Boris III of Bulgaria
In 1926, Baur became a pilot of Deutsche Luft Hansa. In the same year, he also became a member of the NSDAP (Nazi Party No. 48,113). On 1 April 1931, he flew the opening flight of the Berlin-Munich-Rome route, known as the Alpine flight, whose passengers included Nuntius Eugenio Pacelli, Arturo Toscanini and Tsar Boris III of Bulgaria.