The Federal Aviation Administration (FAA) is investigating a Southwest Airlines flight on June 20 that received an air traffic control alert about its extremely low descent around 9 miles before its runway landing at Will Rogers World Airport in Oklahoma City.

Flight 4069 dropped to around 500 feet above the nearby city of Yukon sometime after midnight. According to ABC News, a Minimum Safe Altitude Warning system alert at 12:05 a.m. is what envoked an air traffic controller to check in with Flight 4069’s pilot.

In an audio archive provided by LiveATC.net, the controller is heard speaking to the pilot. In the audio, he says, “Southwest 4069 low altitude alert. You good out there?”

The response is inaudible, but USA Today shared that the pilot “quickly regained altitude” and ultimately landed at Will Rogers World Airport.

The plane was a Boeing 737-800 that left from Las Vegas.

What Else Should I Know About Southwest Airlines Flight 4069?

In a brief statement, the airline addressed what occurred by saying, “Nothing is more important to Southwest than the Safety of our Customers and Employees.”

“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,” the carrier added.

Earlier this month, news broke that the FAA was investigating an April Southwest flight that dropped just above the ocean at “an abnormally high rate of more than 4,000 feet per minute.” That flight was also a Boeing 737. Sources for that flight, Flight 2786, and Flight 4069, haven’t stated whether the individual trips were commercial flights with passengers.

On June 18, Southwest celebrated its 53rd birthday by offering airline tickets as low as $53. People reported that the special ticket pricing was scheduled to end on June 20.