NTSB: Plane in midair Colorado collision wasn't transmitting signal

Investigators say a homebuilt airplane that collided with another small plane last month in Boulder County, killing three people, wasn't automatically transmitting signals of its position as required for the airspace around Denver International Airport.

A preliminary report by the National Transportation Safety Board released Friday said both planes were required to transmit outgoing automatic dependent surveillance broadcast.

The transmissions provide continuous updates on a plane's location using navigation satellites to other planes and air traffic controllers.

The NTSB said the homebuilt plane hadn't transmitted such a signal since about two months before the crash. It said the second plane was transmitting the signals.

The crash took place along Niwot Road. The victims were identified as Daniel Wilmoth, 22, Samuel Fisher, 23, and Henry Butler, 69.