The jet slowed to landing speeds and dipped lower than 500 feet above the ground near the old Super Saver in Yukon, about nine miles northwest of Will Rogers World Airport. It was expected to approach for landing from the north, according to the flight tracking company Flightaware.

The unusual descent triggered the “Minimum Safe Altitude Warning,” which alerts controllers if an aircraft gets too low. Here’s the tower at Will Rogers radioing the pilots:

“Southwest 4069, uh, low altitude alert,” the tower at Will Rogers radioed to the pilots at 12:06 a.m., per liveATC’s air traffic archives. “You good out there?”

The aircraft quickly rose, looped around and landed safely at the airport.

“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,” a Southwest spokesperson wrote in an email on Friday.

The FAA said it’s investigating the incident.