The dangers of more powerful positive lightning were not understood until the destruction of a glider in 1999 . It has since been suggested that positive lightning might have caused the crash of Pan Am Flight 214 in 1963 . At that time , aircraft were not designed to withstand such strikes because their existence was unknown . The 1985 standard in force in the US at the time of the glider crash , Advisory Circular AC 20-53A , was replaced by Advisory Circular AC 20-53B in 2006 . However , it is unclear whether adequate protection against positive lightning was incorporated
Flight 214
Pan Am Flight 214
Aviation safety