What happened
While performing the takeoff roll, the flightcrew of N425EX, an Embraer ERJ-145, heard a loud impact within the airframe. Simultaneously, the crew noted irregular performance indicators coming from the number three engine. In response to these indications, the captain initiated an aborted takeoff, bringing the Embraer ERJ-145 to a halt on the runway.
Once the aircraft had stopped, the fire warning system for the number three engine was triggered. The crew attempted to suppress the flames using the onboard fire extinguishing equipment, but the system failed to contain the fire. The fire eventually spread into the fuselage, where it ignited approximately 12,600 lbs of US Mail cargo.
Findings
An investigation into the engine components determined that the high pressure compressor disk in the number three engine had suffered a failure. This failure was caused by a fatigue crack that began at a site of corrosion. The resulting debris from the disk failure was powerful enough to puncture the engine nacelle and cut the primary fuel line. This breach allowed fuel to escape and ignite, leading to the fire that consumed the aircraft's cargo.