Air Canada Flight One Forty-Three, the Gimli Glider, and the Metric Conversion That Turned a Boeing Seven Sixty-Seven into a Glider Over Manitoba

On July 23, 1983, Air Canada Flight 143 - a Boeing 767 carrying 61 passengers and 8 crew members - became a glider at 41,000 feet over northwestern Ontario because a fuel quantity had been calculated in the wrong units. The error produced fuel figures 2.2 times larger than what was actually on board. Sixty-nine people survived. The aircraft flew for Air Canada for another 25 years, and was never called anything but the Gimli Glider.

What Caused the Gimli Glider Accident?

The cause was a single embedded unit error: pounds per liter used in place of kilograms per liter when converting fuel quantity. Canada had officially adopted the metric system in 1976, and aviation fuel was being calculated in liters and kilograms. The density factor applied during refueling was 1.77 pounds per liter - the imperial conversion - rather than 0.803 kilograms per liter.

Because 1 kilogram equals 2.2 pounds, every fuel figure the crew received was inflated by a factor of 2.2. The error was internally consistent throughout the entire calculation chain. It produced plausible-looking results at every step.

Why the Faulty Fuel Calculation Went Undetected

The aircraft’s Fuel Quantity Indication System (FQIS) - a fully digital, computer-driven fuel monitor, still a relatively novel system on a newly delivered aircraft type - was inoperative that morning. The Minimum Equipment List (MEL) permitted dispatch with the FQIS inoperative, provided the crew verified fuel manually using a drip stick.

A drip stick is a calibrated rod inserted into the fuel tank access port on the underside of the wing. It measures the fuel level in centimeters, which is then converted to liters, then to kilograms. The conversion from liters to kilograms was the step where the wrong density factor was applied - and the MEL authorization for FQIS dispatch did not adequately account for the complexity and error potential of that manual alternative.

Several crew and ground personnel encountered arithmetic that didn’t quite add up during the fueling process. They rechecked their math - but within the same flawed framework. The unit assumption was never questioned. That is the most dangerous kind of error: the kind that looks right all the way down the chain.

The Fuel Numbers That Doomed Flight 143

Flight 143 departed Montreal-Dorval Airport and stopped at Ottawa before continuing to Edmonton. At departure from Montreal, the calculated fuel load was approximately 22,300 kilograms. The actual fuel on board was closer to 10,000 kilograms.

At Ottawa, additional passengers boarded and more fuel was ordered. The same conversion error ran through every new calculation. When the flight departed Ottawa, the crew believed they had approximately 22,300 kilograms of usable fuel. The actual usable fuel was approximately 9,000 kilograms. The flight required roughly 22,000 kilograms to reach Edmonton.

They had less than half of what they needed.

When Both Engines Quit at 41,000 Feet

Forty-six minutes after departing Ottawa, a crew oxygen warning activated, followed by low fuel pressure on the left engine. The left engine flamed out. The crew began diverting. Then the right engine quit.

When a 767 loses all engine power, most electrical and hydraulic systems go offline. The RAM Air Turbine (RAT) deploys automatically from the belly of the aircraft - a small propeller driven by airflow that generates just enough power for a minimal instrument set and limited flight control authority. No flaps beyond ten degrees. No spoilers. No slats. Limited braking. No go-around capability.

One approach. One shot.

Captain Bob Pearson had nearly 23,000 hours in his logbook. First Officer Maurice Quintal had been stationed at RCAF Station Gimli, Manitoba, earlier in his career with the Royal Canadian Air Force. He knew the runways were long. He calculated the distance and suggested Gimli.

Landing an Unpowered 767 on a Racetrack

What Quintal didn’t know was that RCAF Station Gimli had been decommissioned. Part of the old facility, including a portion of the main runway, had been converted into the Gimli Motorsport Park. On July 23, 1983, it was race day. There were spectators on the runway - families, children on bicycles.

The aircraft came in high. Too high. Without full flaps or functioning spoilers, Pearson was carrying excess altitude and airspeed with no ability to add energy if he got slow. The approach was heading toward an overshoot.

He did something that is not in the 767 flight manual: he put the aircraft in a forward slip.

Pearson had flown gliders. The forward slip - cross-controls, bank the nose off the flight path, increase drag, bleed altitude without gaining airspeed - is a standard technique in light aircraft training. He applied it to a two-hundred-thousand-pound wide-body, and it worked.

The main gear touched down on the concrete. The nose gear, without hydraulic pressure to lock it down, collapsed on contact. The nose scraped along the runway. The aircraft stopped 368 feet from the end of the runway.

Outcome and Investigation

Ten people were treated for minor injuries - several from the emergency evacuation, including passengers who jumped from rear exits before slides deployed fully. A small number of bystanders near the aircraft sustained minor burns from fuel vapors. There were no fatalities.

Sixty-nine people walked away from a Boeing 767 that had glided more than 60 nautical miles without engine power and landed, unpowered, on a decommissioned military runway being used as a racetrack.

The Transportation Safety Board of Canada found multiple systemic failures underlying the unit error: drip stick conversion procedures lacked clear standardization for personnel navigating Canada’s metric transition, the FQIS MEL dispatch authorization didn’t adequately account for the error potential in the manual alternative, and no mandatory independent cross-check existed in the refueling verification chain.

Captain Pearson received the Fédération Aéronautique Internationale’s award for extraordinary airmanship. First Officer Quintal was also recognized.

The aircraft, registration C-GAUN, was repaired and returned to service. Air Canada flew her for another 25 years. She was retired in 2008. She never lost the name Gimli Glider.

Why This Still Matters to Every Pilot

The Gimli Glider was not caused by mechanical failure, weather, or a communications breakdown. It was caused by an assumed unit that everyone touched and nobody verified - and because the same wrong assumption ran through every calculation, the numbers looked right at every step.

In general aviation, the parallel risk takes a different form. Fuel gauges in certified light aircraft are required by regulation to read accurately only at empty. Everything above zero is guidance, not a guarantee. The only fuel reading a certificated gauge is legally required to get right is the one that means you’re already out of options.

Verify fuel visually. Run the math. Use elapsed time and fuel flow against your planned values. If something doesn’t add up, ask the question before you push the throttle - not at 41,000 feet when the answer no longer matters.

Key Takeaways

Air Canada Flight 143 lost both engines on July 23, 1983, because fuel was calculated using a pounds-per-liter density factor (1.77 lbs/L) instead of kilograms-per-liter (0.803 kg/L), producing fuel figures 2.2 times higher than what was actually loaded.
The inoperative FQIS required a manual drip stick verification - but the MEL authorization for that dispatch did not include adequate safeguards against the error potential in the manual calculation procedure.
The error survived multiple rechecks because it was internally consistent: every person who questioned the numbers resolved the discrepancy by rechecking arithmetic within the same flawed unit framework.
Captain Pearson used a forward slip - a light aircraft technique not in the 767 manual - to land an unpowered wide-body on a decommissioned runway being used as a racetrack, stopping 368 feet from the end.
Fuel is the only resource in flight that cannot be troubleshot or negotiated with in the air. Visual verification, independent cross-checks, and unit confirmation are not redundant steps - they are the only protection against an error that looks correct all the way down the chain.