Hughes 369D accident near Oakdale, California, July 3, 1999
On July 3, 1999 at about 5:00 pm local time, a Hughes 369D (helicopter), registered N8661F, was substantially damaged in an accident near Oakdale, California. It was an other work-use flight under external-load helicopter rules (Part 133). No one was hurt; 3 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
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.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 3, 1999 · about 5:00 pm local time
- Place
- Oakdale, California · map
- Type
- Accident
- Injuries
- No one was hurt; 3 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Hughes 369D · all 369Ds on the register
- Registration
- N8661F · no longer on the register · serial 690522D
- Damage
- Substantial damage
- Flight
- Other work-use flight · external-load helicopter rules (Part 133)
The NTSB's narrative final · quoted from the NTSB record
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.
The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.
The factual record from the NTSB's investigation tables, in plain English
Pilot
- Certificate: commercial pilot
- Ratings: single-engine land; instrument: airplane; rotorcraft: helicopter
- Flight time: 15,000 hours in all; 11,000 in this make and model
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: left
The aircraft
- Airframe total time: 8,323 hours
- Last inspection: 100-hour inspection, March 4, 1999; 75 hours since
- Maximum gross weight: 3,550 lb
- Seats: 3
- Landing gear: fixed
- Engine: Allison 250-C20B (turboshaft); 0 hours total
The flight
- Departed from: Oakdale CA at 4:00 pm
- Flight plan: none
- Runway 0
Weather at the time
- Light: daylight
- Visibility: 10 statute miles
- Sky: not recorded; clear
- Temperature: 72°F (22°C), dew point 43°F (6°C)
- Altimeter: 29.00 inHg
- Observation at 3:53 pm from MOD, 12 miles away
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 2 |
Documents from the investigation the NTSB's docket: the evidence folder behind the report
The docket, the folder of records gathered during an investigation (maintenance records, photographs, witness statements, examinations), has not been read from the NTSB for this case yet; the list appears here once it has. Open the docket at the NTSB.
Everything on this page comes from the NTSB's public records. The narrative, probable cause and findings are the NTSB's own words; the coded tables behind the report are written out in plain English, with pilots' ages, home towns and medical details left out. The documents and photographs are the NTSB's docket, shown as the NTSB released them. This site's own text never names anyone involved. A preliminary report can change; the final report usually follows one to two years later, and the page is refreshed when it does.