One of the planes involved in the fatal Sept. 17 collision over Boulder County was not transmitting a required tracking broadcast during its flight, according to a preliminary report from the National Transportation Safety Board.
Three men — identified by the Boulder County Coroner’s Office as Daniel Wilmoth, 22, Samuel Fisher, 23, and Henry Butler, 69 — died in the collision involving a Cessna 172 and an amateur-made Sonex Xenos aircraft.
Both planes were within Denver International Airport airspace that required automatic dependent surveillance broadcast (ADS-B) “out” transmissions, a surveillance and tracking data signal, but according to the report, the Sonex did not transmit that data during the flight.
The Cessna was transmitting the data, the reports states.
On the morning of the crash, the Cessna, which was registered as a pilot school plane and had two occupants, took off from Rocky Mountain Municipal Airport in Denver at 8:43 a.m., and the Sonex departed from Platte Valley Airpark in Hudson at 8:38 a.m. The crash happened at 8:53 a.m., according to the report.
Both planes had climbed to about 7,000 to 7,500 feet and were flying toward the Longmont area, the Cessna northbound and the Sonex westbound, when the Cessna made a 360-degree turn before turning eastbound.
The flight track data of the two planes then merged and showed the two planes “rapidly descending,” the report states. Fragments sections of both planes’ left wings were found below the point where the flight tracks merged.
The planes then hit the ground nose-down. The main wreckage site of the Cessna was in a field about 1,800 feet southeast of the wing fragments in the 10000 block of Niwot Road. The main wreckage site of the Sonex was about 1,100 feet southwest of the wing fragments in the 9700 block of Niwot Road.
The Boulder County Sheriff’s Office, sheriff’s search and rescue, the coroner’s office, Mountain View Fire, Boulder Rural Fire Rescue, Boulder Emergency Squad, the State Patrol, the state Department of Transportation, Lifeline Helicopters, the Federal Aviation Administration and the National Transportation Safety Board responded to the crash.
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