The Gimli Glider, the Fuel Unit Error That Silenced Both Engines of Air Canada One Forty-Three, and the Fuel Planning Lesson Every Pilot Should Know Before Leaving the Ramp

On July 23, 1983, Air Canada Flight 143 - a Boeing 767 - ran out of fuel at 41,000 feet over northwestern Ontario because a ground crew multiplied liters by the wrong density factor and produced a fuel mass roughly two and a half times higher than what was actually on board. Both engines flamed out. The aircraft glided to an emergency landing at a former military airfield. All 61 people on board survived. The error was not mechanical. It was a unit conversion mistake that nobody caught.

What Caused the Fuel Miscalculation on Air Canada Flight 143?

The 767 was among the first aircraft operated by a Canadian airline to use metric measurements throughout - fuel in kilograms, not pounds. The industry was still transitioning.

That morning at Montreal Dorval Airport, the aircraft’s fuel quantity indication system was inoperative. The approved maintenance workaround required ground crew to measure fuel using physical drip sticks, which give readings in liters.

To convert liters of jet fuel to kilograms, you multiply by the density factor: approximately 0.803 kg/liter.

The crew used 1.77 instead.

1.77 is the density of jet fuel in pounds per liter, not kilograms per liter. Because one kilogram equals 2.2 pounds, every liter measured was multiplied by a factor that overstated the fuel mass by roughly that same ratio. The crew flew out of Montreal, stopped in Ottawa, rechecked using the same methodology, confirmed the same error, and departed for Edmonton.

What Happened When Both Engines Failed?

Captain Robert Pearson was at the controls. First Officer Maurice Quintal was beside him. The left engine went quiet first, followed by the right. The aircraft was at flight level 410.

When both engines flame out in a 767, most hydraulic power is lost. The ram air turbine - a small propeller that extends automatically into the airstream - generates just enough electrical and hydraulic power for limited control authority. Instruments and systems the crew depended on were unavailable or degraded.

Quintal had served at Royal Canadian Air Force Station Gimli during his military career. He knew there was a runway there and knew approximately where it was. He suggested it. Pearson trusted the information and used it. That act of crew resource management - a first officer surfacing knowledge the captain didn’t have, and a captain acting on it - directly contributed to everyone on board walking away.

How Did the Crew Land a Powerless 767?

The 767 without engine power has a glide ratio of approximately 17:1 - seventeen feet forward for every foot of descent. With a runway roughly twelve miles away, Pearson came in high.

He used a sideslip: cross-controlled aileron in one direction and opposite rudder to increase drag and bleed altitude without gaining airspeed. It is a technique taught early in primary flight training. It is not in the standard operating procedure for a 767 approach. Pearson applied it because it was the right tool.

He touched down at approximately 180 knots. The nose gear collapsed on impact. The nose acted as an additional brake. The aircraft stopped. It never flew again.

Gimli Industrial Park Airport - the former military field Quintal had suggested - was no longer an active civilian airport. That afternoon, the runway was hosting a Winnipeg Sports Car Club race event. Cars were on the pavement. Families and spectators were nearby. Nobody on the ground knew a 767 was inbound without power, without radio contact on the advisory frequency.

Sixty-one passengers and crew evacuated. There were minor injuries on the escape slides. No fatalities.

How Does Fuel Unit Error Apply to Your Training Aircraft?

The scale is different. The principle is identical.

Fuel has three measurable properties: volume (liters or gallons), mass (kilograms or pounds), and density, which is what you need to convert between them. For avgas, the planning rule of thumb is approximately 6 pounds per gallon. For jet fuel, the density is approximately 0.803 kg/liter or 6.72 lbs/gallon.

When you do your weight and balance and fuel load calculation, you need to confirm:

• Whether your aircraft’s fuel capacity is listed in gallons or liters
• The difference between total fuel and usable fuel
• Whether your calculated reserve makes sense for your power setting, altitude, and forecast winds

A number that surprises you is information. Investigate before you launch.

What Is Normalization of Deviance, and Why Does It Matter?

The 767’s fuel quantity indication system had been inoperative for a period before the accident. The manual drip stick workaround had been used before and appeared to work. The degraded state stopped feeling like an anomaly and started feeling like normal operations for that particular aircraft.

This is normalization of deviance: a degraded or abnormal condition that has not yet caused a visible problem begins to feel routine. When something is not working the way it was designed to work - when you are relying on a workaround - that is the moment to slow down and verify the entire chain, not just your piece of it.

What Is the Difference Between Fuel Exhaustion and Fuel Starvation?

These are two different emergencies caused by two different failures, and both will cause your engine to go quiet.

Fuel exhaustion means the tanks are empty. That is what happened to Air Canada Flight 143. Accurate pre-flight calculations and conservative reserves eliminate this risk.

Fuel starvation means fuel is aboard but the engine is not receiving it. This can result from a mismanaged fuel selector valve, a blockage, or vapor lock. The fuel exists. The engine cannot access it.

Your engine failure checklist addresses both. The sequence - throttle full forward, carburetor heat if applicable, fuel selector to both, electric fuel pump on, mixture rich - specifically targets starvation scenarios. If the engine quit because the selector was on an empty tank, running that checklist may restart the engine. If the tanks are empty, it will not. You run the checklist either way, because you owe it to yourself and your passengers to eliminate every recoverable possibility.

Before any of that, you establish best glide.

What Should You Do First During an Engine Failure?

In the Cessna 172, best glide is 68 knots. In the Piper Cherokee 160, it is approximately 73 knots. Whatever aircraft you train in, that number needs to be automatic before you need it.

The sequence is Aviate, Navigate, Communicate - and that order is not arbitrary.

The moment the engine goes quiet, lower the nose and establish best glide speed. That happens immediately, before the checklist, before the radio. Then scan for a landing area within gliding distance. Then run the checklist. Then communicate.

On your practical test, when the examiner pulls the throttle, the first thirty seconds reveal whether you understand this priority order. They are watching to see if you fly the airplane first. The checklist follows that setup. If your first instinct is to reach for the POH, you have already mismanaged the emergency.

Key Takeaways

• Unit errors in fuel calculations are catastrophic at any scale. Always confirm whether you are working in gallons or liters, kilograms or pounds, and apply the correct density factor for the fuel type.
• Verify that every calculated number makes sense. A surprising result is not a reason to proceed - it is a reason to stop and find the error.
• Normalization of deviance is a real hazard. A workaround that appears to function is not the same as a system that is working correctly. Do not let an abnormal state become your new baseline.
• Fuel exhaustion and fuel starvation are different problems with different causes. Both require the same first action: establish best glide before anything else.
• CRM works in single-pilot operations too. Quintal’s memory of a former military field saved sixty-one lives. The people around you - controllers, instructors, other pilots - know things you don’t. Use what they know.
• The Canadian Aviation Safety Board’s accident report from this incident shaped how airlines worldwide document and manage deferred airworthiness items. Captain Pearson received the Fédération Aéronautique Internationale’s Diploma for Outstanding Airmanship.