N6NW

On July 7, 1999, approximately 1600 Pacific daylight time, a Williamson/Williamson RV-4 amateur-built airplane, N6NW, experienced a loss of engine power on departure from North Bend, Oregon, and was substantially damaged in an ensuing forced landing near Coos Bay, Oregon. The commercial pilot-in-command, who was the aircraft's builder, received serious injuries in the accident. Visual meteorological conditions prevailed and no flight plan had been filed for the 14 CFR 91 local personal flight.

The 75-year-old pilot, who reported he had been a pilot for 60 years with over 10,000 hours total pilot time (including combat experience in World War II as well as previous designation as an FAA designated pilot examiner) reported on his NTSB accident report that the accident flight was the aircraft's third flight after completing a condition inspection 6 days prior to the accident, with no problems noted with the aircraft on the previous two flights. The pilot further reported that prior to the condition inspection, the aircraft had been in long-term storage since January 1999. The pilot stated:

...the engine suddenly stopped. I was at an altitude of less than 1,000 feet. I was over a ridge of hills and about 600 feet above ground level. To each side of the ridge was wet lands, plus a bay. With no suitable place to land, I noted a gently winding road with no traffic. I managed to get off a Mayday while trying to restart the engine....At about 300 feet above the surface, and on the final to landing, a vehicle comes out of a farm house driveway, stops momentarily, and then enters the road I was going to land on. With the car's slow speed, and my final approach speed, it was evident I was going to hit the car from the rear. Rather than do that, I turned my airplane to go up the driveway. It was then that I struck some fence posts....

Following the accident, on September 9, 1999, an examination of the aircraft's Lycoming O-320-E2D engine was performed by FAA inspectors at the pilot/aircraft owner's private airstrip near North Bend. The FAA inspectors reported one finding of significance to the NTSB, blockage of the carburetor air inlet. The inspectors' engine teardown report stated:

Following the normal check for spark, continuity of engine components, and fuel source/contamination, I looked for potential blockages of the engine inlet air system. The lower cowl was removed to gain access to the carburetor inlet air ducting. I found the fiberglass duct packed with dirt and dug it out....After the dirt was removed, a soft blue ball (2.5") dropped out of the updraft carburetor. There was scotch tape wrapped around the ball with loose flags of tape where it had been attached to the air duct. A 1" piece of red plastic tape was found taped to the ball as a flag against leaving it in the inlet. The alternate air source was left uncovered by the ball until it broke loose and moved aft into the carburetor. This explains the normal takeoff power and sudden engine failure in flight.

The FAA inspector who prepared the engine teardown report indicated to the NTSB investigator-in-charge that the tape-wrapped ball found in the carburetor air inlet was identified by the pilot/aircraft owner as an improvised engine air inlet cover, which he had placed in the engine air inlet to prevent foreign objects from entering the engine air inlet during ground storage of the aircraft. The FAA inspectors reported finding no other evidence of pre-impact mechanical malfunctions in the engine.