The Gimli Glider: How a Kilograms-to-Pounds Mix-Up Nearly Crashed a Boeing 767

What Happened on Air Canada Flight 143?

Air Canada Flight 143 was a scheduled passenger flight from Montreal to Edmonton, with a brief stopover in Ottawa. The aircraft carrying the route was a brand-new Boeing 767-200, one of the most sophisticated commercial airliners of its era.

While cruising at 41,000 feet over Red Lake, Ontario, a warning alarm sounded in the cockpit. The fuel pump warning light indicated a fuel pressure issue. Within minutes, the left engine flamed out, followed quickly by the right engine.

The plane was completely powerless. All electronic instruments flickered off, leaving only battery-powered analog backups. The pilots had to glide a 132-ton jetliner with no thrust and minimal controls.

Fortunately, Captain Bob Pearson was an experienced glider pilot, and First Officer Maurice Quintal had served at Gimli, a former Royal Canadian Air Force base. With superb airmanship, the crew side-slipped the airliner to lose altitude quickly and landed on Gimli's decommissioned runway, which had been converted into a local sports car and drag-racing track.

The Real Cause — A Kilograms/Pounds Mismatch

During the investigation, the Canadian Aviation Safety Board uncovered a series of human factor errors that started with a metrication program.

Canada was in the middle of converting from the imperial system to the metric system. The new Boeing 767 was Air Canada's first aircraft to use metric calibrations, expecting all fuel measurements, gauges, and calculations to be processed in kilograms instead of pounds.

Due to a mechanical failure in the plane's Fuel Quantity Indicator System (FQIS), ground crew used manual drip sticks to verify the fuel volume in liters. To convert the liters of fuel to weight, they needed a density multiplier.

The ground crew used 1.77 as the density multiplier. However, 1.77 represents the density of Jet A-1 fuel in pounds per liter (lb/L). The correct density factor in metric was 0.803 kilograms per liter (kg/L).

Because they multiplied by 1.77, the crew loaded only 10,115 kilograms of fuel instead of the required 22,300 kilograms, believing they had met the safety margins. In reality, they had loaded 22,300 pounds of fuel — less than half of what they needed to reach Edmonton.

How Big Was the Shortfall, in Real Terms?

The difference between kilograms and pounds represents a multiplier of 2.2046. Because of this ratio, the aircraft took off with a massive deficit of 12,185 kilograms of fuel. The engines starved of fuel roughly halfway through the flight.

Why This Still Matters Today

The Gimli Glider stands alongside the Mars Climate Orbiter as one of the most famous safety case studies in aviation history. It shows how software calibration upgrades and physical operational checks must be unified under consistent measurement frameworks.

In international aviation and maritime logistics, fuel weight, cargo capacity, and passenger payloads are continually calculated across regions using different units. Standardizing double-check procedures and validating conversions is essential to human and system safety.

To avoid making similar errors in your own calculations—whether in drafting, hobby projects, or metrics calculations—always use direct formulas, test conversion endpoints, and avoid intermediate rounding steps. Refer to our guide on Common Unit Conversion Mistakes to learn more.

Quick Reference — Kilograms to Pounds (and Related Aviation Units)

To convert standard masses and volumes in aviation, you can refer to the following conversion parameters.

Frequently Asked Questions