coming home the famous Wardair 727!
I went in this a few years earlier, on its more normal routing of LGW - Sondrestrom (Greenland) - Vancouver. I wonder if the return flight to Canada the day of your Dubrovnik trip was delayed so they could stick in a quick subcharter. It was for some years a summer regular at Gatwick, and less frequently at Manchester or Prestwick. In the winter it used to live on Vancouver to Honolulu or Acapulco.