ASN Wikibase Occurrence # 169255
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| Date: | Wednesday 11 September 2013 |
| Time: | 07:15 |
| Type: |  Bell 47G5 |
| Owner/operator: | Private |
| Registration: | N7836S |
| MSN: | 7860 |
| Year of manufacture: | 1967 |
| Total airframe hrs: | 16798 hours |
| Engine model: | Lycoming VO-435 SERIES |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Bell 47G5 helicopter, N7836S -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Agricultural |
| Departure airport: | King City, CA (KIC) |
| King City, CA (KIC) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot reported that he was flying low over a field when he heard a “loud bang.” He initiated a precautionary landing, during which, the helicopter started to spin. The pilot lowered the collective, and the helicopter subsequently landed hard on a road. Postaccident examination of the helicopter structure revealed that one of the center frame tubes, located just aft of the cabin, had separated due to a fracture. Examination of the fracture surface revealed that a fatigue fracture initiated in the tube at the root of a fillet weld associated with a reinforcing fillet welded axially along the tube. The fatigue crack propagated through the thickness of the tube and circumferentially around the tube from both sides of the weld root. Darker corrosion product found on the fracture face indicated that the preexisting fatigue crack had been exposed to atmospheric elements. The tube fracture occurred in single-sided bending consistent with in-flight airframe loads. The helicopter’s most recent 100-hour inspection occurred about 1 month before the accident. According to manufacturer’s guidance, the 100-hour inspection required, in part, an inspection of all structural tubing and fittings for cracks, cuts, bends, corrosion, distortion, and damage. If maintenance personnel had adequately inspected this area, they might have identified the degradation of the tube.
Probable Cause: The failure of the helicopter’s center frame tube due to a fatigue crack and corrosion originating from a welded surface. Contributing to the accident was maintenance personnel’s inadequate inspection of the helicopter during its most recent 100-hour inspection.
Accident investigation:
 |
|
Sources:
NTSB
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 28-Aug-2014 06:08 | Aerossurance | Added |
| 21-Dec-2016 19:28 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 29-Nov-2017 09:15 | ASN Update Bot | Updated [Operator, Other fatalities, Departure airport, Destination airport, Source, Narrative] |
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