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| Date: | Friday 4 May 2018 |
| Time: | 19:30 |
| Type: |  Beechcraft A36 Bonanza |
| Owner/operator: | Private |
| Registration: | N36LP |
| MSN: | E-894 |
| Year of manufacture: | 1976 |
| Total airframe hrs: | 7951 hours |
| Engine model: | Continental IO-520-BB |
| Fatalities: | Fatalities: 0 / Occupants: 1 |
| Other fatalities: | 0 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Lafayette County, southeast Shullsburg, WI -
 United States of America
|
| Phase: | Landing |
| Nature: | Private |
| Departure airport: | Okmulgee, OK (OKM) |
| Plainfield, WI (WN09) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The commercial pilot reported that he heard an unusual noise from the engine during cruise flight and shortly afterward, the engine experienced a total loss of power. The pilot performed a forced landing to an open field.
Visual examination of the engine revealed a hole in the crankcase. A teardown examination revealed fretting on the crankcase mating surfaces, shifting of the No. 2 main bearing within the journal support, thermal damage consistent with a loss of oil lubrication, and separation of the crankshaft. The observed fretting damage was consistent with relative movement of the crankcase halves during operation due to a lack of through-bolt torque. The main journal bearing damage, the separation of the crankshaft, and the crankcase damage were secondary and a result of the loss of lubrication.
An engine overhaul was completed in about 11 years 5 months before the accident; about 849 flight hours had accumulated since the overhaul. Two cylinders were replaced 6 years before the accident, and one cylinder was replaced during the most recent annual inspection about 9 months before the accident. It is likely that improper torque of the through-bolt nuts was applied during one of the cylinder replacement events, though it could not be determined which event.
Probable Cause: A catastrophic engine failure due to improper torque on the engine through-bolt nuts, which resulted in relative movement between the crankcase halves, damage to a main journal bearing, and a loss of oil lubrication.
Accident investigation:
 |
|
Sources:
NTSB
FAA register: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=36LP
https://flightaware.com/live/flight/N36LP
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 07-May-2018 13:52 | Geno | Added |
| 07-May-2018 13:54 | Geno | Updated [Date, ] |
| 01-Jun-2019 07:28 | ASN Update Bot | Updated [Aircraft type, Operator, Nature, Departure airport, Destination airport, Source, Damage, Narrative, Accident report, ] |
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