NTSB report: two planes touched wings before crashing and killing all onboard

The NTSB has released its preliminary report on a mid-air collision that happened in Boulder County last month. Two planes crashed along Niwot Road, killing three men. One plan was a Cessna 172S from a flight school, and the other was a Sonex Aircraft Xenos. 

The report says both planes were flying at about 7,000-7,500 feet, and were operating under visual flight rules. The Cessna turned eastbound, and the flight track data of the two planes merged, and then both planes rapidly descended. The report says that investigators found fragmented sections of the outboard left wings of both airplanes in a field below the point where the two flight tracks merged.

The report indicates that both airplanes were operating within the Mode-C veil of the Denver International Airport Class B airspace that requires automatic dependent surveillance broadcast (ADS-B) "out" transmissions. The Cessna was equipped with ADS-B "in/out" equipment, and did transmit ADS-B data. The Sonex did not transmit ADS-B data during the accident flight. ADS-B is used to detect and alert pilots to potential traffic conflicts.