Saturday night, the Federal Aviation Administration is pointing to a faulty headset that an air traffic controller was using.
A passenger peaked out the window, and saw another plane just below. This happened in Detroit Friday night.
A delta 737 from Phoenix and a small regional jet approach the runway from different directions and at different altitudes.
They passed within two miles of each other, well within the three-mile safety zone that jets usually fly.
The FAA says the confusion came when an air traffic controller's headset began to give out, broadcasting intermittently with the pilots unable to hear all the instructions.
"Obviously that's not a desirable situation and perhaps even more insidious is the fact the pilot may not know what he or she isn't hearing," said Steve Wallace, former FAA director of accident investigation.
The FAA says there was no threat of a collision because both pilots could see each other's planes - and both planes landed safely.
But this latest incident comes just three days after another scare in the skies - when three planes nearly collided over the nation's capital.
It happened when a commuter airliner took off in the wrong direction from Reagan Airport, heading into the path of a second jet cleared to land on the same runway.
An alert air traffic controller saw the confusion and ordered the landing pilot to change course.
"I would take away the fact the system worked," Wallace said. "I am never one to say that passengers need to worry about anything in this system when we carry almost a billion people a year safely."
ABC's safety expert says it's been 34 years since we've had a mid-air collision on US airliners.