The encyclopedia · Engineering & Operations · Operational decision · 1983
Air Canada ran out of fuel mid-air because someone mixed up pounds and kilograms
A brand-new Boeing 767's fuel was measured in kilograms but calculated in pounds. It flamed out at 41,000 feet and glided to a former air base turned racetrack.
Air Canada · Boeing · 1983-07-23
What happened
On July 23, 1983, Air Canada Flight 143, a brand-new Boeing 767, took off from Montreal for Edmonton. The 767 was the airline's first aircraft to measure fuel in metric units — kilograms — but the fuelling paperwork and the conversion the crew used still spoke the old imperial language. With the plane's fuel-quantity gauges faulty, Captain Bob Pearson measured the fuel by hand and converted the reading to kilograms using a density figure that was actually in pounds per litre. The math said the tanks held enough fuel; in reality they held less than half.
Halfway to Edmonton, at 41,000 feet, both engines flamed out. The 767 had become a 60-tonne glider. Pearson, an experienced glider pilot, and First Officer Maurice Quintal flew the dead aircraft toward a former Royal Canadian Air Force base at Gimli, Manitoba — not knowing it had been converted into a dragstrip, with a race meet and families on the runway that day. They brought it down hard but under control, nosing the gear up and skidding to a stop.
Everyone walked away; there were no serious injuries and only minor damage to the plane, which was repaired and flew for another 25 years. The Board of Inquiry blamed Air Canada's procedures, training and manuals, and recommended the airline finish converting its whole fleet to metric — concluding that a fleet mixing the two unit systems was more dangerous than one using either consistently. The aircraft earned a permanent nickname: the Gimli Glider.
Why it happened
- The new metric 767 and the old imperial fuelling documents used different units, and the wrong density figure (pounds per litre instead of kilograms per litre) was applied to the conversion.
- The fuel-quantity gauges were faulty and had been disabled, forcing the crew to measure fuel by hand and trust a manual calculation.
- No independent check caught that the calculated fuel was less than half of what the flight needed.
- Air Canada's fleet was mid-transition between unit systems, and procedures and training had not caught up.
The lesson
Switching unit systems makes every number suspect. One wrong conversion — pounds where kilograms belonged — turned a 'full' tank into an empty one. Standardize the units, then verify the math.
Aftermath
The Gimli Glider became one of aviation's most famous incidents and a textbook case in unit conversion, human factors and the perils of half-finished system changes — a lesson NASA would relearn with the Mars Climate Orbiter sixteen years later. The 767, repaired, stayed in service until 2008. Pearson and Quintal were praised for the landing, though both also took some blame for the fuelling error. The episode is still taught as the canonical example of why a single wrong conversion factor can be catastrophic — and why, when it isn't, it's usually luck and skill.
Sources
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