On the morning of 30 October 1935, the Boeing Model 299—prototype of what would become the B-17 Flying Fortress—roared down the runway at Wright Field, Ohio. At 300 feet it stalled, winged over, and crashed in a fireball before the assembled brass of the Army Air Corps. Major Ployer Peter Hill, the pilot, died of his injuries. Boeing's gamble seemed lost.

The investigation found no structural flaw, no engine failure, no design defect. The elevator control surface had been locked by a gust lock—a simple pin meant to secure the tail on the ground—and neither Hill nor his copilot had released it before takeoff. The Model 299 was not too much airplane for one man; it was too complex for any one man's memory.

The Air Corps did not cancel the program. Instead, its pilots and engineers sat down and wrote out every step that mattered: takeoff, flight, before landing, after landing. They created the pilot's checklist. With it, the twelve evaluation aircraft that followed flew 1.8 million miles without a serious accident. The Army accepted the bomber, and eventually ordered 12,731 of them. From that day to this, no pilot of a complex aircraft has flown without a silent copilot on paper. The checklist was born in fire, but it has saved more lives than any single invention in aviation.