Cessna 172 accident near Madras, Oregon, July 22, 2019

The NTSB's narrative final · quoted from the NTSB record

The flight instructor and her student departed on a local instructional flight. After completing a touch-and-go maneuver at a nearby airport, the student configured the airplane for a normal landing. The instructor’s attention was focused outside the cockpit as she watched for an incoming airplane while her student flew the airplane. While setting up for the approach, the student configured the airplane by applying carburetor heat and retarding the throttle. After the student turned on to final approach, she noticed the engine speed reduce to 1,000 rpm without any intervention. She slowly advanced the throttle but was unable to maintain altitude. The flight instructor then took control of the airplane and determined that they had lost partial engine power. The airplane subsequently impacted the ground hard and came to rest. A postaccident examination of the airplane revealed a small obstruction in the left-wing vent line, which is not likely to have obstructed fuel flow as the obstruction was not in the fuel lines and fuel was being fed to the engine from both tanks at the time of the accident. The engine was nearly 1,400 hours beyond the manufacturer’s recommended time before overhaul but did not show any preimpact anomalies during testing. Weather data indicated that the airplane was operating in conditions conducive to carburetor icing at the time of the accident and may have been more susceptible to icing because the engine was being fueled by automotive gasoline. However, the cause of the loss of engine power could not be determined as the student pilot applied carburetor heat before the power loss and postaccident testing did not reveal any anomalies with the airplane or engine.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.