Timing is everything! Lufthansa A340 flies over an Embraer 145. Some may see this and be shocked that this goes on but rest assured, this is completely normal and both aircraft are TCAS equipped (Terminal Collision Avoidance System). TCAS is a screen in the cockpit that shows other airplanes that are within the subject aircraft's airspace. The TCAS picks up other airplanes via their transponder which every airliner has on board. In addition to TCAS, ATC is also monitoring traffic, which is especially heavy over central Europe
