Cessna 172 N739KW

Summary

On 25 November 2017 at about 20:55 local time, a Cessna 172 registered N739KW was involved in an accident near Oloh, Mississippi, United States. 3 people were on board and one had minor injuries. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

25 November 2017 at 20:55

Classification

Accident

Location

Oloh, Mississippi, United States

Coordinates

31.2628, -89.5756

Aircraft

Cessna 172

Registration

N739KW

Category

Airplane

Year built

1978

Engines

1

Operator

Not recorded

Operating rule

Part 91: General Aviation

Purpose of flight

Personal

Phase of flight

Not recorded

Route

Mc Comb → Hattiesburg

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

ANC18LA011

1 person had minor injuries.

A partial loss of engine power due to the failure of the No. 3 valve key (exhaust).

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

Read the full NTSB narrative

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.

Quoted verbatim from the NTSB record.