On October 21, 2003, at 1623 eastern daylight time, N3419S, a Cessna 182G, was substantially damaged when it impacted Lake Rohunta in Athol, Massachusetts, after experiencing a total loss of engine power. The certificated private pilot received serious injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal flight which originated at the Turners Falls Airport (0B5), Montague, Massachusetts, at 1615. The pilot was interviewed and reported that he had no memory of the accident flight. However, he did recall that his intention was to practice instrument procedures in visual meteorological conditions, and he departed 0B5 and intended to return to 0B5. According to a Federal Aviation Administration inspector, one witnesses observed the airplane on a "modified right base" to runway 32 at the Orange Municipal Airport (ORE), Orange, Massachusetts, but did not observe the impact. All other witnesses interviewed did not observe the airplane in the traffic pattern; they only heard an impact with the lake. Examination of the airplane revealed engine oil on the firewall, fuselage, wings, and vertical stabilizer; and a reading on the oil dipstick indicated 7.5 quarts of oil. The left wing fuel tank contained a "sufficient amount of fuel for the flight," and the right wing fuel tank was breached. The fuel selector position was positioned between the "Left" and "Both" detents. The mixture, throttle, propeller, and carburetor heat cockpit controls were all in their full forward positions. Additionally, no rotational scoring was observed on the propeller, and branches observed in the surrounding area did not display any propeller cut marks. The engine was recovered and examined. During the examination, it was noted that the magneto idler gear support pin and gasket were dislodged from the two attachment studs. The lock washers and both nuts for the attachment studs were not located, and the threads on the studs were unremarkable. Upon removal of the right magneto, the idler gear was observed disengaged from the magneto drive gears. Engine crankshaft continuity was confirmed by manual rotation of the propeller. Examination of the airframe and engine logbooks revealed the last annual inspection was performed on December 19, 2002, and the airplane had accumulated about 77 hours since that date. The entry for the annual inspection in the engine logbook stated that both magnetos had been removed during the inspection. The left magneto was overhauled, and the right magneto was disassembled and cleaned. The entry further stated, "..reinstalled both magnetos, and timed to specs." Weather reported at ORE, at 1636, included winds from 250 degrees at 11 knots, gusting to 17 knots, visibility 10 miles with thunderstorms in the vicinity, a broken cloud layer at 5,500 feet, an overcast layer at 8,000 feet, temperature 66 degrees Fahrenheit, dew point 48 degrees Fahrenheit, and barometric pressure of 29.38 inches Hg.