Air Canada's Boeing 767 was the first metric aircraft in a fleet that otherwise counted its fuel in pounds, and on 23 July 1983 that difference emptied its tanks at 41,000 ft. A fault in the fuel-quantity system meant the load had to be confirmed by dripsticks, in centimetres, then converted through litres to kilograms. For the last step the ground and flight crews used 1.77 — the factor that turns litres into pounds, not the roughly 0.8 that gives kilograms. The figure looked like kilograms to everyone who read it, and it was about 2.2 times too large, so the aircraft left Montreal, and again Ottawa, with close to half the fuel the crew believed was aboard.
The bridge this section warns about, volume to mass through the day's real density, had been crossed with the wrong constant, twice. Over Red Lake, halfway to Edmonton, the low-pressure warnings began; both engines flamed out by 35,000 ft, and the electrical loss stripped the glass cockpit to a handful of standby instruments. The captain, a glider pilot, sideslipped the powerless 767 onto a disused runway at Gimli, stopping short of the people camped beyond its end. Sixty-nine aboard, no fatalities, no serious injuries — a landing, not a crash, and the reason the aircraft is remembered by the airfield's name.
The inquiry named the density error among a chain of corporate causes: a mixed metric and imperial fleet, no one clearly assigned to calculate the fuel, confusion over the minimum-equipment status that made the dispatch itself illegal. What changed attacked the arithmetic directly — dripstick charts redrawn to read straight to kilograms so the density multiplication vanishes, the misleading term specific gravity struck from the fuel slip, and the fuel figure made a cross-checked calculation by maintenance and crew independently. The conversion in this section is the one that has to be right first: the limits and the endurance are written in kilograms, and the bowser only ever delivers litres.