PHILADELPHIA could be the headquarters of what is likely to be called Virgin USA. ABTN does not go in for airline rumours (two a penny) but prefers to rely on facts but in this case there is little doubt that the city of the Liberty Bell, 70 miles south west of New York, is among the front runners for the new airline in which Sir Richard Branson is an investor. New York is still the favourite for the Virgin base, a city, unlike Philadelphia, served from the UK. San Francisco; Washington, DC; Boston and Los Angeles have also been suggested.