Hughes 369D N8661F

Summary

On 3 July 1999 at about 17:00 local time, a Hughes 369D registered N8661F, operated by Capricorn Helicopters, was involved in an accident near Oakdale, California, United States. 3 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

3 July 1999 at 17:00

Classification

Accident

Location

Oakdale, California, United States

Coordinates

37.7993, -120.7408

Aircraft

Hughes 369D

Registration

N8661F

Category

Helicopter

Engines

1

Operator

Capricorn Helicopters

Operating rule

Part 133: Rotorcraft Ext. Load

Purpose of flight

Other Work Use

Phase of flight

Not recorded

Route

Oakdale → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX99LA245

Nobody was injured.

The disintegration and failure of the oil pump drive spur gear aft bearing, which resulted in failure of the oil pump and subsequent oil starvation to the engine's turbine module. A factor in the accident was the failure of company maintenance personnel to comply with the manufacturer's service bulletin regarding replacement of the bearing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.