Southwest flight 4069 was about 9 miles from the airport, over Yukon, Oklahoma, when it descended to the low altitude just after midnight on Wednesday, flight tracking information from FlightRadar24 shows.
"Southwest 4069 low altitude alert," a controller is heard saying in an air traffic control recording by LiveATC.net. "You good out there?"
The pilots' response is not audible.
After the descent stopped, the Boeing 737-800 climbed briefly and then maneuvered for a successful landing at Oklahoma City, tracking data show.
The FAA, in a statement to CNN, said it was investigating the incident, adding: "After an automated warning sounded, an air traffic controller alerted the crew of Southwest Airlines Flight 4069 that the aircraft had descended to a low altitude nine miles away from Will Rogers World Airport in Oklahoma City."
The airlines says it has been in touch with the FAA after the incident.
"Nothing is more important to Southwest than the Safety of our Customers and Employees," the airline said in a statement. "Southwest is following its robust Safety Management System and is in contact with the Federal Aviation Administration to understand and address any irregularities with the aircraft's approach to the airport."
This marks the second recent incident involving a Southwest flight narrowly missing the ground. In April, the crew of Southwest Flight 2786 aborted its approach into Lihue Airport on the island of Kauai but descended to 400 feet above the Pacific Ocean instead of climbing.
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