It was viable in that it broke even on its running costs, but towards the end it wouldn't have covered the cost of actually acquiring the aircraft, nor any major expenditures such as upgrades required for safety or compatibility with newer systems.

Concorde used to serve a lot more than just the NYC-London/Paris route. It used to serve Bahrain, Rio de Janeiro, Dakar, Caracas, Washington DC, Miami, and Mexico City. Those faded away due to a lack of demand. (Ignoring Dallas and Singapore, as those failed due to restrictions on supersonic flight.)

I'm sure a new design could be a lot more economical. Of course, regular airliners have become a lot more economical as well, so it's a tougher bar to clear.

  Concorde was more-or-less viable for BA (though not for AF). 

Can you elaborate, or direct me to a source?

I'm genuinly interested.

There was an extended forum thread (on pretty much all aspects of Concorde - went on for tens or hundreds of pages) that was linked from here once - afraid I don't have it to hand.

If this thread is anywhere, I would bet its on flyertalk (awesome air travel forum with great info).

Maybe this one: http://www.pprune.org/tech-log/423988-concorde-question.html

Very interesting.

Thank you very much.