With a weakening balance sheet, TWA would sell its Heathrow rights to American for $425 million shortly after this schedule was published. Its chief rival, Pan Am also sold its Heathrow routes off, to United. Heathrow routes were the most profitable in the system and cost the airline $500 million per year in lost revenue. Heathrow would cause TWA to retreat to Gatwick with flights only to St. Louis. Internationally, Istanbul, Berlin, and Stockholm came on line.