NTSB Identification: WPR11LA320
14 CFR Part 137: Agricultural
Accident occurred Saturday, July 09, 2011 in Yuba City, CA
Probable Cause Approval Date: 08/14/2014
Aircraft: SCHWEIZER AIRCRAFT CORP G-164B, registration: N7503L
Injuries: 1 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The pilot reported that, during the initial climb, he heard a “loud pop” and observed fire coming from both exhaust stacks before the engine lost power. He subsequently made an off-airport landing to an adjacent road. During the landing, the airplane slid into a ditch, the landing gear sheared off, and the airplane nosed over. A postaccident engine examination revealed that the blade retaining ring of the 1st-stage compressor blades had fractured into several pieces; about 30 percent of the ring was not recovered. A metallurgical examination of the recovered sections of the retaining ring revealed that all but two of the fractures were due to ductile overload. An examination of the nonoverload fractures revealed fatigue originating from the rivet hole areas, which was indicative of high-cycle fatigue. The power section had been overhauled 747 hours before the accident. According to the overhaul manual current at the time of the overhaul, the blade retaining ring was an on-condition inspection item and not required to be replaced at overhaul. The fatigue fracture of the 1st-stage compressor blade retaining ring likely affected the engine’s ability to produce power.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

High-cycle fatigue on the 1st-stage compressor blade retaining ring, which resulted in the ring’s fracture and a subsequent loss of engine power.

Full narrative available

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