Accident Sequence
On July 16, 2021, at about 1230 Alaska daylight time, a Cessna 172, registration N7137T, was operating as a personal flight under Title 14 Code of Federal Regulations Part 91. While en route, the engine experienced a partial loss of power. The pilot performed emergency checks according to the checklist and reported everything checking “good.” He decided to make a precautionary off-airport landing on a gravel bar in the Yetna River. After an uneventful landing, he conducted further checks, verifying control movements, fuel levels, and fuel sumps. Several run-ups confirmed the engine produced appropriate power within limits, and he prepared for takeoff.
During takeoff from the gravel bar, as the nose of the airplane lifted from the surface, the pilot applied additional flap to allow the airplane to become airborne. At that point, the engine again experienced a partial loss of power. The pilot rejected the takeoff by reducing power to idle, retracting flaps, and applying maximum brakes. The airplane encountered a “bump” that pitched the nose down. The pilot then made a hard right turn to avoid entering the water, causing the airplane to nose down. The left wing struck the ground, and the airplane came to rest upright. The pilot and passenger, who received minor injuries, exited the airplane without further incident. The airplane sustained substantial damage to the left wing.
Post-Accident Examination
A mechanic, under the supervision of a Federal Aviation Administration inspector, conducted a postaccident engine run. The mechanic noted that the engine ran roughly, leaked significant oil, and the exhaust system appearance was consistent with the engine “burning” significant oil. During startup, oil pressure immediately reached 35 pounds per square inch. At 1,700 rpm, the engine was “not smooth” but otherwise normal; magneto and carburetor heat checks were normal.
Later, under the supervision of a National Transportation Safety Board investigator, another mechanic performed a compression check. All cylinders except No. 2 showed compression; No. 2 had zero compression. The No. 2 cylinder was removed, revealing damage to the cylinder, piston, and rings. A hole was present in the piston behind the rings, and a portion of the piston head was fractured. The combustion dome of the No. 2 cylinder exhibited a slight sandblasted appearance.