BOULDER, Colo. -- Two small planes collided in flames over Boulder's outskirts and killed all three people aboard, while a glider under tow by one aircraft cut loose and flew through the fireball to safety, officials and witnesses said.

Three people were aboard the glider that managed to disconnect from a Piper Pawnee as a Cirrus SR20 clipped the tow line an instant before the two planes collided, Boulder County sheriff's office spokesman Rick Brough said.

Both aircraft plummeted toward the ground but the glider landed safely with no injuries to anyone on board.

"We understand the glider went through a fireball after the impact," said NTSB field investigator Jennifer Rodi.

Sunday, friends of the glider pilot, Rueben Bakker, told TheDenverChannel.com that he is a hero.

"He was a hero. It's literally a game of seconds up there," said David Campbell, who owns Mile High Gliding.

The Piper Pawnee with only a pilot aboard belonged to Mile High Gliding Inc. and had just taken off from the Boulder airport with the glider in tow.

The Boulder County coroner's office identified the Piper pilot on Sunday as Alexander Howard Gilmer, 25, of Evergreen. The pilot of the Cirrus was Bob Matthews, 58, of Boulder, and his brother, Mark, 56, of Englewood, was his passenger.

Federal, state and local search teams walked a two-mile grid near the crash site on Sunday and recovered some evidence.

The pilots of the two planes were not required to talk with air traffic controllers.

Radar shows the Cirrus SR-20 left Boulder at about 12:45 p.m. Saturday and was lost for about 10 minutes, then showed up descending down to 8,300 feet when radar was lost again.

The National Transportation Safety Board can't yet say who may have been at fault. It also wasn't immediately known how the Cirrus got close enough to the Piper Pawnee to clip its towline.

"We’ll have to take into consideration the sun angles, the cloud angles, the visibility, and, unfortunately, we may not be able to answer factually where the pilots were looking just prior to the collision," Rodi said.

Investigators plan to talk to other pilots to determine whether they heard any communications between two small planes just before the in-flight collision.

With no black box data, investigators are relying heavily on video, photos and witnesses' testimony to determine what led to the fiery crash, Rodi said. The Cirrus had the capability to provide data from avionics, like a black box, but the avionics were destroyed in the crash and fire, Rodi said.

The crash occurred about 1:30 p.m. Saturday near the Boulder Municipal Airport over a suburban area dotted with homes and businesses. No one on the ground was injured.

"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," Paul Aiken told Boulder's Daily Camera. "It looked like fireworks, the explosion."

The Denver Post quoted Sue Patton, 53, as saying she saw two people plunge out of a plane.

"The plane was burning really strong," she said. "They really didn't have a choice."

Rob Zimmerman, who was outside nearby American Legion Post 10, told the paper he saw one person come from the aircraft.

Bakker's mother-in-law, Deborah Tjarks, told The Associated Press that Bakker saw the collision about to happen and released the glider and banked but still flew through the flames.

Bakker told 7NEWS on Saturday night that he barely missed the airborne wreckage when he cut loose from the plane.

"My passengers could feel the heat from the flames," Bakker said.

Bakker said he circled several times to see if he could assist the other planes somehow, but by then it was too late. He and his passengers, a woman celebrating her birthday and the woman's son, landed safely.

The other plane, a single-engine, four-seat Cirrus SR20, was carrying the Matthews brothers. It was unclear where the Cirrus took off.

The Matthews family issued a statement Sunday, saying, "Mark and Bob were men who were dearly loved. Wherever they went, they impacted their community with their integrity, kindness, humor and love. They will be sorely missed by their adoring wives, children and family and friends."

Brough said there was initial concern that others were 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.

Patton said she watched as one of the planes spiraled downward with a plume of black smoke billowing from it and a parachute deployed.

"It was kind of a slow-motion thing," Patton said. "It was surreal."

An amateur video shot at the scene also 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.

The crash spread debris over a 1 1/2 mile region, scorching several sections of prairie in the Rocky Mountain foothills.