ASN Wikibase Occurrence # 201874
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| Date: | Saturday 25 November 2017 |
| Time: | 14:55 |
| Type: |  Cessna 172N Skyhawk |
| Owner/operator: | Private |
| Registration: | N739KW |
| MSN: | 17270613 |
| Year of manufacture: | 1978 |
| Total airframe hrs: | 1944 hours |
| Engine model: | Lycoming Engines O-320-H2AD |
| Fatalities: | Fatalities: 0 / Occupants: 3 |
| Aircraft damage: | Substantial |
| Category: | Accident |
| Location: | Lamar County between Purvis and Oloh, MS -
 United States of America
|
| Phase: | Landing |
| Nature: | Private |
| Departure airport: | McComb-Pike County Airport, MS (MCB/KMCB) |
| Hattiesburg-Bobby L. Chain Municipal Airport, MS (HBG/KHBG) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The pilot reported that, while the airplane was about 3,500 ft above mean sea level, the engine produced a "very rapid metallic banging/clanging noise," along with an instant loss of engine rpm. The engine was creating a "violent shaking" of the entire airframe. After about 20 seconds of applying carburetor heat, the pilot applied full mixture and started adjusting the throttle to obtain more power. He reported that, with more power applied, the shaking became more violent, along with a loss of engine rpm. The pilot realized that the engine power at this point was not sufficient to hold altitude. During a forced landing to a field, both wings and the fuselage sustained substantial damage.
Examination of the airframe and propeller found no preimpact mechanical malfunctions or failures that would have precluded normal operation. Examination of the engine revealed the No. 3 piston area displayed internal impact marks from the piston impacting the exhaust valve. The No. 3 exhaust valve was open and displayed impact marks from contact with the piston. The No. 3 valve spring seat (upper exhaust) was impact damaged with fractured pieces of the valve key (exhaust) and the valve stem cap (exhaust) laying on the bottom of the rocker area of the cylinder head. The No. 3 exhaust valve assembly moved freely inside the valve seats and was contacting the top of the piston.
Based on the available evidence, the partial loss of engine power was likely due to the No. 3 valve key (exhaust) failing, which resulted in a substantial reduction in engine power output. The reason for the failure was undetermined, as the service history of the valve key was unknown.
Probable Cause: A partial loss of engine power due to the failure of the No. 3 valve key (exhaust).
Accident investigation:
 |
|
Sources:
NTSB
FAA register: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?NNumbertxt=739KW
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 26-Nov-2017 03:06 | Geno | Added |
| 28-Nov-2017 07:27 | Anon. | Updated [Total occupants] |
| 09-Dec-2017 03:34 | Geno | Updated [Narrative] |
| 08-Jun-2020 08:39 | ASN Update Bot | Updated [Time, Operator, Nature, Departure airport, Destination airport, Source, Narrative, Accident report, ] |
| 08-Jun-2020 17:22 | harro | Updated [Departure airport, Destination airport, Source, Narrative, Accident report, ] |
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