Air Tractor AT-602 N622AW accident near Oakland, Nebraska

Probable cause

The pilot’s failure to maintain coordinated flight during aerial-application operations, which resulted in fuel migration between the interconnected wing fuel tanks, and his failure to adequately monitor fuel levels during the flight which resulted in a loss of engine power due to fuel starvation when the right-wing tank became depleted of usable fuel.

NTSB analysis

The pilot was conducting an agricultural flight when there was a sudden loss of engine power during an aerial-application spray turn. The airplane’s aft fuselage was substantially damaged during the subsequent forced landing in a cornfield.

According to engine monitor data, as the aerial-application flight progressed, there was an overall decrease in fuel in the right-wing fuel tank and a minimal decrease of fuel in the left-wing fuel tank. The airplane’s wing fuel tanks are interconnected through a header tank and cannot be individually selected. As the flight progressed, the fuel imbalance increased until the right-wing tank was depleted of usable fuel and there was a sudden loss of engine power due to fuel starvation. The left-wing tank contained nearly 80 gallons of fuel at the time of the accident.

Examination of the airplane’s fuel system did not reveal any preimpact anomalies that would have precluded normal distribution of fuel from the fuel tanks to the engine. According to the airplane flight manual, fuel can migrate from one tank to the other if the airplane is flown uncoordinated or if all turns are made in the same direction. A postaccident examination confirmed that the airplane was equipped with a required cockpit placard that instructed pilots avoid skidding turns, which may result in fuel migration from one tank to another, that the engine may lose power when either tank becomes empty, and to monitor the fuel level in each tank frequently when the fuel level is less than ½ tank.

During the final 12 minutes of the flight, the engine monitor’s master caution parameter activated multiple times when the fuel level in the right-wing tank decreased below 11 gallons. The master warning parameter can be activated by several factors; however, at that time the recorded fuel level in the right-wing tank (less than 11 gallons) was the only parameter that would have activated the master caution. Additionally, the airplane’s low fuel warning system functioned normally when tested after the accident. As such, it is likely the pilot failed to notice or acknowledge the low fuel warnings that were presented in the cockpit during the flight.

Based on the available information, the pilot likely did not maintain coordinated flight during the aerial-application flight, which resulted in fuel migrating from the right-wing tank to the left-wing tank. Additionally, the pilot did not adequately monitor fuel levels during the flight which resulted in fuel starvation to the engine when the right-wing tank was depleted of usable fuel.

Text from the NTSB. Open the NTSB docket for CEN24LA272 for the full record.