On October 29, 1993, at 1240 eastern daylight time, a Bell 206L, N16696, owned and operated by Island Helicopters, Inc., of Garden City, New York, made a forced landing in the East River due to a power loss. There was no damage to the helicopter, and no injuries to the 2 pilots and 4 passengers. Visual meteorological conditions prevailed and no flight plan had been filed for the flight operating under 14 CFR Part 91. The helicopter was being operated on a local sighseeing revenue flight. It was cruising at 1400 feet. In the NTSB Accident Report, the pilot stated: ...At approximately 12:35 hours local we experienced an in flight engine shutdown. Ron was flying the aircraft and as soon as the failure occurred, I took the controls in a coordinated exchange. Ron had already started to initiate the autorotation. I armed the floats and issued a mayday call to LGA [La Guardia Control Tower]. Ron deployed the floats on my command and I completed the autorotation landing to water.... An engine tear down was conducted at Airwork, in Millville, New Jersey. It was observed by Mr. Mark Evans of Allison, Indianapolis, Indiana, and Mr. Bill Young, FAA, Farmingdale, New York. According to the engine records, it had been assembled by Island Helicopters. At the time of the power loss, the engine had accumulated 194.6 hours. According to a written report from Mr. Evans: Summary of Findings 1. The engine lost power due to loss of the splined joint at the turbine splined adapter and the aft end of the gas producer turbine to compressor coupling. The splines in this area were worn to the point of disengagement. 2. The splines in the area of distress appeared dry. 3. The "O" ring on the aft end of the spur adapter gearshaft was found cut and not in its proper position.... Additionally, Mr Evans said during the teardown, they found areas in the engine with carbon deposits that were consistent with a lack of lubrication. He also said the out of position "O" ring would cause a lack of lubrication to the splined adapter, and other areas of the engine. In a letter, Mr. Bill Young stated: ...There is an O-ring which is visually installed in the aft end of the compressor cavity. After which the installer should feel, with the tip of his finger, that the O-ring has seated properly...As the two halves of the engine are mated, the O-ring can no longer be seen. At this point, it could be rolled out of position or damaged. Should the above condition occur, a sufficient amount of oil to lubricate and cool the coupling might not be present to allow for proper operation of the coupling....