Federal officials are investigating an incident in which two United Airlines planes may have flown too near to each other over Houston.

A spokesman for the Federal Aviation Administration said Friday that the two jets came within less than a mile of each other and 400 feet apart in height on May 9. Both planes had just taken off from Bush Intercontinental Airport.

The FAA says an air traffic controller told the pilot of United Flight 601 to turn right after takeoff, then noticed that the plane was heading into airspace normally reserved for planes on another runway. United Flight 437 had just taken off from that second runway.

The FAA says the controller gave both pilots instructions to keep the planes apart.

United isn’t commenting yet.

(AP)