By the seat of their pants
Canada went fully metric in the late 1970s after a phase-in process that started in 1971. But it still had its fair share of hiccups over confusion about metric versus imperial units, including a 1983 Air Canada flight running out of fuel. Air Canada had been measuring fuel in pounds for years before finally switching to kilograms.
The Boeing 767 jet, Canada's first aircraft using metric measurements, had been filled with too little fuel on that particular day. The flight, scheduled to travel from Ottawa to Edmonton, had to make an emergency landing in Gimli, Manitoba.
To make matters worse, the flaps on the plane couldn't be engaged due to the engine failure, forcing the pilots to land at a much faster speed than they should have. The New York Times explained at the time: "The entire episode produced two contradictory emotions in the aviation world. One was deep concern over how simple errors, this time in a switch to the metric system with the introduction of the Boeing 767, could come so close to producing a major disaster. The other was admiration at the skill of the pilots, whatever their role in the original errors, in putting the huge wide-body craft down safely when, without power, they would have no chance to make second landing approach."
