Gliding home

In 1983 a Boeing 767 with 61 passengers ran out of fuel while twelve thousand metres off the ground. The metric system was to blame.

Gimli Glider
Aero Icarus from Zürich, Switzerland [CC BY-SA]
Hey hey, it’s another one of my posts about the metric system! Much like the metric / Imperial confusion that crashed the Mars Climate Orbiter, the crisis on Air Canada Flight 143 between Montreal and Edmonton in Canada was the terrifying result of human error.

When a plane refuels the flight crew (the flight engineer or the pilot) must calculate how much extra fuel they need. It’s a pretty simple calculation: work out the fuel requirements for the trip, subtract the amount of fuel you already have, and fill the plane up with the difference. However, in 1983 Canadian aviation was in the process of switching from Imperial units to metric. When the fuel requirements for this flight were calculated some Imperial units snuck back in by mistake. The result: the plane took on only one quarter of the extra fuel it needed.

Unfortunately, the plane’s fuel gauges were off, so no-one noticed this problem until exactly the wrong time: halfway through the flight, 12,000 metres up.

Out of fuel, one of the engines shut down. No worries, we have another engine! Then the second engine shut down. No worries, we can glide home! Then the cockpit went black – most of the instruments were powered by the engines.

(Side note: this reminds me of a lyric from They Might Be Giants’ Shoehorn with Teeth: “Tour the world / In a heavy metal band / But they run out of gas / The plane can never land.” Sorry.)

Everyone on that plane was extremely lucky: the pilot was a big fan of gliders, and so he knew quite a bit about unpowered flight. He and the first officer began to furiously calculate: how fast were they descending, and where could they land before they ran out of time? Talking with a nearby air traffic controller, they picked out a former air force base runway in Gimli, Manitoba.

One more problem: the runway had been converted to a car racing track… and a race was on at the time. And the pilots didn’t know this. And, because the engines were off, the plane was silent.

The 767 came gliding down towards the runway to the shock of onlookers – including two kids on bikes directly in the path of the descending plane. (You can see an interview with one of them 35 years later in the video below.) The plane landed on a drag race strip, smashing into the central dividing line, and came to a stop. Everyone survived, and the plane itself was restored to full service; it was retired twenty-five years later.

[Thanks to Ann S. for suggesting this topic.]

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