Complex sentence: She was the first woman to gain a pilot license in the United States when, in 1911 she earned the first U.S. pilot's certificate issued to a woman by the Aero Club of America.
Split into simpler sentences: She was the first woman to gain a pilot license in the United States. In 1911 she earned the first U.S. pilot's certificate issued to a woman by the Aero Club of America.