THE GIMLI GLIDER
How a Unit Conversion Error Made the Skies a Little Less Friendly
A flight from Montreal to Edmonton is about 1,800 miles or 2,900 kilometers long. As you probably already knew, these distances are the same, just with a different unit of measure. But getting the units of measure wrong can cause problems—as Air Canada Flight 143 discovered firsthand.
Most of the world uses the metric system (meters, liters, and grams), while a few countries (the US, Liberia, and Myanmar) use the “customary” or “imperial” system: feet, gallons, and pounds. Canada was one of the latter countries until 1970, when the nation began to change to the metric system. The full process of changing over took about fifteen years, with one of the last industries to change over being airlines (which, given the expense and longevity of the equipment makes sense).
On July 23, 1983, Air Canada Flight 143 was one of the earliest flights to use the new metric units. Unfortunately, Air Canada was also undergoing a second change at the same time: smaller flight crews. Typically, there were three core members of the crew: the pilot, copilot, and flight engineer. Flight 143, though, didn’t have a flight engineer, so the preflight fueling protocol fell to the pilot and copilot. This protocol required them to convert volume (liters) into mass (kilograms) in order to figure out how much additional fuel was needed for the flight. They did exactly that—except they got the labels wrong. Instead of figuring out how many liters of fuel the plane needed to hit the required amount of 22,300 kilograms, the crew calculated how many liters were needed to hit 22,300 pounds. Because of this error, they ended up with 10,100 kilograms of fuel—about half the amount required to reach their destination.
Having half the fuel needed, of course, means you’re only getting halfway to your destination, which—when the vehicle in question is an airplane cruising 12,500 meters (41,000 feet) above the ground—is a problem. The onboard computer (which was fed the wrong data) didn’t give them warning until it was too late. The left-side engine died, then the right, and because most of the plane’s flight instruments were powered by a fuel-driven electrical system, those soon went dark too. The plane was going down.
Luckily, the pilot and copilot were better at flying than math. As The New York Times reported after the incident, the pilot had ten years of glider training under his belt, and his copilot had trained at RCAF Station Gimli during his days with the Canadian Air Force, so he knew the surroundings quite well. Together, they were able to land the plane—gliding the last 100 km (60 miles)—touching down just an hour or so before nightfall. The plane (the Gimli Glider, as it would henceforth be known) suffered some damage to its nose, and a few tires were blown out, but the passengers were safe. Ten people suffered minor injuries, but there were no fatalities.