Before last month’s crash of a flight that began in Ethiopia, Boeing Co. said in a legal document that large, upgraded 737s “cannot be used at what are referred to as ‘high/hot’ airports." At an elevation of 7,657 feet -- or more than a mile high -- Addis Ababa’s Bole International Airport falls into that category. High elevations require longer runways and faster speeds for takeoff. The Ethiopian airport’s altitude hasn’t been cited as a factor in the downing of Flight 302 and likely didn’t cause the crash. But it could have exacerbated the situation because an airplane’s performance degrades...