Pprune-- a good reply, but Concorde is one of those old aircraft, which still carries a Flight engineer and calling him a 3rd crew member will really get them annoyed. In fact when Concorde first went into service the pilot's licence was stamped as " Only valid if accompanied by a valid Flight Engineer"
Navigation is by good old fashioned triple INS, which can be updated once the aircraft is in range of a VOR/DME site.
Yes the electronic system are American, but as the old saying goes " Its not the equipment you got, but what you do with it that counts"
regards Brit312