Complex sentence: The Air Corps Act of 1926 required that 90% of all Air Corps officers be rated, and that for reasons of economy, by 1929 at least 20% of tactical pilots had to be enlisted men.
Split into simpler sentences: The Air Corps Act of 1926 required that 90% of all Air Corps officers were required to have a rating. Also for reasons of economy, the Act required that by 1929 at least 20% of tactical pilots be enlisted men.