19980520016109A

(.19) On may 20, 1998, at 0500 hours hawaiian standard time, a mcdonnell-douglas 500N, N112HD, experienced an uncontained engine failure during cruise and made an emergency landing in rough terrain, 5 miles north of lanai city, Hawaii. The helicopter was subsequently destroyed in a postimpact fire. The helicopter, operated by windward aviation inc., under 14 CFR part 135, was chartered by the maui police department. The commercial rated helicopter pilot and three maui police department officers were not injured. Visual meteorological conditions existed for the flight and no flight plan was filed. The pilot reported that at approximately 500 to 600 feet above ground level (AGL) the engine chip light illuminated. Approximately 10 seconds later, the engine-out light flickered and then fully illuminated. The pilot stated that as he performed an autorotation he heard a loud "bang." According to an federal aviation administration inspector from the honolulu flight standards district office, large holes were found in the main rotor blades. The inspector also noted that the blades from the number three and four turbine wheels were missing. (.4)the engine chip light illuminated during cruise and about 10 seconds later the engine out light flickered and then fully illuminated. As the pilot was performing an autorotation he and his passengers heard a loud bang, the helicopter landed on uneven terrain, and subsequently rolled over onto its side. A postcrash fire consumed the helicopter. The third turbine wheel was not located. The fourth turbine wheel was found remote from the helicopter with missing airfoils. In the 5 months prior to the accident, the power turbine had been removed for inspection and repaired several times due to one instance of an N2 lockup and chipped drive splines, and several instances of engine chip light illuminations with high temperatures and turbine rub. In each case, the plugs were removed, inspected per the manufacturer's maintenance manuals, and the oil system flushed. The day before the accident the engine chip light illuminated and the operator found a pasty substance on the chip detector. The chip detector was inspected in accordance with the manufacturer's maintenance manuals and the helicopter was then returned to service. Postaccident disassembly of the engine revealed an oil starvation failure of the no. 5 bearing and a subsequent failure of the no. 3 bearing due to a transfer of the axial loads normally carried by the no. 5 bearing. After the loss of the no. 5 bearing, there was an uncontained overspeed failure ot the power turbine rotor to loss of power turbine gear train engagement. Metal debris was incased on the tip of one od the chip detectors. The oil delivery tube that supplies oil to the no. 5 bearing was not recovered and was assumed to have consumed in the postimpatch fire. (-23) while conducting a night FAR 135 flight, at 600 feet AGL, the pilot received an engine chip light with an engine out audible and initiated an autorotation. During the autorotation the helicopter experienced an uncontained engine failure of the number 3 and 5 turbine wheels. The helicopter landed, rolled onto its right side and was consumed by a post fire.