United A320 and United A320 at Houston on May 8th 2014, near collision on initial climbs

A United Airbus A320-200, registration N481UA performing flight UA-437 from Houston,TX (USA) to Mexico City (Mexico), was cleared to turn left heading 135 and takeoff from runway 15L at about 21:45L (02:45Z May 9th).

A United Airbus A320-200, registration N435UA performing flight UA-601 from Houston,TX (USA) to Vancouver,BC (Canada), was cleared to turn right heading 340 and takeoff from runway 09 about one minute after UA-437 received takeoff clearance.

About one minute after UA-601 received takeoff clearance the controller inquired "what's your heading now?" and instructed "stop your turn" and restricted UA-437 to 3000 feet.

Both aircraft reported a TCAS resolution advisory, UA-437 received a climb resolution advisory and climbed above 3000 feet levelling off at 4000 feet, UA-601 received a TCAS descend resolution advisory and descended until clear of conflict.

About 10 minutes after the occurrence, both crew on departure frequency, a quick discussion occurred between the two crews, UA-437 inquiring with UA-601 whether they knew what had happened, it appeared UA-437 was exactly over UA-601. The departure controller said, he suspected one of the aircraft received a wrong turn, the departure out of 09 probably should have received a left instead of a right hand turn.

Both aircraft subsequently continued to their destinations for safe landings.

The FAA reported the minimum separation between the two aircraft reduced to 400 feet vertical with no lateral separation.

Map (Graphics: AVH/Google Earth):