Cessna 172 accident near Coolin, Idaho, September 10, 2017

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

The pilot reported that he completed a normal landing to the south at a grass airstrip near a lake that was surrounded by 75-ft-tall pine trees. He added that he and his passengers ate lunch at the airstrip, and during that time, he noticed "mostly calm" wind with an "occasional gust from the south." The pilot further reported that, due to the runway gradient, he decided to take off downhill to the north because the wind sock was indicating a calm wind. He reported that, during the soft field takeoff, the takeoff roll was normal, but that, about 100 ft above ground level, he noticed that the "climb had slowed" and the "airspeed was dropping." The pilot lowered the nose, the airplane "descended quickly," and then touched down on the runway with about 30 ft remaining. Subsequently, the airplane overran the runway, crossed a road, and impacted a dumpster and trees. The fuselage and both wings sustained substantial damage. The pilot reported that the airplane was 25 lbs under maximum gross weight. The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. An automated weather observation station (AWOS) 13 nautical miles from the accident site, reported, about the time of the accident, wind from 240° at 6 knots. A review of four hourly AWOS recordings, south and east of the accident site, around the time of the accident, revealed that the wind was variable from the southwest to west at 5 to 10 knots, gusting 15 to 18 knots. The pilot reported that the takeoff was on runway 33. The calculated density altitude was 3,700 ft. According to the Federal Aviation Administration (FAA) density altitude Koch Chart, the airplane would have likely experienced a 32% decrease in the normal climb rate and a 50% increase in the normal takeoff distance. The FAA's Pilot's Handbook of Aeronautical Knowledge, FAA-H-8083-25B, contained a section titled, "Effect of Obstructions on Wind," which stated in part: "Another atmospheric hazard exists that can create problems for pilots. Obstructions on the ground affect the flow of wind and can be an unseen danger. Ground topography and large buildings can break up the flow of the wind and create wind gusts that change rapidly in direction and speed. These obstructions range from man-made structures, like hangars, to large natural obstructions, such as mountains, bluffs, or canyons. It is especially important to be vigilant when flying in or out of airports that have large buildings or natural obstructions located near the runway. The intensity of the turbulence associated with ground obstructions depends on the size of the obstacle and the primary velocity of the wind. This can affect the takeoff and landing performance of any aircraft and can present a very serious hazard." It is likely that, during the initial climb in high-density altitude conditions, the airplane encountered a quartering tailwind gust as the airplane climbed above the trees, which resulted in a loss of lift and an inability to gain altitude during the initial climb.

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.