Well, from my understanding of TCAS, depending on the current air situation, both transponders converse on an appropriate course of action and that is then relayed to the pilots via the TCAS. First a TA, Traffic Alert and finally an RA, Resolution Advisory if needs be. In this case both aircraft were in level flight so I guess a compromise would have been reached between both Transponders maybe taking into account the speed of both aircraft and the wind speed and direction. Generally time to impact is the deciding factor on when a TA and RA are given. Headings don't directly influence whether or not an aircraft should climb or descend.
The one question I'd like to ask is this......Would it not be a good idea if the on-board computer automatically engages a climb or descent on receipt of an RA? Would this not take out the possibility of human error, ie whether to follow TCAS or ATC. If an RA is given the autopilot should override any human induced climb or descent until such time the conflict has resolved. Obviously, the TCAS would take into consideration other aircraft. But that should be no different to the way TCAS works now. At least then, I think the possibility of something like Lake Constance happening again would almost virtually be unthinkable. Humans are very prone to suggestion. This means that only a slight suggestion will impact your decision process. ie will I follow my TCAS or do what ATC told me. I think it just might work.
Any comments.....??
By the way the program was top class. Well done to the BBC.