Air Tractor Inc AT-502 N4556S accident near Firebaugh, California

Probable cause

The pilot’s decision to continue the takeoff after the engine stopped producing its full-rated torque while operating in high-density altitude conditions and his subsequent failure to maintain clearance from the power transmission wires.

NTSB analysis

The pilot ferried the airplane to a private ag-operating airstrip where it was fully fueled, and 400 gallons of defoliant were loaded in the hopper. During the takeoff roll for the aerial application flight, the pilot noticed that the engine was not producing its full-rated torque, but he chose not to abort the takeoff. The pilot reported that, when the airplane reached the end of the runway, it lifted off but would not climb out of ground effect. As the airplane approached power transmission wires about 0.5 mile from the airstrip, the pilot began dumping the defoliant load to gain altitude. Dumping the load resulted in the airplane gaining some altitude, but, simultaneously, the airplane's nose pitched up, which increased drag and stopped the climb. The airplane struck the wires and landed hard in an open field. Postaccident examination of the engine found no preimpact mechanical anomalies that would have precluded normal engine operation. It is likely that the engine was not producing its full-rated torque because the density altitude was 2,400 feet (as compared to the field elevation of 236 feet), which reduced the available engine torque.

Text from the NTSB. Open the NTSB docket for WPR12LA433 for the full record.