Cheneyville, LA, USA
N9184Q
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.
HISTORY OF FLIGHTOn August 2, 2022, about 1146 central daylight time, an Air Tractor AT-502, N9184Q, was substantially damaged when it was involved in an accident near Cheneyville, Louisiana. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 137 aerial application flight. The operator reported that the pilot was scheduled that day to disperse 7 loads of urea fertilizer over 2 jobs. He had completed the first job, spraying 5 loads, and was on his last load of the second job at the time of the accident. Data downloaded from the onboard SatLoc G4 GPS receiver revealed that, near the end of the flight, the airplane descended to about 11 ft mean sea level (msl) while flying on an easterly heading at 147 mph groundspeed. The airplane then began a climbing left turn as its airspeed decreased. The last recorded data point, which was approximately 1,300 ft west-southwest of the accident site, indicated that the airplane was about 200 ft msl, on a northeast heading, and the groundspeed was 128 mph. Further review of the GPS data revealed that, during the 24 times the pilot made an initial climbing left turn following a spray pass, the airplane reached an average altitude about 200 ft msl. A 1-minute video of the accident sequence taken from a truck driving south on a nearby highway showed the airplane coming into view on the right side of the screen (west side over the trees that bordered the highway). While climbing, the airplane flew over the southbound lanes then the northbound lanes. The airplane was lost briefly from view, then could be seen descending steeply. The airplane was momentarily lost from view during the descent and immediately before impact white smoke could be seen trailing the airplane. One witness reported seeing the airplane bank left, then perform a “barrel roll” to the left. Briefly at the start of the barrel roll he noted a “quick puff” of white smoke. The airplane then nosed down and impacted the ground. He added that the smoke did not continue to ground contact. Another witness reported, “…the [airplane] went belly up and then rolled to head straight into the ground.” PERSONNEL INFORMATIONAccording to records provided by the operator, the pilot received 40 total hours of agricultural flight training in PA-18-150, PA-25-235, and 7GCAA aircraft. He also completed 5 hours of ground school and received a record of training documenting his flight and ground training on November 10, 2021. The document specified that he was qualified to serve as pilot-in-command in agricultural aircraft operations. The operator reported that, because the pilot’s only agricultural flight training was performed in reciprocating engine-powered airplanes, he received additional agricultural training in a turboprop-equipped airplane. The pilot’s logbook reflected that he received 5 hours of dual training in an Ayres Corporation S2R-T34 over the course of two flights on two separate days in November 2021. The pilot’s logbook also reflected 4.9 hours in a Pilatus PC12. Since being hired by the operator in mid-July 2022, the pilot was only allowed to disperse fertilizer, which was done at a higher altitude than chemical dispersal. Since July 17th, excluding the accident date, he flew the accident airplane about 19 hours, dispersing 61 loads of fertilizer. Excluding the flights on the accident date, the pilot had logged 28.4 hours total flight experience in turboprop-powered airplanes. The operator’s chief pilot reported that the pilot was taught the proper use of BETA, Reverse, and propeller overspeed procedures. He also indicated that he and the accident pilot had talked extensively about BETA as part of training and that it was only to be used when the tailwheel was on the runway. AIRCRAFT INFORMATIONThe airplane was powered by a 750 maximum continuous shaft horsepower Pratt & Whitney PT6A-34AG engine equipped with a Hartzell 3-blade, single-acting, hydraulically operated, constant speed propeller with feathering and reversing capabilities. The mechanical low-pitch stop and the hydraulic low-pitch stop settings of the propeller were specified to be between 17.9° to 18.1°, and about 13°, respectively. The beta range, which was below the hydraulic low-pitch stop, was from +13° to the mechanical reverse stop range, between -7.5° to -8.5°. The throttle quadrant mounted on the left side of the cockpit immediately forward of the single seat contained a power lever, propeller lever, starting control lever, and friction knob. The upper portion of the power lever contained a “thumb latch” that was required to be pushed forward to allow the power lever to be moved aft of the idle stop into beta and further aft into reverse. Located on the upper part of the center instrument panel was a caution light placarded, “PROP IN BETA RANGE”, which illuminated when a microswitch made contact with the fuel control unit cam box lever. The airplane was equipped with an electrically-operated stall warning system. It was also equipped with a cellular phone and a “Drift Finder” smoke system that contained an “activation button” or switch on the lower portion of the control grip. The cellular phone, along with a GoPro camera with enclosed and 2 loose SD cards that were in the pilot’s vehicle, were read out by the NTSB Vehicle Recorder Division. A review of the airframe maintenance records revealed there was no entry indicating the stall warning horn had been replaced since the airplane was manufactured. Although operational testing of the stall warning horn system was not part of the preflight inspection procedures of the Federal Aviation Administration-Approved Airplane Flight Manual, the chief pilot reported that he did check it as part of his preflight check and he believed it was operational in the accident airplane. He also indicated that, when he flew the accident airplane, he never experienced illumination of the “PROP IN BETA RANGE” bulb with the power lever at idle. METEOROLOGICAL INFORMATIONAccording to the NTSB Meteorology Specialist’s Factual Report, there was no significant windshear identified below 15,000 ft. AIRPORT INFORMATIONThe airplane was powered by a 750 maximum continuous shaft horsepower Pratt & Whitney PT6A-34AG engine equipped with a Hartzell 3-blade, single-acting, hydraulically operated, constant speed propeller with feathering and reversing capabilities. The mechanical low-pitch stop and the hydraulic low-pitch stop settings of the propeller were specified to be between 17.9° to 18.1°, and about 13°, respectively. The beta range, which was below the hydraulic low-pitch stop, was from +13° to the mechanical reverse stop range, between -7.5° to -8.5°. The throttle quadrant mounted on the left side of the cockpit immediately forward of the single seat contained a power lever, propeller lever, starting control lever, and friction knob. The upper portion of the power lever contained a “thumb latch” that was required to be pushed forward to allow the power lever to be moved aft of the idle stop into beta and further aft into reverse. Located on the upper part of the center instrument panel was a caution light placarded, “PROP IN BETA RANGE”, which illuminated when a microswitch made contact with the fuel control unit cam box lever. The airplane was equipped with an electrically-operated stall warning system. It was also equipped with a cellular phone and a “Drift Finder” smoke system that contained an “activation button” or switch on the lower portion of the control grip. The cellular phone, along with a GoPro camera with enclosed and 2 loose SD cards that were in the pilot’s vehicle, were read out by the NTSB Vehicle Recorder Division. A review of the airframe maintenance records revealed there was no entry indicating the stall warning horn had been replaced since the airplane was manufactured. Although operational testing of the stall warning horn system was not part of the preflight inspection procedures of the Federal Aviation Administration-Approved Airplane Flight Manual, the chief pilot reported that he did check it as part of his preflight check and he believed it was operational in the accident airplane. He also indicated that, when he flew the accident airplane, he never experienced illumination of the “PROP IN BETA RANGE” bulb with the power lever at idle. WRECKAGE AND IMPACT INFORMATIONThe airplane impacted the off-ramp of a highway on a magnetic heading of 164°, slid about 52 ft, and came to rest upright on a heading of 341° magnetic. The engine assembly with attached propeller was separated from the structure and was located about 33 ft along and 7 ft to the right of the energy path. A smell of fuel was noted at the accident site despite heavy rain between the time of the accident and NTSB arrival the next day. There was no evidence of in-flight or postcrash fire on any component. The hopper, cockpit, both wings, empennage, both horizontal stabilizers and elevators, and engine and propeller assembly exhibited extensive impact damage. The right wing exhibited far greater damage than the left wing. All primary and secondary flight control surfaces remained attached or were in the immediate vicinity of the accident site and there was no evidence of preimpact failure or malfunction of the actuation mechanism or the control surfaces for roll, pitch, and yaw. The flaps were retracted and the flap droop system was continuous. The stall warning vane switch was separated from the leading edge and found inside the left wing. The stall warning horn electrical circuit remained intact except for impact damage to an electrical wire at the wing root and at a terminal of the stall warning horn, which remained installed in the displaced instrument panel. Although only slight abrasion was noted on the face of the horn, it did not operate during electrical testing. The horn was retained for examination by the NTSB Materials Laboratory. Examination of the cockpit, which was structurally compromised, revealed a yellow-colored plastic RainX bottle was on the left side under the seat, resting against the 1.5-inch-diameter aileron torque tube. Above the aileron torque tube was the elevator forward pushrod assembly, which was 0.75 inch in diameter. The RainX bottle trigger was separated and found among the wreckage, while one side of the bottle exhibited a dent near the bottom about 2 inches in diameter. Examination of the throttle quadrant, which was impact damaged and rotated from its normal position, revealed that the power lever was in beta range and the anti-reverse lock plate assembly was impact damaged. The propeller control was midrange, the condition lever was at flight idle, and the friction was tight. The thumb latch of the power lever operated satisfactorily during postaccident inspection and operational testing. The throttle quadrant and “PROP IN BETA RANGE” bulb holder and bulb were retained for further examination. Examination of the separated engine and fuel control unit, as well as examination and operational testing of the constant speed propeller governor, beta valve, and overspeed propeller governor revealed no evidence of preimpact failure or malfunction that would have precluded normal operation. Examination of the propeller that revealed all blades exhibited gouges on the leading edge. The No. 1 blade exhibited a gentle slight forward bend while blade Nos. 2 and 3 were fractured at different locations and were bent opposite the direction of rotation. The leading edge of the No. 3 blade was also twisted towards low pitch. An impact mark in the piston was associated with the propeller being at 21° blade angle, which was above the mechanical low-pitch stop setting. There was no evidence of propeller assembly preimpact failure or malfunction. X-ray images of the stall warning horn revealed that one group of strands appeared unbundled and a separated strand was visible. The filament of the “PROP IN BETA RANGE” bulb was intact and stretched. Examination of the throttle quadrant revealed one corner of the anti-reverse lock plate assembly was bent upwards with a corresponding contact mark on the aft side of the power lever.
The pilot’s loss of control after exceeding the airplane’s critical angle of attack for reasons that could not be determined.
Source: NTSB Aviation Accident Database
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