I like the story of the Gimli Glider. It’s a feel-good true story, for days when a person needs a feel-good true story; it’s invaluable as a case study for my students; it’s also good for putting problems into perspective on a hard day.
If the name gives you surreal images of a Middle-Earth dwarf wielding an axe in a sailplane, you might be relieved to learn that the reality is very different, though equally surreal in some ways.
It’s the true story of an airliner that ran out of fuel at 41,000 feet, because of a misunderstanding about whether it had been fuelled in litres or in pounds of fuel. At that point, it became the world’s largest glider. The co-pilot recommended an emergency landing at Gimli airfield, which he knew from his days in the Royal Canadian Air Force. The pilot landed successfully, largely because he happened to know a lot about flying gliders. Nobody died; everyone walked away, with feelings of disbelief and massive relief. Even by the standards of movies about fictional aircraft in jeopardy, it’s quite a story.
So how do you manage to run out of fuel at 41,000 feet? It’s a classic example of what’s known as a normal accident. In 1983, when this happened, transition from Imperial to metric units was a live issue. To anyone familiar with complex systems and human factors, it was a disaster waiting to happen. Sooner or later, someone would use the wrong units, and something would go horribly wrong. That doesn’t mean that the decision to make the change was wrong; usually in life, there isn’t a completely risk-free option, which is why professionals in the field think in terms of risk management and risk reduction rather than risk elimination.
Refuelling an aircraft is a very different proposition from refuelling a car. One big difference is that you deliberately don’t fill the fuel tanks up completely unless you really have to. This is because fuel is heavy, and you don’t want to haul more weight through the sky than you have to. When you’re refuelling an aircraft, you work out how much fuel you’ll need for your flight, and then put in that much plus a bit extra as a safety margin, to keep the weight down. That process has quite a lot of room for error, which is why there are numerous checkpoints in the procedure to reduce the risk of those errors. When Air Canada Flight 143 was being refuelled, the procedures for refuelling had recently been changed. On top of that, there were some mechanical problems with the fuel monitoring system, and to round things off, one of the people involved was distracted part-way through the procedure. The pilots double-checked the figures, but because some of the numbers they had been given were inaccurate, the double-checked results were wrong. So, in summary, nobody was silly, everybody was conscientious and sensible, but a whole batch of individually minor problems all happened at the same time, so the error slipped through.
The odds of that string of events happening are pretty slim, but when you’re looking at a field like aviation, where there are very large numbers of flights every day, then slim odds come up more often than anyone would like.
In brief, the engines ran out of fuel about half-way through the flight. The First Officer, Maurice Quintal, suggested that they land at the Gimli airfield in Manitoba. Captain Bob Pearson managed to land the plane safely, despite the fact that the runway involved had been decommissioned and was being used for a sports car race at the time of the landing. The two pilots were initially reprimanded and punished, on the grounds that running out of fuel in mid air wasn’t something that aviation authorities approve of. Soon afterwards, when several other crews had tried to pull off the same landing in flight simulators and had all crashed, Pearson and Quintal were given medals, on the grounds that landing safely was something that aviation authorities strongly approve of. The full story is even more colourful and improbable (including the part about the three children on bicycles at the end of the runway who were unaware that they were being followed by a landing airliner, because it wasn’t producing any engine noise).
The feel-good aspect of the Gimli Glider story is easy to describe. Human beings face a life or death challenge, and rise to that challenge; everyone plays their part, and the story ends happily for everyone involved. One of the striking features of the movie based on this story is that there’s only one token obnoxious passenger, and you get the impression that he was inserted by the scriptwriters because they didn’t think that anyone would believe the script otherwise. (On the other hand, it was an Air Canada flight, so maybe audiences would have happily accepted that the passengers would feel culturally obliged to be quietly, politely heroic and can-do…)
In terms of a case study, it has a lot going for it.
For starters, there’s the consideration that nobody died or was seriously injured. That’s a huge plus. Most case studies about safety-critical systems involve something going bang, followed by people dying. There’s a lot of human tragedy in safety-critical systems studies. You don’t want to traumatise students by getting into the grisly details of cases where people died horribly, so a case where everyone walked safely away is very welcome.
Another issue is that if you’re going to work in that field, with the aim of preventing future tragedies, then you need a coping strategy so that you remain able to function. Two common strategies are to develop a dark sense of humour, and to treat the cases as intellectual challenges. Both these strategies can fend off burnout and emotional breakdown for quite a while, but they can both be seriously misunderstood by people outside the field, since they can both look like not caring or not taking human life seriously. Again, the Gimli Glider works well as a case study, since there are quite a few moments of dark humour in the story, but because there’s a happy ending, this is easier for people to handle. The humour in this case isn’t a coincidence. This leads into another reason that I like to use this as a case study.
As I’ve mentioned in a previous article, a major feature of humour is that the same situation can be explained in two very different ways. That’s what happened with the refuelling of the Gimli Glider. There was a sequence of misunderstandings, all of which made complete sense in relation to one key assumption (that the aircraft fuel measurements were in kilos). Unfortunately, the refuelling sequence was also a perfect fit with a different key assumption (that the aircraft fuel measurements were in pounds).
The punch line is the place where the audience realise that they’ve been using the wrong mental model for what’s happening, and that they need to switch to a very different model. That’s just what happens when the pilots of the Gimli Glider, and the students hearing the story, realise that the plane had been filled up in Imperial rather than in metric.
If this new model leads to death and injury for real people, then we’re looking at a tragedy in the classical sense. However, this also has the same structure as a joke. Dark humour involves recognising the humour as well as the tragedy, and this can lead to a lot of mental unease among the audience. In the case of the Gimli Glider, there isn’t any death or serious injury, so the students can see the underlying misunderstandings and alternative explanations without the complication of mental unease about the consequences.
There’s a lot more in this case study, about organisational behaviour and systems theory and human factors and numerous other issues. I won’t go into detail here; instead, I’ll move on to the third main reason that I like this story.
The Gimli Glider story is great for putting most worries into perspective. Imagine that you’re on that flight, on your way home, fretting about how to tell your parents that your exam results weren’t what you wanted. How would you and your parents feel about those exam results as you walked away from the aircraft, with the rest of your life ahead of you, and inspirational music bringing in the closing credits?
On which positive note, I’ll end.
Notes and links
Sources of images used in this article:
“K21 glider” by Paul Haliday – http://en.wikipedia.org/wiki/Image:K21_glider.jpg. Licensed under CC BY-SA 3.0 via Wikimedia Commons – https://commons.wikimedia.org/wiki/File:K21_glider.jpg#mediaviewer/File:K21_glider.jpg
(Used under fair use terms, as part of an article about the research context of the flight.)