Plane destroyed in mid-air collision over Boulder County was not transmitting location, investigators say

Space Accidents Investigations
Andrew Harnik/AP
The National Transportation Safety Board logo and signage are seen at a news conference at NTSB headquarters in Washington, Dec. 18, 2017.

A homebuilt airplane that collided with another small plane last month in northern Colorado, killing three people, was not automatically transmitting signals of its position as required for the airspace around Denver's airport, according to investigators.

A preliminary report on the Sept. 17 crash by the National Transportation Safety Board, released Friday, said both planes were required to transmit outgoing automatic dependent surveillance broadcast, or ADS-B, transmissions, which use navigation satellites to provide updates on a plane's location to other planes and air traffic controllers. Neither was required to be in radio contact with air traffic control, it said.

The Cessna 172 involved in the crash, which had a flight instructor and a student pilot on board, was transmitting its location but the Sonex Xenos, a light aircraft registered to Henry Butler, 69, was not and had not transmitted such a signal since about two months before the crash, according to air traffic records, the NTSB said. Also killed in the collision were Daniel Wilmoth, 22, and Samuel Fisher, 23.

The Xenos took off from Platte Valley Airpark at 8:38 a.m., about five minutes before the Cessna took off to the north from Rocky Mountain Metropolitan Airport, about 35 miles (56 kilometers) to the southwest of Platte Valley. The Xenos flew west and, after the Cessna turned east, their flight paths merged and both airplanes rapidly descended, the report said.