Bell 47D-1 N64580

Summary

On 6 July 2001 at about 00:01 local time, a Bell 47D-1 registered N64580 was involved in an accident near Riverside, California, United States. 2 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

6 July 2001 at 00:01

Classification

Accident

Location

Riverside, California, United States

Nearest airport

Riverside Municipal (RAL)

Coordinates

33.9500, -117.4500

Aircraft

Bell 47D-1

Registration

N64580

Category

Helicopter

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Chino → Riverside

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

LAX01FA236

Nobody was injured.

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.

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

Read the full 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-RzeszowlÈ (PZL) of Poland.

Quoted verbatim from the NTSB record.