LAX01FA236 · Bell 47D-1
Bell 47D-1 · Accident: loss of engine power on approach
From Chino Airport (CNO) to Riverside Municipal Airport (RAL)
Event
- NTSB case
- LAX01FA236
- Event typeAccident: someone killed or seriously injured, or the aircraft substantially damaged (NTSB definition). Incident: an occurrence that affected or could have affected safety, short of that. Glossary
- Accident
- InvestigationHow far the investigation had got when the record was published: preliminary, ongoing, final or completed. Unknown where the source does not say. Glossary
- Completed
- API-reported fatalities
- 0 · all aircraft and ground
- Ground fatalities
- Unknown
- OperationWhat kind of flying it was, grouped by the rules it flew under: airline (US Part 121), air taxi and commuter (Part 135), general aviation (Part 91 and similar), military or government. Glossary
- General aviation
- WeatherVisual meteorological conditions (VMC): good enough to fly by looking outside. Instrument conditions (IMC): cloud or low visibility, flying by instruments. Glossary
- Visual Meteorological Cond
Bell 47D-1
- Aircraft type
- Bell 47
- Category
- Helicopter
- RegistrationThe aircraft's tail number, such as N12345 or G-ABCD. Registrations are reissued, so the same one years apart can be a different aircraft. Glossary
- N64580
- Operator
- Unknown
- Onboard fatalities
- Unknown
- Route
- From Chino Airport (CNO), Chino, CATo Riverside Municipal Airport (RAL), Riverside, CA
- Aircraft age
- Not recorded
- Flight rulesThe regulations the flight operated under: in the US, Part 91 (general aviation), Part 121 (airlines), Part 135 (air taxi and commuter) and others; for flights abroad, the NTSB's coarser commercial or non-commercial code. Glossary
- Part 91: General Aviation
- Phase of flightThe stage of the flight when things started to go wrong: standing, taxi, takeoff, initial climb, en route, maneuvering, approach or landing. Glossary
- Approach · VFR pattern final
- First occurrenceThe single coded event the NTSB judges best describes what happened (records from 2008 on). Older records name the first occurrence in the sequence instead. Glossary
- Loss of engine power
- DamageDestroyed: beyond practical repair. Substantial: damage that affects the structure, performance or handling and normally needs major repair. Minor: less than that. Glossary
- Substantial
Cause areas
- Engine assembly, bearing › Oversize
- Engine assembly, crankshaft › Failure
- Engine assembly, crankshaft › Fatigue
- Engine assembly, crankshaft › Overtemperature
- Engine assembly, crankshaft › Previous damage
- Other maintenance personnel › Maintenance, overhaul, improper
Approximate · Coordinates from the NTSB case API, which marks them as estimated or does not say; no uncertainty radius is established.
NTSB narrative
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.
Probable cause
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.
Verbatim NTSB analysis and probable cause from the NTSB dataset
Sources
NTSB record LAX01FA236
- Event ID
- 20010713X01427
- Case number
- LAX01FA236
- Dataset
- historical-pre2008
- Source SHA-256
- 89e2df6d848e7ab3b42e7d7c7a03ff403303057a26ca04c95b3ea67201c3ce74
Source notes (4)
- Unreviewed is an editorial label, not an investigation status. API-sourced is not report-checked or human-reviewed. Explicit event totals are used without summing aircraft injury tables; onboard allocation is withheld. Unknown values remain unknown. The operation category is mapped from the NTSB-reported FAR part and has not been reviewed.
- Filled from the NTSB case API where the bulk record had no value: local date, investigation status, coordinates. Values present in the bulk record are kept.
- The date is the local date; the NTSB stores the UTC date 2001-07-06.
- API snapshot SHA-256: 153df4360650861beb4c6a5439bd5942b28ad0077e9008e463319114e0540ea5; retrieved 2026-09-22T11:47:40.979Z.