A United Boeing 777-200 has declared an emergency after takeoff from London Heathrow.
United Airlines flight UA949 departed London Heathrow at 12:23 BST from runway 27L. The Boeing 777-200ER (registration N229UA) stopped the climb at 15,000 feet before turning around.
The crew declared an emergency (squawk 7700) as the flight to San Francisco made a U-turn to request an immediate return to London Heathrow due to a technical issue.
Seven days ago, the same aircraft declared an emergency on approach to San Francisco due to engine number 2 issue.
UPDATE 13:15 BST
United flight UA949 landed on runway 27R.
UPDATE 13:18 BST
The Boeing vacated the runway and stopped on the taxiway while emergency vehicles met the aircraft.
UPDATE 13:20 BST
The plane is escorted to the gate by 3 fire trucks to terminal 2.

UPDATE 13:23 BST
The airline is confirming to AIRLIVE the maintenance team needs to evaluate a technical issue on the plane before a new departure.
UPDATE 13:36 BST
The Boeing 777-200 is now parked on remote stand of the airport to check cause of smoke in the cabin.
UPDATE 14:00 BST
The flight is canceled to take the plane out of service “to address a technical issue”.
