Accident Overview
On October 22, 2008, at about 2205 Pacific daylight time, a Stinson 108-1, registration N97946, suffered a partial loss of engine power shortly after takeoff. The pilot attempted a forced landing, but the airplane struck trees and came to rest inverted about 5.2 miles west-southwest of Concrete Municipal Airport in Concrete, Washington. The aircraft sustained substantial damage. The pilot, who owned and operated the airplane, was killed; the two passengers received serious injuries. Visual meteorological conditions prevailed during the dark nighttime flight. The personal flight was conducted under 14 CFR Part 91 without a flight plan and had originated from Concrete minutes earlier.
Flight History
According to a family member, the pilot was likely heading to Auburn, Washington, where the airplane was based. Earlier that day, the pilot and passengers had flown to Concrete to purchase an airplane for restoration. A front-seat passenger reported that seconds before impact, the pilot stated, "We are losing power." The passenger also noted no engine backfire or rpm surge during the flight.
Wreckage and Impact
The airplane came to rest within 75 feet of an occupied private residence. Residents reported seeing colored lights from the airplane at near tree-top altitude and described the engine noise as "on and off" and "sputtering or clanking." The aircraft impacted at least three trees about 50 feet above ground level before coming to rest upside down. Fuel was observed at the scene, but there was no fire.
Pilot and Aircraft Information
The 71-year-old pilot was a retired airline captain with experience flying numerous aircraft, including Boeing 747s. According to his last FAA medical certificate application (December 17, 2007), he had logged 34,100 total flight hours. He also held an FAA airframe and powerplant mechanic certificate and performed maintenance on the accident airplane. The Stinson 108-1 was manufactured in 1946 and equipped with a Franklin engine. Engine logbook records indicated the pilot performed inspections between 2001 and 2008. The tachometer reading on the day of the accident was 112.6 hours, up from 0 hours in 2001.
Medical and Toxicological Findings
An autopsy by the Skagit County Coroner's Office attributed the pilot's death to blunt force trauma from the crash. Forensic toxicology tests detected no ethanol, cyanide, or carbon monoxide. The following drugs were found: diphenhydramine (in blood and urine), ibuprofen (in urine), norpropoxyphene (in blood and urine), pioglitazone (in blood and urine), and propoxyphene (in urine only). Clinical findings included glucose in urine (805 mg/dl), glucose in vitreous (41 mg/dl), and elevated hemoglobin A1c (7.7 percent). On his last medical application, the pilot reported using metformin, pioglitazone, and lisinopril, and indicated a history of kidney stone, diabetes, and hospitalization. He held a third-class medical certificate requiring yearly reexaminations.
Engine Examination
Post-accident examination of the engine revealed a foreign object in the carburetor. A rope-like material, about 13 inches long, was found protruding from the carburetor's air inlet and wrapped around the fuel discharge nozzle. The material had been glued to the carburetor's heater muff as a seal/chafe strip. Marks on the muffler and shroud indicated the rope had come loose before the power loss. An FAA inspector opined that the pilot likely applied carburetor heat after takeoff, causing the rope to dislodge and be ingested into the carburetor, restricting airflow and resulting in the loss of engine power. The flight control system was intact, the main fuel screen was clean, and the propeller showed no torsion deformation or chordwise scratches.
Aftermath
The accident investigation concluded without a formally stated probable cause, though the ingested rope material was identified as the likely precipitating factor for the engine failure.