PHOENIX -- The 911 call has now been released following the deadly midair collision near Carefree Highway and New River Road last month.
Four people were killed May 31 when two single-engine planes collided after accidentally turning toward each other at the same time.
"I just saw two what looked like ultralights, spiraling down," said the witness who called 911. "One looks like it's on the ground upright. The other, I think, it's in flames."
A National Transportation Safety Board preliminary report says radar data indicates that the planes were about a mile apart before the collision, both flying northerly at about 900 feet above ground level.
NTSB investigator Van McKenny says the planes were flying in uncontrolled airspace where separation of aircraft is the responsibility of pilots.
Two of the victims killed were part of a local hot air balloon company. The other two were flight instructors from an aviation school.
Hot Air Expeditions announced that its president, Margie Long, and project manager, Carl Prince, were aboard a training flight that collided with a TransPac Aviation Academy plane
The other two victims were flight instructors for TransPac. Paul Brownell, 37, had been a top instructor since 2005. Basil Onuferko, 26, had just started with the company and was up with Brownell on a training flight before being scheduled to take his first student the following day.