Accident Overview
On May 28, 2020, at about 1600 Alaska daylight time, an Aero Commander 500S airplane, registration N909AK, sustained substantial damage during an accident near Aniak, Alaska. The pilot and three passengers received serious injuries. The flight was operated as a Title 14 Code of Federal Regulations Part 91 public aircraft flight, owned by the State of Alaska and operated by the Division of Forestry.
Pilot Actions
According to the pilot, after arriving in Aniak, he arranged for refueling by the local fuel vendor's ground service personnel. He signed the fuel receipt and then returned to the cockpit to complete paperwork. Afterward, he loaded passengers, started the engines, and taxied to Runway 29 for departure. Shortly after takeoff, during initial climb, he noticed what he initially thought was mechanical turbulence, followed by a reduction in climb performance and engine power loss. Unable to maintain altitude, descending at about 400 feet per minute, he selected an area of shallow water-covered terrain for an off-airport landing. The airplane sustained substantial damage during the landing.
Fueling Incident
The fueler reported unfamiliarity with the airplane. He asked the pilot where to attach the grounding strap and the location of the fuel filler port. Before refueling, he asked the pilot, "do you want Prist with your Jet?" to which the pilot responded negatively. After refueling, the fueler returned to his truck, wrote "Jet A" in the meter readings section of the prepared receipt, and presented it to the pilot, who signed it. The fueler later added "no Prist" to his copy. He did not see a fuel placard near the fueling port.
Postaccident Examination
A postaccident examination revealed that the reciprocating engine airplane had been inadvertently serviced with Jet A fuel. A slightly degraded placard near the fuel port on the top of the wing stated, in part: "FUEL 100/100LL MINIMUM GRADE AVIATION GASOLINE ONLY CAPACITY 159.6 US GALLONS."
Probable Cause
The official probable cause is: Loss of engine power after the aircraft has been refueled with an inappropriate fuel.