What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
Hughes 369D helicopter experienced a partial loss of engine power while performing work at a construction site, went into auto-rotation, made a hard landing in a corn field, and the main rotor cut off the tail boom, other circumstances are unknown. (.4)the pilot experienced a partial loss of engine power while established in an out of ground effect hover at 150 feet AGL and landed hard in the resulting autorotation. Postcrash examination of the engine revealed that the turbine had experienced oil starvation due to a failure of the oil pump. The aft bearing (gear case cover) of the fcu/oil pump drive spur gear had disintegrated due to failure of the ribbon-type ball separator, which was found in the bottom of the gearbox in two pieces and deformed. The balls were ejected into the gear case and one was ingested by the oil pump, which caused internal jamming and the resultant shearing of the splined adapter which drives the oil pump. The ball separator was manufactured from an austenitic stainless steel, instead of aisi 1010 as specified by the manufacturer, and the material exceeded allowable hardness specifications. Allison ceb 1228, issued November 20, 1985, calls for bearings with the ribbon-type, pressed steel separator, to be replaced with bearings that incorporate a one-piece machined steel separator. Compliance was due at the next accessory gearbox repair when the gearbox was opened. The mechanic reported that he had replaced the number 2.5 bearing and the spur adapter gear shaft 265 hours and 4 months before the accident, which would have provided access to the gearbox to accomplish the bulletin. (-23)on 7/3/99, at approximately 1030AM PDT, N8661F, Hughes 369D, piloted by a commerical pilot lost partial power of the engine, autorotated, impact terrain soft turf cornfield. The main rotor blades cut off the tailboom. The FAR part 133 flight was conducted for powerline maintenance under VFR VMC. No injuries to the pilot or two passengers. Maintenance personnel found the engine oil pump spur bearing liner failed.
As the FAA filed it
HUGHES 369D HELICOPTER EXPERIENCED A PARTIAL LOSS OF ENGINE POWER WHILE PERFORMING WORK AT A CONSTRUCTION SITE, WENT INTO AUTO-ROTATION, MADE A HARD LANDING IN A CORN FIELD, AND THE MAIN ROTOR CUT OFF THE TAIL BOOM, OTHER CIRCUMSTANCES ARE UNKNOWN. (.4)THE PILOT EXPERIENCED A PARTIAL LOSS OF ENGINE POWER WHILE ESTABLISHED IN AN OUT OF GROUND EFFECT HOVER AT 150 FEET AGL AND LANDED HARD IN THE RESULTING AUTOROTATION. POSTCRASH EXAMINATION OF THE ENGINE REVEALED THAT THE TURBINE HAD EXPERIENCED OIL STARVATION DUE TO A FAILURE OF THE OIL PUMP. THE AFT BEARING (GEAR CASE COVER) OF THE FCU/OIL PUMP DRIVE SPUR GEAR HAD DISINTEGRATED DUE TO FAILURE OF THE RIBBON-TYPE BALL SEPARATOR, WHICH WAS FOUND IN THE BOTTOM OF THE GEARBOX IN TWO PIECES AND DEFORMED. THE BALLS WERE EJECTED INTO THE GEAR CASE AND ONE WAS INGESTED BY THE OIL PUMP, WHICH CAUSED INTERNAL JAMMING AND THE RESULTANT SHEARING OF THE SPLINED ADAPTER WHICH DRIVES THE OIL PUMP. THE BALL SEPARATOR WAS MANUFACTURED FROM AN AUSTENITIC STAINLESS STEEL, INSTEAD OF AISI 1010 AS SPECIFIED BY THE MANUFACTURER, AND THE MATERIAL EXCEEDED ALLOWABLE HARDNESS SPECIFICATIONS. ALLISON CEB 1228, ISSUED NOVEMBER 20, 1985, CALLS FOR BEARINGS WITH THE RIBBON-TYPE, PRESSED STEEL SEPARATOR, TO BE REPLACED WITH BEARINGS THAT INCORPORATE A ONE-PIECE MACHINED STEEL SEPARATOR. COMPLIANCE WAS DUE AT THE NEXT ACCESSORY GEARBOX REPAIR WHEN THE GEARBOX WAS OPENED. THE MECHANIC REPORTED THAT HE HAD REPLACED THE NUMBER 2.5 BEARING AND THE SPUR ADAPTER GEAR SHAFT 265 HOURS AND 4 MONTHS BEFORE THE ACCIDENT, WHICH WOULD HAVE PROVIDED ACCESS TO THE GEARBOX TO ACCOMPLISH THE BULLETIN. (-23)ON 7/3/99, AT APPROXIMATELY 1030AM PDT, N8661F, HUGHES 369D, PILOTED BY A COMMERICAL PILOT LOST PARTIAL POWER OF THE ENGINE, AUTOROTATED, IMPACT TERRAIN SOFT TURF CORNFIELD. THE MAIN ROTOR BLADES CUT OFF THE TAILBOOM. THE FAR PART 133 FLIGHT WAS CONDUCTED FOR POWERLINE MAINTENANCE UNDER VFR VMC. NO INJURIES TO THE PILOT OR TWO PASSENGERS. MAINTENANCE PERSONNEL FOUND THE ENGINE OIL PUMP SPUR BEARING LINER FAILED.
NTSB investigation
The NTSB’s investigation of this event, with its probable cause and findings. Matched to this report by N-number and date.