UPDATE:
BOULDER, Colo. (AP) -- A small plane clipped the towline of another plane pulling a glider Saturday, sparking a fiery midair crash in Colorado and killing three people, authorities said.
The glider disconnected from its tow plane just before the collision that sent both planes plummeting to the ground, Boulder County sheriff's office spokesman Rick Brough said.
The glider landed safely - with no injuries to any of the three people on board - after the two planes made impact, authorities said.
"We understand the glider went through a fireball after the impact," NTSB field investigator Jennifer Rodi.
The crash occurred about 1:30 p.m. near the Boulder Municipal Airport.
"We heard a loud bang and looked up in the air and we saw what looked like a glider and big, black smoke right next to it," said witness Paul Aiken. "It looked like fireworks, the explosion."
The pilot of the glider was Ruben Bakker, according to his mother-in-law Deborah Tjarks, who spoke to The Associated Press. She said he saw the collision about to happen and released the glider and banked but still flew through a fireball. Bakker did not immediately return a call for comment.
Brough said one of the planes, a Piper Pawnee with just a pilot aboard, belonged to Mile High Gliding Inc. and had just taken off from the Boulder airport with the glider in tow shortly before the accident happened.
A woman who answered the phone at the glider company declined to comment.
The other plane, a single-engine, four-seat Cirrus SR20, was carrying two people.
Brough said the three people aboard the two planes were killed. He said there was initial concern that there could have been others aboard the Cirrus because of its number of seats but investigators were now "pretty certain" there were just the two aboard.
Gliders, or sailplanes, are lightweight aircraft that are often towed into the sky, then released to glide to the ground.
It was unclear why the Cirrus got close enough to the Piper Pawnee to clip its towline.
The crash spread debris over a 1 1/2 mile region, scorching several sections of prairie in the Rocky Mountain foothills. The crash happened near a suburban area dotted with homes and businesses, but no one on the ground was injured.
It was unclear from where the single-engine, four-seat Cirrus SR20 that clipped the tow line took off. Tail numbers were not immediately available.
An amateur video shot at the scene showed a plane on fire, floating to the ground trailing thick, black smoke and a parachute.
Brough said the parachute was designed to deploy if a plane was disabled and was attached to the plane's wreckage, not a pilot or passenger.
Brough said the identifications of the victims were being determined by the coroner's office and wouldn't be released until after families were notified.
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MSNBC is reporting that there has been a deadly mid-air plane collision near Boulder, Colorado.
UPDATE 6:08 PM -- LA Times reports 3 dead in the crash:
Witnesses reported hearing an explosion, and then seeing one of the aircraft plummet to the ground with a parachute attached. Wreckage was scattered in several locations.
AP has more details from an FAA spokesman:
The Federal Aviation Administration says a plane towing a glider and another aircraft collided in Colorado, killing at least two people.
FAA spokesman Mike Fergus says the glider, described as a sail-plane, apparently disconnected after the Saturday afternoon collision and landed safely a short time later.
Fergus says the two small planes crashed.
Witnesses reported smoldering wreckage in at least three areas on the prairie north of Boulder, which sits at the foothills of the Rocky Mountains.
Aquina Rogers, a worker at a storage facility in the area, said she could see a wing in one of the wreckage fields.
Watch MSNBC's report below. Story developing:
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