ASN Wikibase Occurrence # 385651
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| Date: | Thursday 5 July 2001 |
| Time: | 17:01 LT |
| Type: |  Bell 47D-1 |
| Owner/operator: | Michael Zemlock |
| Registration: | N64580 |
| MSN: | TWH-9 |
| Total airframe hrs: | 5283 hours |
| Engine model: | Franklin 6V335 |
| Fatalities: | Fatalities: 0 / Occupants: 2 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Riverside, CA -
 United States of America
|
| Phase: | Approach |
| Nature: | Private |
| Departure airport: | Chino Airport, CA (CNO/KCNO) |
| Riverside Municipal Airport, CA (RAL/KRAL) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
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-Rzeszowlà (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.
Accident investigation:
 |
|
Sources:
NTSB LAX01FA236
History of this aircraft
Other occurrences involving this aircraft
| 1 September 2003 | N64580 | Private | 0 | Chino, California | |
sub |
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 05-Apr-2024 06:25 | ASN Update Bot | Added |
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