# NTSB SEA99LA108: Williamson/Williamson RV-4, N6NW, Coos Bay, OR, July 7, 1999 - Type: NTSB accident investigation - Classification: Accident · Serious injuries · Limited investigation · Final report - Date: July 7, 1999, 16:00 local (23:00 UTC) - Place: Coos Bay, OR - Coordinates: 43.370056, -124.140213 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=43.3701&lon=-124.1402&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Serious injuries - Injuries: 1 serious - Status: Completed, report December 4, 2000 - Report: Approved by Office Director - NTSB case key (mKey): 46770 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=SEA99LA108 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/46770/pdf - Page: https://openairdocs.org/ntsb/SEA99LA108 ## Probable cause Inadequate aircraft preflight inspection (engine air inlet cover not removed) by the pilot, resulting in obstruction of the carburetor air inlet in flight and consequent inflight engine stoppage. Factors contributing to the accident included a vehicle entering the attempted forced landing surface, and fence posts in the forced landing area. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power(total) - nonmechanical, climb - to cruise - aircraft preflight - inadequate, pilot in command (cause) - misc eqpt/furnishings,engine inlet covers - not removed (cause) - induction air ducting - obstructed (cause) - Forced landing, emergency descent/landing - object - vehicle (contributing factor) - On ground/water collision with object, emergency landing - object - fence post (contributing factor) ## Analysis The pilot reported that after takeoff, at an altitude of approximately 600 feet above ground level (AGL), the engine suddenly stopped. Attempts to restart the engine were unsuccessful, and the pilot attempted a forced landing onto a road. As the aircraft approached the road at about 300 feet AGL, a car turned onto the road. It became apparent to the pilot that the aircraft would overtake and hit the car from the rear if he attempted to land on the road, and the pilot thus attempted to turn the airplane to go up a driveway off the road. The airplane subsequently struck fence posts during the forced landing. FAA inspectors who performed a post-accident examination of the aircraft's engine found a 2 1/2 inch diameter soft blue ball, wrapped in Scotch tape and with a flag of red plastic tape attached, lodged in the carburetor air inlet. The inspectors reported that the aircraft owner identified the ball as an improvised engine air inlet cover, which he had placed into the engine air inlet to prevent foreign objects from entering the inlet during ground storage of the aircraft. The FAA inspectors reported finding no other evidence of pre-impact engine mechanical malfunction. ## Factual narrative 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. ## Aircraft - Registration: [N6NW](https://openairdocs.org/deregistered/N6NW-2013-04-09), registration cancelled 2013-04-09, S/N 1, built 1986 (OpenAirDocs) - Reported make and model: Williamson/Williamson RV-4 - Registry model: [Williamson/Williamson RV-4](https://openairdocs.org/model/williamson-williamson-rv-4) (registry code 056139U) (OpenAirDocs) - Registry engine: [Lycoming 0-320 series](https://openairdocs.org/engine/lycoming-0-320-series) (registry code 41508, reciprocating) (OpenAirDocs) - Category: Airplane, amateur-built - Serial number: 1 - Airframe hours: 540 - Engines: Lycoming O-320-E2D 150 horsepower reciprocating - Damage: Substantial damage - Flight: Personal, Part 91 - Registered owner: Boyd D. Williamson - Airworthiness certificate: Special, Experimental (Special) - Last inspection: Annual, July 1, 1999, 2 hours before - Departed: OTH, NORTH BEND, OR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 75; flight instructor, commercial; airplane ratings: multi-engine land, single-engine land, single-engine sea; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; seat: front; flight hours: 10,000 total, 542 in this make and model ## Weather - Conditions: Visual (VMC), Day - Wind: 320° at 13 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 63 °F, dew point 48 °F - Altimeter: 30.00 inHg - Observed at: OTH ## 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 19990707008459A](https://openairdocs.org/incident/19990707008459A), Jul 7, 1999: Amtr RV4, North Bend, OR, Substantial damage. Acft lost power on take-off and crashed, other circumstances are unknown. (.19) on July 7, 1999, approximately 1600 pacific daylight time, a… 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.