CEN17FA050

The pilot exceeded the airplane's critical angle of attack while maneuvering at low altitude, which resulted in an inadvertent aerodynamic stall and subsequent impact with terrain.

The commercial-rated pilot and commercial pilot-rated crewmember were working with a ground crew in animal damage management. These flights typically begin with the surveillance, about 75 to 100 ft agl. Upon identifying a target, the airplane will descend to between 20 and 40 ft agl so that the crewmember can shoot the target. The ground crew lost contact with the airplane about 2 hours into the operation. The airplane wreckage was later located in steep, hilly terrain. Based upon the location of the wreckage and witness statements from the ground crew, it is likely that the airplane was conducting a low-altitude predator mitigation pass at the time of the accident. Damage to the airplane, witness marks at the accident site, and the position of the wreckage were consistent with the airplane impacting terrain in a nose-low attitude, consistent with an aerodynamic stall and subsequent impact with terrain. An examination of the airframe, engine, and related systems revealed no anomalies that would have precluded normal operations. It is likely that, while maneuvering at a slow speed, the pilot exceeded the airplane's critical angle of attack, which resulted in an aerodynamic stall at an altitude too low for recovery.

Weather conditions recorded at the Yellowstone Regional Airport (COD), Cody, Wyoming, located 38 miles northwest of the accident site at 0953 were: wind 350° at 8 kts, visibility 10 miles, sky condition 6,500 ft overcast, temperature -13° C, dewpoint temperature -19° C, altimeter setting 30.35 inches of mercury. Weather conditions recorded at WRL, located 28 miles southeast of the accident site at 0953 were: wind 340° at 8 kts, visibility 10 miles, sky condition 6,000 ft overcast, temperature -13° C, dewpoint temperature -18° C, altimeter setting 30.57 inches of mercury. Pilot Information The pilot was based in Worland, Wyoming, and had initially started working for the USDA APHIS as a flight crewmember (gunner) in 2007. In March of 2016, he started flying for the program as a pilot. He completed his initial flight training, at the USDA flight training center, in May of 2016, in Cedar City, Utah. He then moved to the field to continue the remainder of the training program which was scheduled to last for a year. During this time the pilot would fly with an instructor pilot and experienced flight crewmember; in this case, the same crew member injured in the accident. The accident flight was still within the year training program with the USDA APHIS. The USDA flight training officer in Cedar City reported that the pilot was level-headed with good character and one of the best pilots to come through the program. He had no concerns or reservations about the pilot or his ability to safely operate the airplane. Neither the State Director nor the ground crew that worked with the pilot expressed any concerns or reservations about the pilot or his abilities. Other Flight Crewmember Information The flight crewmember's medical certificate contained the limitations "must have available glasses for near vision." The flight crewmember was based in Worland, Wyoming, had been with the USDA APHIS for over 30 years, and a pilot for the USDA APHIS for at least 20 years. He was currently qualified as both a pilot and a flight crewmember (gunner) and served as a flight instructor for the region. Neither the State Director nor the ground crew that worked with the flight crewmember expressed any concerns or reservations about the flight crewmember's abilities. The flight crewmember was serving as both a flight instructor and a flight crewmember during the accident flight. He was the only instructor pilot in the program who had flown with the accident pilot in the field. His duties included familiarizing the pilot with the pilot responsibilities and reporting back to the training center on a regular basis regarding the pilot's performance. The airplane was purchased by the Wyoming Wool Growers Association in September 2016. The airplane then underwent alterations to configure the airplane for the animal damage management flights. These alterations included the installation of clear windshields, a skylight, "D" windows, and a right-side swing-up window. According to USDA personnel, the airplane was configured the same as the previous airplane flown by the pilot and flight crewmember. The airplane was equipped with a stall warning indicator which sounded a horn in the cockpit when the airplane approached the critical angle of attack. The airplane was not equipped, nor was it required to be equipped with a visual angle of attack indicator. The wreckage was located in steep hilly terrain, just below a ridgeline that extended from northeast to southwest, increasing in elevation to the south. The elevation at the accident site was about 4,400 ft mean sea level (msl). The airplane wreckage included the fuselage, empennage, both wings, and the engine and propeller assembly. The airplane came to rest in a ravine in a near-vertical, nose down attitude, with the right wing uphill and the left wing downhill. There was a strong smell of fuel on scene. The initial impact point was uphill and north northwest from the main wreckage. Yellow paint chips, the fragments from the green navigation light, vortex generators, and plexiglass were located at the crest and down the north side of the hill. The right wing exhibited accordion crushing along the leading edge from the wing root outboard to the forward strut. The entire span was crushed and buckled and the fabric was torn. The right aileron and right flap remained attached. The right flap was bent, buckled, and wrinkled along the entire span. The right aileron was bent down about 45° at the inboard portion of the control. The right aileron cables remained attached at the flight control and were continuous through the pulley inboard to the fuselage and to the flight control stick. The forward cable was separated at the fuselage and exhibited broomstraw signatures consistent with overload. The right trailing strut/aft strut was buckled about 8 inches outboard of the fuselage attach point. The right wing fuel tank was compromised. The pitot tube was clear of any visible contamination. The left wing exhibited accordion crushing along the leading edge, from the wing root outboard to about midspan. The entire span was crushed and buckled and the fabric was torn. The left aileron and left flap remained attached. The left aileron was bent, buckled, and wrinkled along the entire span. The left flap was unremarkable. The left aileron cable remained attached at the aileron and was continuous through the pulley inboard to the fuselage. The right main landing gear remained partially attached and was bent aft. The left main landing gear remained partially attached and was bent slightly outward. The fuselage from the baggage compartment, aft, to the empennage was unremarkable. The flight control cables and tubing were continuous and correctly rigged from the control stick aft to the elevator and rudder. The rudder and trim cables on the left side were cut for extrication purposes by first responders. The elevator trim measured 5 threads on the top and 10 threads on the bottom. According to CubCrafters, this position, for the entire horizontal stabilizer, was consistent with 1° leading edge up from takeoff position, also consistent with the airplane being flown at slower airspeeds, or an aft center of gravity. The fuselage remained attached to the empennage and both wings, and included the cabin and instrument panel. The left side of the fuselage was crushed inward and to the right. The right window and door were broken. The forward windscreen was fragmented. The left window and fuselage were impact damaged and cut further for extrication purposes. The instrument panel separated partially from the fuselage. The circuit breaker panel and switch panel did not provide any reliable readings. The propeller separated from the engine at the propeller flange and was partially buried in the ground directly beneath the wreckage. The blades were labeled "A" and "B" for identification purposes. Blade A was uphill. Blade B was downhill and covered in dirt/earth. Both blades were bent and twisted along their entire span and exhibited chordwise scratches along the face of the blade and a few leading-edge nicks. The spinner was crushed aft with rotational crushing and scoring. The airplane wreckage was recovered and relocated to a facility in Greeley, Colorado, for further examination. The forward lap belt and two-point shoulder harness remained buckled. The lap belt webbing was cut by first responders to aid in extrication of the pilot. The inertia reel functioned as designed when tested. The rear lap belt and two-point shoulder harness were not buckled. The inertia real functioned as designed when tested. The following was documented on the instrument panel: Airspeed Indicator - zero Attitude Indicator - inverted Vertical Speed Indicator - 1,650 fpm down Kollsman Window - 30.27 Altimeter - 9,000 ft Hobbs Meter - 67.1 The digital tachometer was powered by an external power supply and did not provide