I have American friends coming over next year to spend a week with me befopre flying on to Germany. They live in Texas so it's easy to get them to arrange a flight from Houston to Newark and then onto Bristol (so I can meet them) I can also get them back to Bristol airport for them to catch a flight to Bremen, Hamburg, Berlin, or Frankfurt (whichever is easiest/nesrest to their destination). Will either of these four airports be able to fly them directly back to the States? probably via Newark rather than have to fly back to the UK and change planes at Gatwick or Heathrow?
I've just done a quick search (by no means exhaustive) and it would appear that only Frankfurt does direct flights to US. All others show changes in London, Paris or Amsterdam.
Lufthansa fly directly from Frankfurt to Houston, with a 10 hour 30 minute flight time. (Flight no LH440). The same flight also appears in the schedules of United Airlines, under a code share arrangement. (Flight no UA8866)