# NTSB FTW97LA298: Piper J3C-65, N5985V, Castle Rock, CO, August 3, 1997 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 3, 1997, 10:30 local (16:30 UTC) - Place: Castle Rock, CO - Coordinates: 39.370109, -104.849502 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=39.3701&lon=-104.8495&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 2, 1998 - Report: Approved by Office Director - NTSB case key (mKey): 20305 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW97LA298 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/20305/pdf - Page: https://openairdocs.org/ntsb/FTW97LA298 ## 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. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(partial) - mech failure/malf, cruise - normal - engine assembly,valve,exhaust - jammed (cause) - Forced landing, descent - emergency - On ground/water encounter with terrain/water, landing - roll - terrain condition - rough/uneven - terrain condition - none suitable (contributing factor) ## Analysis 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. ## Factual narrative On August 3, 1997, approximately 1030 mountain daylight time, a Piper J3C-65, N5985V, was substantially damaged when it collided with terrain during a forced landing 4 miles south of Castle Rock, Colorado. The private pilot, the only occupant aboard, was not injured. Visual meteorological conditions prevailed, and no flight plan had been filed for the personal flight that was conducted under Title 14 CFR Part 91. The flight originated at Englewood, Colorado, approximately 1000. According to the pilot, he was in cruise flight at 7,500 feet msl (above mean sea level) when the engine rpm (revolutions per minute) dropped from 2,350 to 1,700. He said that at that altitude, a minimum of 2,150 rpm is required to maintain flight. He configured the airplane for best glide and landed in an open but uneven field. The main landing gear was sheared off and the fuselage buckled. Postaccident examination disclosed the no. 4 cylinder exhaust valve was stuck open. According to the Teledyne Continental Motors representative who examined the engine, it took "a large hammer to drive the valve out." The valve stem and guide were coated with "gummy black deposits." The pilot, who is an aeronautical engineer and holds an A&P (airframe and powerplant) mechanic's license, said the same situation occurred on July 22, 1995 (see FTW 95-L-A312). Engine examination following that accident revealed the no. 4 cylinder exhaust valve was similarly stuck open, and was attributed to excessive carbon deposits from high octane aviation gasoline usage in a low compression engine. ## Aircraft - Registration: [N5985V](https://openairdocs.org/aircraft/N5985V), registered now, S/N 13640, built 1945 (OpenAirDocs) - Reported make and model: Piper J3C-65 - Registry model: [Piper J3C-65](https://openairdocs.org/model/piper-j3c-65) (registry code 7100510) (OpenAirDocs) - Registry engine: [Continental A&C65 series](https://openairdocs.org/engine/continental-a-c65-series) (registry code 17003, reciprocating) (OpenAirDocs) - Category: Airplane - Serial number: 13-640 - Airframe hours: 4954 - Engines: Continental C-85-F12 85 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Donald L. Brehm - Airworthiness certificate: Standard, Normal - Last inspection: Annual, December 1, 1996, 44 hours before - Departed: APA, ENGLEWOOD, CO - Flight plan: Unknown ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 49; private; airplane ratings: single-engine land; medical: class 3, valid medical--w/ waivers/lim; seat: right; flight hours: 940 total, 554 in this make and model, 890 as pilot in command, 22 in the last 90 days, 7 in the last 30 days, 1 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Visibility: 50 statute miles - Lowest ceiling: none - Temperature: 77 °F, dew point 57 °F - Altimeter: 30.00 inHg - Observed at: APA, 16 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19970803020499A](https://openairdocs.org/incident/19970803020499A), Aug 3, 1997: Piper J3C65, Castle Rock, CO, Substantial damage. Aircraft lost power and made emergency landing in open field, landing gear sheared off, fuselage damaged. ## Other investigations on N5985V (1) From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. - [NTSB FTW95LA312](https://openairdocs.org/ntsb/FTW95LA312), Jul 22, 1995: Piper J3C (N5985V), Englewood, CO, substantial damage. Probable cause: A PARTIAL POWER LOSS DUE TO A STUCK NUMBER FOUR EXHAUST VALVE. A FACTOR WAS THE LACK OF SUITABLE TERRAIN FOR A FORCED LANDING. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.