. Since the fracture faces contained no evidence of fatigue, the two arms fractured during slide inflation sequence which caused the slide to not properly inflate during the evacuation. The preexisting cracks most likely occurred during the manufacturing process.

Text from the NTSB. Open the NTSB docket for DCA10IA082 for the full record.