On July 18, 1997, approximately 1809 Pacific daylight time, a Cessna 170, N4292V, was substantially damaged in a forced landing following a loss of engine power in cruising flight near Graham, Washington. The private pilot received minor injuries and two passengers were not injured. The 14 CFR 91 local personal flight had departed the Cougar Mountain private airstrip near Yelm, Washington. The departure airstrip is approximately 11 nautical miles from the accident site, and the aircraft had been airborne for approximately 9 minutes at the time of the loss of engine power. Visual meteorological conditions were reported at McChord Air Force Base (AFB), approximately 9 nautical miles northwest of the accident site, and no flight plan had been filed.

The aircraft, a 1948 model, is powered by a Continental C145 series engine. The pilot told FAA investigators that during cruise flight, the engine RPM dropped smoothly to 800 RPM without a throttle reduction and would not recover to a normal cruise RPM. The pilot reported that he switched fuel tanks, left the mixture at full rich, and tried carburetor heat in response to the RPM drop, but did not attempt to switch magnetos. When remedial actions proved ineffective at restoring normal RPM, the pilot performed a forced landing over power lines onto a field located on soft rising terrain. The aircraft, which has fixed tailwheel landing gear, landed hard, partially collapsing the landing gear, and dug into the soft terrain.

The pilot reported that the aircraft was last fueled at Pierce County Airport/Thun Field, Puyallup, Washington, following an annual inspection at the end of June 1997. The pilot reported to FAA investigators that the aircraft had been flown 2 to 3 hours since the annual consisting of: flight from Puyallup back to the aircraft's home base at the Cougar Mountain airstrip (a straight-line distance of 18 nautical miles); a 0.6 hour local personal flight; and the accident flight. The pilot did not furnish a written narrative of the event with his NTSB accident report, but did report on the form that there were 20 gallons of fuel on board at takeoff, and that his preflight actions included checking oil and performing a sump drain.

In written statements, the passengers reported that the engine lost power (or that engine RPM dropped) and the aircraft subsequently landed in a field, ripping off a landing gear in the landing.

At the accident site, FAA investigators found that the aircraft's left wing fuel tank was empty, but that the right wing tank was 1/2 to 1/3 full. The FAA investigator subsequently conducted follow-up examinations of the engine, fuel, and carburetor. He reported that in a follow-up examination, 11 to 12 gallons of fuel was removed from the right fuel tank, and that this fuel was contaminated with about 3 pints of water. The FAA investigator reported that he also found water in the carburetor during this examination.

The FAA investigator subsequently took the carburetor to Precision Airmotive Corporation of Everett, Washington, the carburetor manufacturer, for a function check. The FAA inspector reported that the carburetor passed this function check.

The temperature at McChord AFB was reported as 23 degrees C, with a dewpoint of 11 degrees C, in its 1757 surface observation.

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