Bell 47D-1 accident near Riverside, California, July 6, 2001
On July 6, 2001, a Bell 47D-1 (helicopter), registered N64580, was substantially damaged in an accident near Riverside, California (Riverside Municipal airport). It was a personal flight under general aviation rules (Part 91). No one was hurt; 2 people were on board or involved. The weather was visual conditions (good weather).
The NTSB's probable cause their words, unchanged
The engine crankshaft's failure as the result of fatigue cracking initiated by surface damage and localized overheating due to the installation at overhaul of incorrectly sized bearings.
Source: NTSB aviation accident database, copy made October 5, 2026. Docket and reports at the NTSB.
What the record shows
- Date
- July 6, 2001
- Place
- Riverside, California · Riverside Municipal · map
- Type
- Accident
- Injuries
- No one was hurt; 2 people were on board or involved.
- Weather
- visual conditions (good weather)
- Aircraft
- Bell 47D-1 · all 47D-1s on the register
- Registration
- N64580 · no longer on the register · serial TWH-9
- Damage
- Substantial damage
- Flight
- Personal flight · general aviation rules (Part 91)
The NTSB's narrative final · quoted from the NTSB record
The helicopter experienced a rough running engine on short final approach and entered an autorotation, but made a hard landing and sustained substantial damage. The crankshaft failed as the result of fatigue cracking initiated by surface damage and localized overheating. The crankshaft was reportedly overhauled 165 hours prior to the failure. Optical examinations of the fracture faces found beach marks and crack arrest lines indicative of fatigue cracking though the majority of the crank cheek. Further examinations established that the fatigue initiated at two origins on the aft radius surface of the No. 3 main bearing journal about halfway between the journal and cheek surfaces. An oil stain covered the aft radius and cleaning revealed wide spread surface damage to the radius. The presence of an oil stain on top of the damage indicates that the damage occurred either during the overhaul or soon there after and was not a result of the failure. The damage extended from the journal surface up to the level of the origin area and completely around the journal. The surface damage consisted of circumferential scoring, intermittent tearing, and material flow. The radius also had a slight bronze hue. Further cleaning and inspections found similar damage and coloration on the forward radius of the No. 3 main bearing but no damage to other journal radii. The direct visual examination of the No. 3 main bearing journal surface showed heavy circumferential scoring and roughening but no visual indications of overheating. The majority of the other journals, both rod and main, also displayed similar scoring but to lesser degrees. Measurements established that the diameters of all main bearing journals were between 2.238 and 2.240 inches. All rod journals measured 1.927 inches in diameter. Conversations with a distributor for new Franklin engines indicated that standard bearing sizes for 6A-335 engines are 2.250 to 2.249 inches for mains and 1.9375 to 1.9365 inches for rods. Bearings for 0.010- and 0.020-inch undersize journals are available for both the main and rod journals. The measurements on the fractured crankshaft are consistent with 0.010 inch under size journals for both the mains and rods. The presence of a white layer along with the undersized journals does indicate that the crankshaft had been renitrided at some point in time. The Franklin 6V-335 was originally certificated in 1956. The type certificate is now held by iyPZL-RzeszowlÈ (PZL) of Poland.
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: rotorcraft: helicopter
- Flight time: 205 hours in all; 186 in this make and model; 9 in the last 90 days; 5 in the last 30 days; 155 as pilot in command
- Last flight review: May 21, 2001
- Medical certificate: Class 2 (valid medical--w/ waivers/lim.)
- Seat: left
- Injury: no injuries
Crew member
- Certificate: commercial pilot
- Ratings: rotorcraft: helicopter
- Medical certificate: Class 2 (valid medical--no waivers/lim.)
- Seat: rgt
- Injury: no injuries
The aircraft
- Airframe total time: 5,283 hours
- Last inspection: annual inspection, June 13, 2001; 67 hours since
- Maximum gross weight: 2,350 lb
- Seats: 2
- Landing gear: fixed
- Engine: Franklin 6V335 (piston); 0 hours total
The flight
- Departed from: CNO Chino CA at 11:30 pm
- Destination: RAL Riverside CA
- Flight plan: none
- Runway 16, 2,851 ft by 48 ft
- A second pilot was aboard
Weather at the time
- Light: daylight
- Wind: at 3 knots
- Visibility: 8 statute miles
- Sky: broken clouds at 20,000 ft; clear
- Temperature: 91°F (33°C), dew point 64°F (18°C)
- Altimeter: 29.85 inHg
- Observation at 11:53 pm from RAL
Injuries
| Fatal | Serious | Minor | None | |
|---|---|---|---|---|
| Crew | 1 | |||
| Passengers | 1 |
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.
Other NTSB records under N64580 the same tail number, which may have belonged to a different aircraft at the time
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.