On October 19, 1995, at 0547 eastern standard time (est), a Piper PA-31, N693MA, piloted by a commercial pilot was substantially damaged from a left engine fire in cruise flight. Visual meteorological conditions prevailed at the time of the accident. The personal 14 CFR Part 91 flight was operating on a IFR flight plan. The pilot and two passengers reported no injuries. The flight departed from Munice, Indiana, at 0530 edt. The pilot stated that he had just leveled off the aircraft at 4000 feet mean sea level. Shortly thereafter, the left engine area erupted in flames. Upon seeing the fire the pilot pulled the mixture control to idle cutoff, and shut off the fuel selector valve for the left engine. However, the fire continued in the engine area until landing. The pilot received a vector from Indianapolis Approach Control for the emergency descent/landing at Anderson, Indiana. A post flight examination by the Federal Aviation Administration revealed that the left engine's turbocharger oil line was not attached at the accessory case on the engine. In a telephone interview with the pilot he stated that during the preflight he checked the oil on both engines, but did not open the engine side inspection doors. The pilot stated he did not feather the left engine, because he needed the extra drag to execute the rapid descent. The windmilling prop would drive the engine's oil pump, causing the engine's oil to be expelled out the accessory case opening. A telephone interview was conducted with the director of maintenance (DOM) for the company that owned N693MA. He stated this was the aircraft's first flight after a 50 hour inspection. The DOM said that a different mechanic had worked on each engine. The inspection was accomplished in accordance with Piper service report #230764. N693MA was then run up and checked for oil leaks, with none found. The DOM stated that it was not normal practice to remove the oil line to the turbocharger during a 50 hour inspection.