On October 2, 2021, about 1646 Pacific daylight time, an amateur-built Zenith CH750 airplane, N99HX, was substantially damaged when it was involved in an accident near the Fairways Airport, Oregon City, Oregon. The pilot was not injured, and the passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that he departed about an hour before the accident. Following an uneventful local flight, he entered the airport traffic pattern on left downwind for runway 32. After the pilot turned onto final approach, the passenger told him she smelled something burning, and shortly after the pilot did as well. The pilot stated that, a few moments later, the sound of the engine changed for about 5 seconds, followed by a total loss of engine power. The pilot realized he was unable to make it to the airport and initiated an off-airport landing between two tall trees. During the landing sequence, the airplane impacted trees and terrain before it nosed over and came to rest inverted, which resulted in substantial damage to both wings. Following the accident, the pilot reported that the right fuel tank appeared to be empty, and that some fuel was leaking “slightly” from the left wing fuel tank.

The pilot reported that, after refueling the airplane's left wing with 4 gallons of automotive fuel before the flight, the left wing contained about 10 gallons of fuel and the right wing contained about 3 gallons of fuel. When asked about verifying the fuel levels, the pilot stated that he measured the right fuel tank using the electronic flight information system and did not “dip the tank.” He said that the left fuel tank was “right between 3 and 4 gallons” before he added fuel, and that the after he fueled the left wing, it was at “7 gallons dipped via a dip stick.” The pilot reiterated that it was “7” gallons when he finished refueling and that the fuel burn rate was about 4.3 gallons per hour. The pilot reported on the Pilot/Operator Aircraft Accident Report Form that the airplane had 10 to 11 gallons of fuel at the time of takeoff. Postaccident examination of the recovered airplane revealed the fuel valves between the header tank and the wings were in the “off” position, and the fuel valve from the header tank to the electronic fuel pump was in the “on” position. The header fuel tank was void of any fuel. About a teaspoon of fuel was removed from the mechanical fuel pump. The electric fuel pump was turned on, and the pump emitted a loud audible noise, consistent with operating with no liquid (cavitating). No fuel was observed within either carburetor float bowl. The engine was test run “for several seconds” uneventfully. No evidence of any preexisting mechanical malfunctions were observed with the recovered engine or airframe.

The airplane was equipped with 2 wing fuel tanks (left and right), which have a total capacity of 24 gallons of fuel, of which 22 gallons is usable. In addition to the fuel tanks, the airplane was equipped with a 1.6 gallon header tank.