On April 23, 2022, about 1820 Pacific daylight time, a Cessna 170B, N4398B, was substantially damaged when it was involved in an accident near Ravensdale, Washington. The pilot and passenger were seriously injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot reported that he departed Arlington Municipal Airport (KAWO), Arlington, Washington, about 0900 for a cross-country flight with multiple intermediate legs and a return destination to AWO (see Figure 1). Before departure, the pilot topped off the airplane fuel tanks with about 34-36 gallons of 100LL. After departing AWO, the pilot arrived at Whidbey Air Park (W10), Langley, Washington, which was about 14 nautical miles (nm) to the southwest and picked up a passenger. They then departed W10 about 1215 enroute to Ferry County Airport (R49), Republic, Washington, about 158 nm east. According to the passenger, they landed about 1350 without incident and stayed at the airport for about 3 hours. About 1700, they departed for a return flight back to W10. The passenger reported that, without his knowledge, the pilot changed course while enroute and diverted to Enumclaw Airport (WA77), Enumclaw, Washington, to pick up the pilot’s brother-in-law. About 1 hour and 20 minutes into the flight as the airplane passed Stampede Pass, Washington, about 3,000 ft above the ground, the engine lost all power. The pilot immediately verified that the mixture and throttle control settings were advanced and switched the fuel selector lever from BOTH to the right tank and then to the left tank; the engine restarted for only about 30 seconds until it lost all power again. The pilot then maneuvered the airplane towards a road for a forced landing, but the airplane impacted treetops. The airplane came to rest upright on a riverbank. Figure 1.Google Earth map depicting flight route of the accident airplane The airplane came to rest about 10 nm east of WA77. The wings, fuselage, engine, and empennage were impact damaged. First responders reported no evidence of a fuel spill and, by removing the fuel caps, observed fuel odor in the right-wing fuel tank as well as some fluid consistent with aviation gas; they were not able to confirm if the left- wing tank had fuel. The fuel selector was documented in the OFF position. The pilot stated that he switched the fuel valve lever to the OFF position before egressing. Less than a gallon of fuel was retrieved from the fuel tanks during wreckage recovery. Postaccident examination of the airplane and engine did not reveal any preimpact mechanical anomalies. The fuel system was traced from each wing tank to the carburetor. The fuel selector rotated normally and was unobstructed. The fuel lines that had not been damaged from impact or removed to transport the airplane were secure. Mechanical continuity was established throughout the rotating group, valvetrain and accessory section as the crankshaft was manually rotated at the propeller by hand. Thumb compression was achieved at all four cylinders and the valves displayed normal lift when the crankshaft was rotated. Examination of the cylinder’s combustion chamber using a lighted borescope revealed normal piston face and valve signatures, and no indications of a catastrophic engine failure. According to the pilot, the fuel burn for the airplane was about 12 gallons per hour and he calculated that he would have about three hours of flight time. The fuel calculations revealed that, at the time of the engine power loss event, the airplane was flying for a total of about 2.8 hours and would have consumed about 42 gallons of fuel. The accident airplane had a fuel capacity of 40 gallons. The pilot did not provide his fuel calculations as requested. The accident airplane was not refueled at R49.