ERA22FA350 · Air Tractor Inc AT-502

The pilot was performing an aerial application flight in the turboprop-equipped airplane. Data from an onboard GPS and witness statements indicated that the pilot completed a spray pass, entered the airplane into a climbing left turn to about 200 ft, and the airplane rolled and descended steeply to ground contact. Witness statements and video revealed that smoke could be seen briefly emitting from the airplane before impact. Postaccident examination of the airplane and engine revealed no evidence of mechanical malfunctions or anomalies that would have precluded normal operation, and there was no evidence of pre- or post-impact fire. The observed smoke may have been the result of the pilot inadvertently engaging the smoke button or switch on the bottom portion of the control grip. Although the filament of the “PROP IN BETA RANGE” lightbulb was stretched consistent with being in a ductile state at impact, the power control lever was at or forward of the idle stop and the propeller blade angle was 21°, which was above the mechanical low-pitch stop and well above the beta range. Additionally, there was no evidence of preimpact failure or malfunction of the engine, propeller, constant speed propeller governor including beta valve, or power control lever at the throttle quadrant. The damaged internal engine components, the fractured propeller blades, and the blade bending in the thrust direction and also opposite the direction of rotation, were consistent with the propeller operating with moderate power at impact and at a positive blade angle above the mechanical low-pitch stop. The electrically-operated stall warning horn was inoperative during postaccident electrical testing. It could not be determined whether the stall horn was operative during the accident flight. A plastic bottle found in the cockpit displayed damage on one side that was slightly larger in diameter than the diameter of an adjacent aileron flight control torque tube and much larger than the diameter of an adjacent elevator push rod assembly. It could not be determined from the available evidence if the bottle created any issue or distraction, but it is likely that the pilot would have been able to overcome any interference the bottle could have created with the aileron or elevator flight controls. Based on the available evidence, it is likely that following a spray pass and climbing left turn, the pilot exceeded the airplane’s critical angle of attack for reasons that could not be determined, which resulted in an aerodynamic stall and loss of control at an altitude too low for recovery.

Verbatim NTSB analysis and probable cause from the NTSB dataset