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In page John Denver:

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In addition to Denver's failing to refuel and his subsequent loss of control while attempting to switch fuel tanks, the NTSB determined other key factors that led to the crash. Foremost among these was his inadequate transition training on this type of aircraft and the builder's decision to put the fuel selector handle in a hard-to-reach place.[1][9] The board issued recommendations on the requirement and enforcement of mandatory training standards for pilots operating home-built aircraft. It also emphasized the importance of mandatory ease of access to all controls, including fuel selectors and fuel gauges, in all aircraft.[citation needed]