FAA investigating close encounter at Minneapolis-St. Paul International Airport

Federal aviation authorities are investigating a close encounter between an airliner attempting to land and another poised to take off Wednesday evening at Minneapolis-St. Paul International Airport.

The incident involved an American Airlines flight arriving from Dallas shortly before 6:30 p.m. and a Delta Air Lines jet on the runway and cleared for departure to Santa Ana, Calif., the Federal Aviation Administration (FAA) said Thursday.

"The American Boeing 737 was approaching to land just as an air traffic controller cleared the Delta Airbus A220 for an immediate takeoff," the FAA said.

"After the controller told the American flight to go around, the aircraft passed above and to the left side of the Delta flight."

The FAA said it was investigating "the closest proximity between the two aircraft."

Depending on its findings, the agency could deem the incident to be as serious as a "collision being narrowly avoided" to something as minor as a vehicle, person or aircraft improperly positioned in "a protected area ... but with no immediate safety consequences."

Evan Heath, who works as a ramp leader for United Airlines, said he watched the two aircraft draw closer and feared the worst.

"I thought, 'Oh my god, they're going to collide,'" Heath told the Star Tribune. "I see the American [jet] just flying at a low altitude, and he kept going straight. Normally, they make a left bank."

In his seven years working at the airport, Heath said, "I've never seen this happen."

The American flight landed about 20 minutes later, according to FlightAware, an aviation tracking website.

The Delta airliner left its Terminal 1 gate about 4 minutes ahead of schedule, airlines spokesman Morgan Durrant said.