About eight minutes after Biden's flight landed at 9:28 a.m. Monday, a departing plane and an arriving plane came dangerously close to each other at 9:36 a.m.
The two planes may have passed within 300 feet apart vertically and about 400 feet apart horizontally, aviation sources told ABC News, citing preliminary calculations that were subject to change.
"A Jetlink flight was cleared to takeoff from O'Hare Airport's runway 32L while a Skywest flight was descending to land on runway 9R," the FAA said in a written statement. "As the Skywest aircraft was coming in, a controller instructed the Skywest flight to perform a go-around procedure. The Skywest plane passed behind and above the departing Jetlink flight. The FAA will review the event to see if any additional training or procedural changes might be necessary."
The departing pilot -- carrying a full load of 50 passengers -- saw the arriving flight overhead and decided to delay the plane's pull-up until it was further down the runway, according to aviation sources, ultimately taking off at around 9:37 a.m.
By that time, the overhead plane, a United Express SkyWest flight with 29 people aboard, already had been told to circle the airport to delay its landing, sources said. It ultimately landed at 9:52 a.m.
FAA: Biden Arrival Not Involved
The FAA said Biden's plane or the logistics of its arrival had no role in the close call. They added that Biden was never in danger.
The Chicago Tribune reported that an automated spacing-detection monitor in the control tower sounded an alert that the two planes had violated separation standards.
The FAA has not yet confirmed that report to ABCNews.com.