On October 30, 1935, the Boeing Model 299—prototype of the B-17 Flying Fortress—took off from Wright Field, Ohio. At 300 feet, it stalled, winged over, and crashed in flames. Two men died, including Boeing chief test pilot Leslie Tower. The investigation found nothing wrong with the aircraft. The problem was human: the crew had forgotten to release the gust lock on the elevator. The Model 299 was so complex that even experienced pilots couldn’t rely on memory alone. The Army Air Corps responded with a radical idea: a written checklist for takeoff, flight, and landing. That simple protocol—now universal in aviation—was born from tragedy and saved countless lives.