Menckhoff was in his 30's when the war began making him one of the oldest pilots in the German Air Service. On September 23, 1917, he was shot down while trying to assistWerner Voss in his famous dogfight with 56 Squadron. He and Voss were both shot down by Arthur Rhys Davids. Five days later, Menckhoff was shot down again by 56 Squadron. Finally, on July 25, 1918, Menckhoff was shot down near Chateau Thierry by Lt. Walter Avery, an American with the 95th Pursuit Squadron, and Menckhoff was captured. In August 1919, he escaped from Camp Montoire, made his way to Switzerland and remained there until his death in 1948.