Accident Overview
On May 10, 2015, at approximately 0911 central daylight time, an Air Tractor AT-502 airplane, registration N879JA, collided with terrain during a forced landing following a partial loss of engine power shortly after takeoff from Dighton Airport, Dighton, Kansas. The commercial pilot, the sole occupant, was not injured. The airplane, registered to and operated by Jordan Air Inc., was substantially damaged. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a positioning flight without a flight plan. Day visual meteorological conditions prevailed for the cross-country flight destined for Dodge City Regional Airport, Dodge City, Kansas.
Pilot Report and Events
The pilot reported that no anomalies were observed during the preflight inspection or before-takeoff engine runup. The airplane had been last fueled (topped off) a couple of days earlier at another airport and was not refueled before the accident flight. During takeoff from runway 35, the engine produced full torque and speed. Shortly after liftoff, the pilot made a left turn to avoid a powerline located about 400 yards north of the runway. Shortly after an initial power reduction during initial climb, the airplane experienced a partial loss of engine power. Corrective actions did not restore full engine power, prompting a forced landing to a nearby muddy field. The pilot reported that the engine continued to run after the accident, with a gas generator speed of about 35%. The engine was stopped by turning off the electric fuel pump, repositioning the fuel valve to OFF, and moving the condition lever to the fuel cutoff position.
Post-Accident Examination
On May 11, 2015, a Federal Aviation Administration (FAA) maintenance inspector from the Wichita Flight Standards District Office examined the wreckage, which had been recovered to the departure airport. The right wing, aft fuselage, and tail were substantially damaged during the forced landing. A fuel sample from the fuel control unit inlet filter revealed evidence of water contamination. Additional fuel samples from both wing fuel tanks and the firewall-mounted primary fuel filter initially appeared free of water contamination on the day of examination; however, over the next two days, the samples became opaque with a yellow tint. The FAA inspector noted that the airplane was in an abnormal attitude when the wing tanks were drained, so the samples were likely not representative of fuel at the lowest point of each wing tank in a normal ramp attitude. On May 13, 2015, the wreckage salvage company reported contaminated fuel with an orange/red color in both wing tanks and the firewall-mounted primary fuel filter. An engine examination revealed no evidence of a mechanical malfunction that would have precluded normal operation.
Laboratory Analysis
At the request of the National Transportation Safety Board (NTSB) investigator, the salvage company obtained fuel samples from the header tank and the fuselage-mounted primary fuel filter. These samples were submitted to the National Institute of Standards and Technology's Applied Chemicals and Materials Division in Boulder, Colorado, for testing. Visual examination revealed two immiscible liquid phases: a top phase consistent with a hydrocarbon and a bottom phase appearing aqueous. The top and bottom layers of the header tank sample were clear and colorless. The top layer of the primary fuel filter sample was clear and colorless, while the bottom layer was pale brown or orange with fine precipitate. Initial boiling temperatures indicated the bottom layer was water and the top layer was aviation turbine fuel. Volatility measurements using the advanced distillation curve (ADC) method confirmed the top hydrocarbon layer as aviation turbine fuel. Water concentration was about 162 parts per million (ppm) and 160 ppm for the hydrocarbon layers of the primary fuel filter and header tank samples, respectively—exceeding the specified limit of 30 ppm. The lower aqueous layers were consistent with water, with water concentrations of about 93% and 100% for the primary fuel filter and header tank samples, respectively.
Flight Manual Requirements
The Air Tractor AT-502B Airplane Flight Manual specifies that during a preflight inspection, a pilot should obtain a fuel sample from both wing fuel tank sumps, the header fuel tank sump, and the fuel valve sump.