Details on the emergency landing at Heathrow are scarce at this moment but it is believed the United Airlines flight took off from the London airport at 12:23 this afternoon.
The plane was heading to San Francisco and flight tracking data shows it got near Milton Keynes before turning back.
Reports say the Boeing 777-200 aircraft stopped climbing at 15,000 feet before returning.
The crew reportedly declared an emergency and made a U-turn to request an immediate return to Heathrow due to a technical issue.
According to AirLive, the same aircraft declared an emergency on approach to San Franciso due to an engine issue.