Boeing B-17 Flying Fortress Model 299

The Model 299 was Boeing's prototype for a 1934 US Army Air Corps requirement for a bomber able to carry 910 kg of bombs 3,200 km at 320 km/h. It first flew on 28 July 1935 and set a 406 km/h speed record on its ferry flight to Wright Field. It crashed during a demonstration because of a flight-crew error (the control-surface gust locks were left engaged), not a technical fault — the episode led directly to the mandatory pre-flight checklist still used across aviation today. Despite the crash and its higher unit cost, the aircraft impressed Army Air Corps leadership enough to win a development contract. The unofficial nickname "XB-17" became common later, but was never an official military designation.