Virgin Atlantic VS23 from London Heathrow to Los Angeles was forced to return to LHR after the pilots noticed severe vibrations in engine number 2, the pilots declared an emergency above Scotland.
At 15:41 (UTC +0) the Boeing 787-9 Dreamliner took off runway 27L, 50 minutes into the flight G-VWHO returned to London Heathrow. At 17:46 (after 2 hours of flight) the aircraft touched down again on runway 27L and cleared the runway shortly after. 
First sight of Virgin Atlantic #VS23 (G-VWHO) crossing over 27R at 8000ft after declaring an emergency. pic.twitter.com/cvnHgBDDJ1 — Ket ? (@OnTheRoadToYou) September 28, 2017
#VS23 to Los Angeles declared an emergency and turned back to Heathrow shortly after passing Glasgow. Cause not yet known. — Flight Alerts ? (@FlightAlerts777) September 28, 2017
#VS23(G-VWHO) Landed #27L @AirportWebcams @flightradar24 @FlightBreaking @FlightEmergency @airlivenet contacted fire services pic.twitter.com/WsVgFs8DTx — Never You Mind (@lhrgeek) September 28, 2017