On April 25, 2007, about 1400 eastern daylight time, a Piper PA-32-300, N679DM, was substantially damaged while taxiing at Richmond International Airport (RIC), Richmond, Virginia. The certificated private pilot/owner, the pilot-rated passenger, and another passenger were not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the intended flight to Savannah/Hilton Head International Airport (SAV), Savannah, Georgia. The personal flight was to be conducted under 14 Code of Federal Regulations Part 91. According to the pilot/owner, she flew the airplane from Danbury, Connecticut, earlier in the day, and stopped at Richmond to refuel. Upon departing the fixed base operator (FBO), the pilot-rated passenger, in the right seat, taxied the airplane to the hold short area for runway 20. There, the pilot/owner took control of the airplane, did not engage the parking brake, and commenced an engine run-up. The pilot-rated passenger then noted a "wisp" of smoke in the cockpit, and notified the pilot/owner. The pilot-rated passenger then requested tower clearance to taxi to the nearest FBO, and just as clearance was received, another pilot radioed to get out of the airplane because the right landing gear was on fire. The occupants immediately exited the airplane, and as they were running away, heard a tire explode. The pilot-rated passenger, a certificated flight instructor who was onboard at the pilot/owner's request, for her "first big trip," noted that as he was taxiing on taxiway Alpha, he felt "no abnormalities, no softness in the brakes, and no pull in the aircraft." On May 5, 2007, the airplane was examined by an investigator from Piper Aircraft Company, under the oversight of a Federal Aviation Administration (FAA) inspector. According to the Piper Aircraft Investigative Report, the underside of the right wing exhibited "extensive" fire damage. The skin was breeched inboard and aft of the main fuel tank; however, the fuel tank itself was not fire-damaged. Blistering was noted on top of the right wing above the right main landing gear. The right main tire was deflated and severely burned. The airplane had recently been purchased by the owner, "extensively" updated, and, as confirmed by the airplane's maintenance logbook, had an annual inspection performed on April 24, 2007. During the inspection, the right main wheel and tire assembly were removed and the brakes were disassembled. The airplane was fitted with heavy-duty Cleveland brakes, and as part of the installation, the Cleveland maintenance manual required a shim insulator to be installed. The shim was missing. The Piper Parts Manual for the airplane also required a main gear axel spacer to be installed inboard of the wheel assembly, which was also missing. The absence of the spacer would have allowed contact between the rotating wheel and the stationary brake assembly.