On July 16, 1999, at 1800 eastern daylight time, a Cessna 411, N660EM, piloted by an airline transport rated pilot, sustained substantial damage from fire and explosions while the airplane was starting engines at Oakland/Troy Airport, Troy, Michigan. The pilot and passenger reported no injuries. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 flight was not on a flight plan. The personal flight to Fort Scott, Kansas was originating at the time of the accident. In a phone interview, the pilot stated that about 145 gallons of 100 low lead fuel was added to the airplane's fuel tanks by the fixed base operator at Troy. He said that he started the left engine first without any problems. He said that he started the right engine next. He said that he heard a loud backfire or explosion after the right engine started. He said that he heard a second loud backfire or explosion. He said that he saw an area, about a one-foot wide, expanded upward. The area was described to be in the middle, top of the right wing, and about three to five feet outboard of the exhaust. He stated that the passenger saw flames coming from the right wing. He said that he shut down both engines. He stated that within 5 to 10 seconds, he saw 2 observers on the ramp area that started to fight the wing fire with their extinguishers. He said that he and his passenger evacuated the airplane. One of the witnesses stated that he heard two explosions and saw that the flames initially came from the underside of the right wing's trailing edge. He described the initial flame as one and a half-foot wide, golden in color, and a surface type flame. He said that as the flames grew, the flames gave off black smoke. He said that he fought the fire with a 50-pound dry chemical type C extinguisher. The responding fire department chief said that a "couple hundred foot" column of black smoke could be seen coming from the wing fire. He stated that the response time was four to five minutes. He said that the twin Cessna was facing north and the wind was coming from the west. He stated that the west winds blew the flames away from the fuselage. He said that the right wing outboard of the engine nacelle was on the ground with some wiring and some melted structure still present between the nacelle and the wing. The tops of the wing and tip tank were melted. The chief said that flames were observed coming out from the melted areas and from the nacelle area. Inspectors at the scene were unable to determine the source of the fire. The airplane records were reviewed and the review did not reveal any anomalies.