Preflight checklists, which are standard operating procedures for all pilots today, were not used prior to 1935. Boeing developed the B-17 bomber which was flown during WWII to challenge other military contractors.

On the inaugural flight of the B-17 in 1935, the plane crashed at Wright Field in Dayton, Ohio when the Captain left the elevator lock on. The crash resulted in the death of the two pilots.

A subsequent Boeing think tank session determined that the crash could have been avoided if there had been a preflight checklist. Aircraft were becoming too complex for pilots to memorize all check items. Hence the first checklist was born.

Today, failure to correctly conduct a preflight check using a checklist is a major contributing factor to aircraft accidents.