History of Flight
On November 16, 2021, at approximately 1836 mountain standard time, an Air Tractor Inc. AT-802A, registration N802NZ, sustained substantial damage in an accident near Estes Park, Colorado. The pilot received fatal injuries. The aircraft was operating under 14 Code of Federal Regulations Part 137 as an aerial firefighting flight, tasked with dropping chemical retardant on the Kruger Rock fire in mountainous terrain. The pilot was using night vision goggles during the flight.
Video footage showed the airplane's wings rocking as it approached the intended drop location. Two witnesses reported seeing the airplane roll inverted but did not observe its descent into terrain. One witness, in radio communication with the pilot, stated that no problems were reported and no distress calls were made before the accident.
Meteorological Information
The National Weather Service Surface Analysis Chart for 1700 depicted a low-pressure system over Nebraska with a cold front extending southwestward across northern Colorado to another low over northeastern Utah. A high-pressure system was over southwestern Colorado with a mesoscale ridge extending northeastward over the accident vicinity. The accident site was just south of the cold front in a strong pressure gradient. Station models showed west winds at 20 to 40 knots, clear to scattered clouds, and temperatures from 60°F ahead of the front to 39°F over southern Wyoming.
The 2000 chart showed the low had moved into eastern Colorado with the cold front located south of the accident site. Station models indicated west-northwest winds at 40 knots, scattered to broken skies west and northwest, and temperatures at 51°F east and 32°F northwest of the site.
The closest official weather reporting site was Vance Brand Airport (LMO) in Longmont, about 18 miles southeast at 5,055 ft elevation. The 1835 observation reported wind from 200° at 11 knots gusting to 17 knots, variable between 170° and 230°, visibility 10 miles or more, scattered clouds at 11,000 ft agl, temperature 17°C, dew point -8°C, and altimeter 29.78 inches of mercury. Observations at LMO showed west winds gusting 20-35 knots from 0955 to 1500, backing to southwest with decreasing speeds through 1600, then decreasing to less than 10 knots between 1600 and 1815, shifting to east. Winds shifted to south to west-southwest at 1835, increasing immediately before the accident, with gusts to 29 knots at 1915 before decreasing at 2115.
Remote Automated Weather Stations reported conditions near the accident site. Lily Lake (CO045) at 8,960 ft elevation, 3.3 miles southwest, at 1849: temperature 41°F, dew point 15°F, relative humidity 36%, wind 225° at 7 knots, peak gust 28 knots, max gust 38 knots at 1748. Estes Park (ESPC2) at 7,892 ft, 4.3 miles west-northwest, at 1824: temperature 44°F, dew point 21°F, relative humidity 39%, wind 260° at 11 knots, peak gust 28 knots, max gust 39 knots at 1424. Boulder County Fire (BCFC2) at 6,674 ft, 9.6 miles southwest, at 1742: temperature 51°F, dew point 19°F, relative humidity 28%, wind 280° at 7 knots, peak gust 32 knots, max gust 43 knots at 1642.
Satellite imagery from GOES-16 at 1836 showed low- to middle-level clouds west of the accident site in a north-south pattern similar to transverse banding or trapped lee waves, with a clear gap (foehn gap) over and east of the site, and enhanced higher clouds southeast. Transverse bands at high levels may indicate severe or extreme turbulence; at low levels, they often indicate a temperature inversion and directional shear. The foehn gap is a cloud-free zone from strong sinking on the lee side of a mountain barrier during mountain wave activity or strong downslope winds. GOES-17 imagery at 1836 showed similar transverse cloud patterns. Animation showed most clouds remained relatively stationary. Low cloud bands south of the site were consistent with rotor clouds, a turbulent formation in the lee of mountain barriers with high-speed crosswinds.
The NWS had SIGMET Uniform 15 for moderate to occasional severe turbulence below 18,000 ft due to strong low-level winds, and SIGMET Xray 4 for severe turbulence between 25,000 and 42,000 ft due to wind shear from jet stream and mountain wave activity. Graphic-AIRMET Tango was active for moderate turbulence from surface to 18,000 ft and low-level wind shear below 2,000 ft agl.
Wreckage and Impact Information
The airplane wreckage was upright and exhibited characteristics of a low-speed, nose-down impact with sloping, wooded terrain. No ground scarring preceded the wreckage. The wreckage did not show asymmetric wing damage consistent with yaw or bank on impact, and there was no lateral displacement of the empennage indicative of yaw. The fuselage, wings, and empennage sustained substantial damage. The propeller displayed torsional bending and twisting, indicating the engine was producing power at impact. Postaccident examination revealed no mechanical anomalies that would have precluded normal operation.
Flight Recorders
Data from the Flight Data Acquisition Storage and Transmission System showed decreasing indicated airspeed and increasing engine interstage turbine temperature, gas producer speed, propeller speed, engine torque, and fuel flow toward the end of the recording.
Medical and Pathological Information
The autopsy report determined the pilot died from multiple blunt force injuries. The Federal Aviation Administration Forensic Toxicology Report was negative for all tested substances.