Guynemer failed to return from a combat mission on 11 September 1917. The previous week had been one of mechanical ills, in both his assigned aircraft and the ones he borrowed. At 08:30, with rookie pilot Jean Bozon-Verduraz, Guynemer took off in his Spad XIII S.504 n°2. His mission was to patrol the Langemark area. At 09:25, near Poelkapelle, Guynemer sighted a lone Rumpler, a German observation plane, and dove toward it. Bozon-Verduraz saw several Fokkers above him, and by the time he had shaken them off, his leader was nowhere in sight, so he returned alone. Guynemer never came back.