DENVER -- The CALL7 Investigators have confirmed the FAA is investigating a Nov. 23rd incident where two passenger jets nearly collided in the airspace over Colorado.

Sources told CALL7 Investigator John Ferrugia the two planes merged on Air Traffic Control radar at the same altitude and in the same moment.

Said one source, "They were within a blink of an eye of colliding," and "It was the ugliest thing I've ever seen in all my years."

A spokesman for the FAA, Mike Fergus, told 7NEWS, "Alarms went off," in the Denver Air Route Traffic Control Center, also known as the Longmont center.

The incident is classified as an "operational error" which, Fergus explained, is typically a mistake made by an air traffic controller.

It happened around 7 a.m. on the Monday before Thanksgiving, when airline traffic was beginning to increase for the upcoming holiday.

Several planes were en route to Denver on an arrival path from the northeast, called "Sayge Six."

Sayge is described to 7NEWS as a "highway in the sky" with traffic only allowed to travel in one direction, toward DIA, at 19,000 feet and 250 knots for jets.

The Sayge marker is about 47 miles northeast of DIA, and is an air traffic control handoff point between Longmont Center and DIA Approach Control.

Sources told Ferrugia that on Nov. 23, air traffic was very busy over Colorado and Republic Flight No. 1539 was vectored on a route toward DIA that was south of the Sayge "highway" and running parallel to other air traffic.

Republic Flight 1539 had already passed the Sayge marker when an air traffic controller in the Longmont center told the pilots to "proceed to Sayge," apparently thinking the pilots would simply merge with the traffic already on the "highway," sources said.

7NEWS was told the Republic captain questioned the controller's command, which was repeated.

The pilots then turned about 180 degrees toward the Sayge marker and were traveling in the wrong direction on the "highway," explained the sources.

Inbound to DIA on the "highway" was SkyWest Flight No. 6764.

Fergus told 7NEWS alarms sounded in at least one of the cockpits telling the pilots to take evasive action.

One plane dove while the other was ordered to pull up, and the two missed by about 200 vertical feet, sources said. The source could not confirm the horizontal separation of the two planes because the radar images briefly merged into a single image.

Following behind the SkyWest flight, and also inbound on the Sayge arrival, was Frontier Airlines Flight 615, which also "lost separation" with the Republic jet, however, sources said the danger was not immediate.

The FAA has confirmed many of the details of the incident and is investigating, but Fergus wanted to emphasize that even though there appears to have been an error in air traffic control, the backup emergency systems onboard the aircraft worked properly and alerted the pilots who succeeded in safely separating the aircraft.

No one is believed to have been hurt in the incident.

Fergus explained that incidents are categorized by the FAA as A, B, C, or D level with "A" incidents being the most critical.

He said this particular "operational error" was classified as "B."