Accident Overview
On July 8, 2019, at 1600 central daylight time, a Knight-Wilcox Varieze experimental airplane, registration N112EZ, made a forced landing onto an interstate after a total loss of engine power. The accident occurred near Kaneville, Illinois. The pilot sustained minor injuries and the airplane sustained substantial damage. One vehicle was struck during the landing; its occupant was uninjured. The airplane was registered to and operated by the pilot under Title 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed at the accident site, and no visual flight rules flight plan was filed.
Flight History
The flight departed from Waukegan National Airport (UGN), Waukegan, Illinois, at 1537 and was en route to Aurora Municipal Airport (ARR), Aurora, Illinois. During descent toward the destination, the pilot contacted the ARR air traffic control (ATC) tower. The controller informed the pilot that the ARR airspace was operating under instrument flight rules (IFR) due to low visibility and haze. The pilot remained north of the ARR airspace and requested a special VFR clearance, which was denied due to an inbound IFR flight.
Loss of Engine Power
While holding outside ARR airspace with a reduced power setting of about 1,900 rpm and carburetor heat off, the pilot reduced the mixture control approximately one inch. The engine then experienced a total loss of power, and the propeller completely stopped rotating. At about 1,600 feet above ground level (agl), the pilot initiated a steep dive to increase airspeed and allow the propeller to rotate and the engine to restart. During the maneuver, he added carburetor heat, but the propeller remained stationary. He pulled out of the dive at about 300 ft agl and identified the interstate as the best landing area.
Forced Landing and Collision
After aligning with the westbound lane, the pilot glided over several cars and maneuvered for an opening between vehicles. During the landing, the right wing contacted a pickup truck in the far right lane. The airplane veered right, the landing gear collapsed, and the pilot lost directional control. The airplane rotated 360 degrees and came to rest in the grass median.
Weather and Carburetor Icing Conditions
Reported weather at the accident time included an outside air temperature of 83°F, dew point 52°F, and about 34% relative humidity. The carburetor icing probability chart in the airplane flight manual and the Federal Aviation Administration Special Airworthiness Information Bulletin No. CE-09-35 indicated the airplane was operating in conditions associated with a risk of carburetor ice accumulation at glide and cruise power settings.
Flight Data and Engine Testing
The pilot used the Foreflight application to record flight data. According to the data, during the steep dive the airplane reached about 189 mph. The Varieze flight manual specifies a propeller minimum wind-milling speed of 70 mph and a propeller restart speed in a steep dive of 150 mph. The responding FAA inspector recovered the airplane to a local hangar and conducted an engine functional test run, which was successful with no anomalies noted. The test was unable to determine why the propeller did not rotate during the dive.
Prior Carburetor Ice Incident
The pilot reported that two days before the accident, while in cruise flight, carburetor ice accumulated and the engine ran rough. After applying carburetor heat, the engine stumbled but returned to full power once the ice cleared.