David City, NE, USA
N2033N
AIR TRACTOR AT602
The commercial pilot was performing an aerial application flight when the airplane struck the ground in a right wing low, 60° nose-down attitude. Flight track data from an onboard aerial guidance system revealed that the airplane had completed 6 previous aerial applications that morning, and was engaged in a seventh application when the accident occurred. During the last application, the airplane made 4 passes followed by shallow turns to reverse direction. During these turns, the airplane climbed until it reached 90° abeam the direction of application, then descended as it completed the turn on the opposite heading. The accident occurred during the turn between the fourth and fifth passes. Postaccident examination of the airframe, engine, and propeller revealed no evidence of any mechanical malfunctions or anomalies that would have precluded normal operation. The flap actuator was found extended 3-7/8 inches, correlating to a flap extension of 30°. Based on the recorded data, the characteristics of the airplane's last turn before impact did not vary greatly from that of the other turns performed during the accident flight. It is likely that, during the turn, the pilot allowed the airspeed to decay and the airplane exceeded its critical angle of attack, which resulted in an inadvertent aerodynamic stall at an altitude which did not allow for recovery.
On July 28, 2016, about 1530 central daylight time (CDT), an Air Tractor AT-602, N2033N, impacted A corn field 3 miles northeast of David City, Nebraska. The pilot, the sole occupant on board, was fatally injured. The airplane was destroyed. The airplane was registered to Rayne Aviation, LLC, and operated by Emrich Aerial Spraying, LLC, both of Dorchester, Nebraska, under the provisions of 14 Code of Federal Regulations (CFR) Part 137 as an aerial application flight. Visual meteorological conditions (VMC) prevailed at the time, and no flight plan had been filed. The flight originated from Columbus Municipal Airport (OLU), Columbus, Nebraska, about 1430. According to Federal Aviation Administration (FAA) inspectors who were on-scene, the airplane had been spraying Headline® Fungicide (pyraclostrobin – a Group 11 fungicide) on a corn field. The accident site was located 200 feet north of County Road 38 and west of County Road O. There was no fire and there were no witnesses to the accident. The on-scene evidence was consistent with the airplane striking the ground in a right wing slightly low, 60° nose-down attitude. The airplane rebounded about 20 feet from the initial impact point and came to rest upright facing south. Witness marks in the field were consistent with a large sweep of the right wing through the corn crop, consistent with some right wing-down rolling motion at impact. All impact signatures and crop damage were in a northerly direction, and the debris field was small. The aft cockpit wall immediately behind the pilot's seat was deformed. Elevator and rudder control continuity was confirmed. Aileron controls were found to be continuous except for fractures at both wing roots. All hardware was found to be properly installed. The Hobbs Meter was destroyed. The airplane was equipped with an inflatable restraint system, and it had deployed. The airplane was equipped with an inflatable restraint system and it had deployed. The flap actuator was found extended 3-7/8". According to Air Tractor, this setting correlated to a flap deflection of 28° to 30°. Examination of the engine revealed the fuel control unit (FCU) low pressure fuel filter had dark colored debris on the filter and in the bottom of the filter bowl. The FCU high pressure fuel filter had a chalky gray sediment in the housing. The propeller assembly had fractured off the engine propeller shaft on impact. Two blades remained attached. The other three blades had broken off the hub. One blade was found near the propeller assembly, a second blade was found in front of the fuselage, and the third blades was found several weeks later in a corn field some distance from the main wreckage. On August 18, 2016, FAA and Pratt & Whitney examined the airplane, engine, propeller, and fuel system at the facilities of Dodson International in Rantoul. Kansas. According to Pratt & Whitney, the engine displayed contact signatures to its internal components, characteristic of the engine making significant power at impact. Engine components displayed no indications of malfunction or pre-impact failure. Examination of the recovered propeller blades and propeller hub bore no indications that the propeller may have been in Beta mode or reverse pitch. On December 1, 2016, the propeller assembly was further re-examined under the auspices of two FAA inspectors at the facilities of Stallings Aircraft Propeller in Wynne, Arkansas. Representatives from Hartzell Propellers and Air Tractor were in attendance. According to Hartzell's report, blade butt, piston, cylinder, and rod impact marks indicated the propeller was operating at a blade angle range of approximately 16° to 19° at impact. The beta ring low pitch for this propeller is 13.9° and the "hydraulic" (aka "running") low pitch is approximately 7.9°. The estimated blade angle at impact was above the low pitch stop and in the normal operating range. The report concluded, "There were no discrepancies noted that would prevent or degrade normal propeller operation prior to impact. All damage was consistent with high impact forces with objects and/or terrain." A SATLOC (an aerial guidance system that allows aerial applicators to view flight information, such as spray and waypoints, and companies to track the position of their aircraft) was recovered from the wreckage and sent to NTSB's Vehicle Recorder Division for download and readout. According to the GPS Specialist's factual report, the airplane had made six previous aerial applications that morning, and was engaged in a seventh application when the accident occurred. During this last application, the airplane made four passes followed by shallow turns in the opposite direction. During these turns, the altitude increased until the airplane reached 90° abeam the direction of application and descended as it completed the turn on the opposite heading. The last data point was captured at 15:03:57 as the aircraft was turning to complete its fifth pass. The recorded altitude showed the aircraft was at 1,841 feet msl and at a groundspeed of 96 miles per hour. The spray condition was off. The measured diameter of the airplane's last turn, from the impact point to a point abeam the impact point, was measured to be approximately 750 feet. The diameter of the previous turns throughout the entire accident flight ranged from 600 feet in diameter to over 1,000 feet in diameter. Based on the recorded data, the characteristics of the airplane's last turn prior to impacting the field did not greatly vary from other turns the airplane performed during the accident flight. According to the SATLOC manufacturer, up to six seconds of data may be lost in the volatile memory during a high impact. According to an Arkansas Air Tractor pilot familiar with this accident, agricultural pilots often make turns with flaps extended to give the airplane greater stability. He said, "Most all the Air Tractors need flaps in turns when carrying a load. There are 3 notches of flaps in the AT-602: 15, 30 and 45°. Most Air Tractor pilots use 30° of flaps and keep their speed above 100 knots. There are some pilots who use 45° but let the airspeed get down to 80 to 90 knots in turns. There are other pilots who do wing-over turns. Some pilots pull their stall warning circuit breaker on the panel to keep it from annunciating during the turn. This 'on the edge' kind of flying is just a bad combination that gets worse as the weather warms up and the density altitude climbs." The pilot's autopsy report attributed death to "massive blunt trauma secondary to a plane crash." His toxicology report revealed no evidence of carbon monoxide, ethanol, or drugs. Cyanide testing was not performed.
The pilot’s exceedance of the airplane’s critical angle of attack while maneuvering at low altitude, which resulted in an aerodynamic stall and impact with terrain.
Source: NTSB Aviation Accident Database
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