Accident Piper J3C-65 N5985V, Sunday 3 August 1997

You can contribute by submitting additional or updated information.

Date:	Sunday 3 August 1997
Time:	10:30 LT
Type:	Piper J3C-65
Owner/operator:	Private
Registration:	N5985V
MSN:	13-640
Year of manufacture:	1945
Total airframe hrs:	4954 hours
Engine model:	Continental C-85-F12
Fatalities:	Fatalities: 0 / Occupants: 1
Other fatalities:	0
Aircraft damage:	Substantial
Category:	Accident
Location:	Castle Rock, CO - United States of America
Phase:	En route
Nature:	Private
Departure airport:	Englewood, CO (APA
Destination airport:
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
While in cruise flight, engine RPMs dropped from 2,350 to 1,700, and the airplane began to descend. The pilot made a forced landing in an open, uneven field. The landing gear was sheared off and the fuselage was buckled. Postaccident examination of the engine disclosed the no. 4 cylinder exhaust valve was jammed in the open position. The valve stem and guide were coated with 'gummy black deposits.' The pilot had a similar accident on July 22, 1995 (FTW 95-L-A312). In that accident, the jammed exhaust valve was attributed to excessive carbon deposits from high octane aviation gasoline usage in a low compression engine.

Probable Cause: A partial loss of engine power due to a cylinder exhaust valve jammed in the open position from excessive carbon deposits. A factor was the lack of suitable terrain on which to make a forced landing.

Accident investigation: