Accident Sequence
On November 11, 2020, at 1144 Pacific standard time, a Cessna 177B airplane, N34633, was substantially damaged when it crashed near Whidbey Air Park (W10), Langley, Washington. The private pilot and flight instructor on board were fatally injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Earlier that day, the airplane flew from Boeing Field (BFI), Seattle, to Bellingham International Airport (BLI). At about 1110, it departed BLI southbound over Whidbey Island toward BFI, climbing to about 6,500 ft mean sea level. After about 16 minutes, groundspeed decreased and the airplane began descending. The flight instructor declared an emergency to air traffic control, reporting full power and RPM but about to lose the engine. He stated they could not maintain altitude despite full power and were descending. The controller advised toward W10, and the instructor reported intermittent power. The airplane crossed highway 525, then turned north toward W10. The instructor reported the airport in sight but later stated they were diverting off-airport. No further communication was received; the last radar point was over the runway at 300 ft.
A witness who had landed at W10 about 75 minutes earlier observed the airplane at pattern altitude moving west to east, then turning left to northwest. The propeller was not turning and no engine sounds were heard. As the airplane passed over the runway, the left wing dropped and it spun out of sight behind trees and hangars, followed by the sound of impact.
The engine monitoring system showed carburetor temperature decreasing from 31°F during the flight. At 17°F, there was an abrupt decrease in fuel flow and reduction in exhaust gas temperatures. Fuel flow spiked several times but immediately decreased.
Weather Conditions
The nearest weather station, 9 nautical miles southeast, reported at 1153: temperature 6°C, dewpoint 2°C. Plotting on the FAA carburetor ice chart, this temperature-dewpoint spread is consistent with serious icing at cruise power. The FAA Special Airworthiness Information Bulletin (CE-09-35) notes that carburetor icing can occur above freezing due to fuel vaporization and the Venturi effect, detected by RPM drop in fixed-pitch propeller airplanes.
Aircraft Examination
The airplane came to rest 153 ft west of the runway against 65-ft-tall trees, nose low at the base. Wings remained attached with aft crush damage; fuel tanks were breached. Cabin sustained extensive impact damage. Flight control continuity was established. Fuel system examination found minor debris in the strainer bowl but clear screen; fuel pump functioned normally; lines clear.
The engine showed no catastrophic failure. Induction and exhaust systems had crush damage. Thumb compression was obtained on all cylinders; magneto produced spark on all leads. Lower spark plugs exhibited severe worn-out signatures; cylinders normal. Carburetor had impact damage; inlet screen clear, throttle free, mixture arm separated. Internal floats and needle valve undamaged. Fuel pump and propeller governor normal. One propeller blade straight; second partially separated with striations.
The throttle cable fracture features were consistent with overstress fracture.
Medical Information
Autopsies of both pilot and flight instructor were performed. The flight instructor's cause of death was multiple traumatic injuries; toxicology positive for azacyclonol and fexofenadine, both FAA-approved for flight. The pilot's cause of death was multiple traumatic injuries; toxicology positive for Irbesartan, also FAA-approved.