HISTORY OF FLIGHT On May 17, 1993, at 1415 Alaska daylight time, a float equipped FH 1100 helicopter, N5060F, registered to Tom Walters, and operated by Sea Hawk, Inc., of Kodiak, Alaska, crashed into trees while attempting to execute a forced landing. The air taxi flight, operating under 14 CFR Part 135, departed Kodiak Municipal Airport on a company visual flight rules flight plan, and the destination was Malina Lake, near Malina Bay, on Afognak Island, Alaska. Visual meteorological conditions prevailed. The helicopter was substantially damaged and the Pilot-in-Command and the three passengers were seriously injured. According to the Pilot in Command, they had just made a low pass over an archeological site on the beach and were climbing over rising terrain and trees. The pilot heard a bang and immediately began to lose rotor RPM. He turned left to reach a small clearing and struck the tree tops at the edge of the clearing. The helicopter impacted the ground at the base of the trees. TEST AND RESEARCH The on site examination of the helicopter showed that the engine to transmission drive shaft assembly rotated freely in both directions. Subsequent metallurgical examination showed that the coupling on the engine end of the shaft failed as a result of fatigue cracking in the forward diaphragm. According to the Metallurgist, the location of fatigue initiation could not be determined due to the extensive post fracture rotational damage. Examination of the aircraft logbooks revealed the following information. The engine to transmission drive shaft, part number PN 19E49-3, serial number 2652 U, was installed on N5060F on June 1, 1990. Component time on this shaft was shown in the log book as Time since overhaul 962.9 hours. The logbook also shows that end pack assemblies, serial number 757AP and 711AP were installed and each had a total time 962.9 hours. Examination of the helicopter showed that the engine to transmission drive shaft that was actually installed was part number 19E49-3E, serial number 2717-U. The helicopter records contained a service record book which had this shaft's service record. The service record shows that shaft serial number 2717-U was removed in July 1978 with a total time of 140.0 hours. The next entry on the service record shows it was installed on helicopter serial number 242 in March, 1992 with a total time of 140 hours. The service record also shows that the end pack assemblies installed with this shaft were serial number 725 AP and 749 AP. The helicopter had 2669.9 hours total time when shaft number 2717-U was installed. The total time on the helicopter at the time of the accident was 2758.6 hours. The records further fail to show whether or not any of the following service bulletins or letters had been accomplished. Service Letter FH1100-24-5A Service Letter FH1100-24-6 Service Letter FH1100-24-7 Service Letter FH1100-24-9 Service Letter FH1100-24-10 Service Bulletin FH1100-24-7 Examination of the engine to transmission drive shaft (short shaft) shows that Service Letter FH1100-24-7 which outlined the procedures for installing vent plates, part number 2489839, was not accomplished. The reason for the Service Letter was to "vent the diaphragm packs to atmosphere to stabilize wear of the carbon sockets." Neither diaphragm pack had the vented plates installed. Service Letter FH1100-24-10 calls for an application of a Dow Corning coating to the diaphragms. Examination of the surfaces of the fractured diaphragm showed that a coating existed however, it could not be determined to be a Dow Corning coating. Examination of the short shaft center section revealed a variety of markings. One marking was an arrow indicating the direction of forward. The easily visible arrow indicated the correct direction. Beneath that arrow, another arrow, faintly visible under magnification shows the forward in the opposite direction. The metallurgical examination revealed other numbers peened over different numbers. The shaft had a Bendix data plate attached to the aft, center section of the shaft which showed the part number 19E49-3E and serial number 2717-U. A review of the Operator's "Operations Specifications," showed no requirement to comply with the Service Letters or the Service Bulletins. Examination of the lower isolation snubber mount of the transmission showed that the mount was worn and had become spongy. The mount is made of rubber and has square holes along its edges. The corners of these holes were starting to crack to lengths of 1/4 of an inch. According to Alaska Helicopters Maintenance, the isolation mount limits the movement of the transmission. When the mount becomes worn, the transmission may move in any direction more than normal and cause stress to be applied to the transmission to engine driveshaft. Alaska Helicopters has owned and operated FH100 helicopters under 14 CFR Part 135, however, they no longer operate any FH1100 helicopters. ADDITIONAL INFORMATION The Pilot-in-Command purchased the helicopter from Clearwater Helicopters in Florida. Clearwater Helicotpers was formerly Tampa Bay Helicopters.