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Comment by vic-traill | Hacker News Reader

I expect that most folks would be surprised to hear that Captain Bob Pearson was demoted for six months [0] after this landing, in which he side-slipped a commercial airliner with no functioning engines, and dodged two kids on bicycles on the Gimli 'runway' (read drag strip).

Talk about a uniquely Canadian story - running out of fuel because of a mistake in Imperial to Metric unit conversion. This from someone who was in high school in 1978, The Year Dope Dealers Got an 'A' in Math.

And if you don't get that joke, you're not a Canadian who grew up in the transition from Imperial to Metric.

[0] https://en.m.wikipedia.org/wiki/Gimli_Glider

[edit: duh, added the reference. I get it, after having it being explained to me. Thanks folks. ]

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IIRC they put a few other aircrews into the same scenario in simulators, and they all crashed. I think what the crew accomplished here is one of the most impressive and inspiring human feats I've ever heard of; more people should be familiar with the story.

Like, sure, Pearson had glider experience... but he applied that experience flawlessly in an aircraft with a brick-like glide ratio, landing with no slats or flaps, all the while losing control authority as the airspeed dropped and made the RAT less and less effective, with 69 human lives at stake. Holy shit.

For anyone who's interested, Wikipedia is full of these stories of disasters and near-disasters, and they make for interesting reading.

A glide ration of 12:1 is not great, but isn't exactly brick-like either. A Cessna 172 has a glide ratio of about 9:1. Pilots spend a lot of time practicing gliding in airplanes like that (Cessnas, Pipers, etc) during primary training.

I doubt they practice it much in 767s, though, despite the fact that they actually glide better. :)

You usually don't practice gliding when learning how to fly a small aircraft, they simply don't glide very well.

What you of course do are power-off landings – on airfields, for example from the downwind, and simulated, i.e., you make a go-around just before landing, outside an airfield. Sometimes, it works, sometimes, it doesn't, there are many factors … that's why you actually fly with power idle and not with power off. There're still a few incidents, i.e., somehow the practice becomes tool real!

All in all, power-off landings and other emergency training are an important part of becoming a pilot but you don't spend that much time for them. Other things are much more time-consuming in a typical 45-hour syllabus.

Related fact: the glide ratio does not depend on the aircraft weight, only on the aerodynamic efficiency (the ratio between your lift and your drag), so it is useless to throw weight to reach further like maybe you have seen sometimes on movies. Less weight will make you descend slower but not further. Normally, the longer your wing, the higher your efficiency. See for example the pictures here: https://en.wikipedia.org/wiki/Aspect_ratio_(aeronautics)

Losing weight will reduce stall speed, allowing for a slower and safer landing. Modern competitive gliders carry a substantial quantity of water ballast - the extra weight improves glide speeds, but it can be jettisoned before landing.

I fly a paraglider with a 9:1 glide ratio and I think it's quite a good number, so 12:1 is definitely not brick-like to me..

12:1 is actually not bad.. A classic glider trainer (SGS 2-33) in average condition is just a bit better.. The difference is the best glide speed. 50mph vs 150mph.

Slipping to lose altitude fast is a regularly trained maneuver for glider pilot.

Still an amazing feat to pull that landing.

The 2-33 is speced at a glide ratio of 22:1. You might be thinking of the 2-22 which is speced at 17:1.

As someone who learnt to glide on modern (30:1 glide ratio) glider, those numbers make me think of truly ancient hardware...

You're recalling a different incident: engine-out problems are a routine part of flight training at every level.

You're thinking of https://en.wikipedia.org/wiki/United_Airlines_Flight_232

where so much of the plane broke that they had to invent a new way to fly it.

I can't turn up a reference right now, but like you say, in the next few years that failure was repeatedly simulated, and all the simulated planes crashed.

(IIRC, Haynes declined to try his hand at any of the simulations, explaining that the one time when it really mattered was enough for him.)

Looks like Wikipedia thinks they also simmed the Gimli Glider incident with other aircrews, though it may well be wrong: https://en.wikipedia.org/wiki/Gimli_Glider#cite_note-19

Flight 232 is another very interesting story, for sure.

You're right, thank you.

The reason he had to side-slip the aircraft was because the RAT doesn't generate enough power to operate the flaps.

Why are you saying this?

Aren't flaps used to lower stall speed?

I have flown gliders at a beginner level (so no flap) and the reason we did side/straight ahead slips was because we came in too high (emergency procedure or bad estimation) and would have ended up touching down too far with not enough space left to land safely.

They are, but as I understand it the RAT doesn't generate enough power to operate the flaps in general once you get down below a certain speed.

Flaps do lower the stall speed, but they also make the glide ratio worse, so you descend more steeply.

But that is a side effect of flaps. So what you are saying is that they had planned their pattern assuming they would be able to extend flap on final but couldn't and ended up too high?

I assumed they came in a bit too high as an insurance (you can burn height but can invent it), but just ended up with a lot more than they expected just because if their lack if familiarisation with the situation in that plane, so much that the dive break alone weren't sufficient to burn it.

Yes, typically you'd want to come in a bit high (or fast; you can always trade speed for altitude to an extent).

Then, you put in flaps to have a less efficient wing profile and descent more steeply (without gaining excessive speed).

However, here they did not have enough power to do that, so the Captain put it into a slip: flying uncoordinated, with (say) left rudder, but right aileron, flying somewhat diagonally (or rather, flying straight ahead still towards the runway, but presenting not only the nose, but a bit of the aircraft body to the wind).

That gets you down quite well.

Those are really the techniques when you're too high on the approach: 1. Flaps 2. Slip 3. S-Turns

Flaps do 2 things: smaller flap deployments increase lift without increasing drag much; larger increase drag without increasing lift much (beyond that of using flaps at all).

You want to be going as slow as possible when you land (aircraft make poor racecars), and most aircraft call for some level of flaps on landing. Increasing lift lowers the stall speed, which is good, and increasing drag allows you to lose altitude without gaining speed. Without flaps they would have to land too fast.

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I couldn't believe the suspension! What a feat landing that plane.

Landing the plane was incredible, but having the plane take off without enough fuel was outright negligence. I'm pretty sure the airline industry is more keen to have pilots who follow procedures and avoid risks in the first place than heroes that miracolously solve trouble they created.

Not that the pilot was the only one responsible off course, but he had his share of blame in the whole thing.

They did follow procedures, actually...

why do you do [0] and never put any [0]() =(

CS man! What can I say? :-)

No, he means, where's the reference? I would be like if I said:

Scientists recently proved the existence of a soul inside of all life forms [0].

Well played, sir!

Every CS paper I've had to write required valid references [1]

Indeed. Unterminated references are a sure sign of sloppy thinking[0].

They can also be dangerous[1]: gaze into the void, and the void gazes back. Cast into void, and you might get a null pointer exception.

Wait, Canada converted from Imperial to Metric? Wow that's amazing! I wish the US would do the same.

Only 3 countries in the entire world have not adopted SI units.

Actually Liberia and Myanmar have been converting to Metric, so the USA is likely the last place where people are not being taught Metric. Unless it's improved and Metric is being taught in American schools?

Metric has been taught in most American schools since the 70s. Nearly everyone here learned it at some point, but most people don't use it day to day, so they don't think in it.

yeah but its not like its pushed much outside of chemistry. my niece and nephew have learned less about it than I did over thirty years ago.

it simply is not a priority, it could be slowly slipped into prominence by emphasizing the measurements on everyday items instead of making those in small print

>yeah but its not like its pushed much outside of chemistry

Every science class I had in high school used metric. We also spent a fair amount of time going through it in elementary and middle school math classes.

My younger sister (by 20 years) spent a good deal of time on the metric system in her math classes.

My science education, at least in secondary school, was all in metric. I graduated from high school in 2003. The issue is that it isn't used here in everyday life, so it becomes "that weird thing from science [which I already disliked because of the math]".

I've done experiments switching to metric. It's not a good idea to rely on my GPS for speed limit information. My home thermostat apparently doesn't have a Celsius setting (and would confuse my wife if it did). It's difficult, but mostly possible to switch here...but what's the point? It's a lot of work for comparatively little benefit.

I was taught metric and its merits over other systems in public school, but I'm sure it varies across the country.

In theory the UK is fully metric. In practice isn't not.

It is the same in Canada. F.e. Supermarkets advertise the price per pound (presumptively because it is smaller)

American influence on Canada means they have oven temperatures in Fahrenheit, recipes in cups, American paper sizes, furniture and buildings in inches etc.

Britain has all of this in metric; the beer, road signs and casual (non-medical) body measurements are the only exceptions.

Ontario build code is hilarious. For example, table 9.23.10.1 specified the size and spacing of studs in walls. For interior walls, the maximum stud spacing is 406mm on center, and minimum stud size is 38x38mm.

If you didn't know this was 16" on center, and 2x2 framing, you'd think some mad drunk person had come up with these numbers. I also like to imagine building inspectors walking into a building and saying "Oh, these studs are 407mm apart. Tear the building down."

And in official government communication, it is nominally metric, but you'll see things in e.g. building codes like "hallways must have a width exceeding 914mm", which is really just 3 feet.

They partially did since 1975[1].

[1] : https://en.wikipedia.org/wiki/Metrication_in_the_United_Stat...

The US doesn't use imperial units. It uses customary units. An imperial pint is 25% larger than a customary one.

Metric conversion in the UK isn't complete: on road signs, distances are in miles and speeds are in miles per hour. Pints are used to serve draught or keg beer.

In aviation, height/altitude is measured in feet or flight levels (hundreds of feet), horizontal distance is measured in nautical miles, and speed is measured in knots.

I found this really surprising about the UK. Most of the other common wealth nations (Canada, Australia, NZ) all have their signs in metric.

>Pints are used to serve draught or keg beer.

Even in France, we use pints to serve beer...

Sure, but it is a normal metric pint (0.5L) - and the demi is 250mL.

In the UK and US they still have ye olde measures - 568.3mL and 473.2mL respectively.

AFAIK US pints for aren't 568ml. Whoever said everything is bigger in America didn't include the beer.

Except the french pint is metric (50 cl).

yes but only for beer in bars though.

Pints are sold as pints but its marked up as 568ml on the glass.

Milk was the same for a while and you still see it occasional though we've gone to liters mostly.

Most things are metric now though.

With milk, the measurements used seem to depend on the type of milk sold. If it's regular milk, it will be sold by the pint. If it's UHT or filtered milk, it seems to be sold by the litre.

Nautical miles and knots kinda make sense because "Historically, it was defined as one sixtieth of the distance between two parallels of latitude separated by one degree."

Feet for altitudes are not ideal, but it's become a convention (in China they use meters) (Now if they were to mix feet and miles in the altitude that would have been bad)

We did. Except we still use feet for height and pounds for weight, commonly

Haven't most hospitals switchwd to kg and m?

Construction on the other hand is still mainly in imperial/US units, which makes sense given that the use the same material providers as the US.

In most English-speaking, metric-using countries, hospitals use the metric system for measuring weight and height, but it's common to still hear imperial units used in casual conversation. In Australia I definitely still hear people talking about height in terms of feet and inches. Weight tends to be in kilograms these days though.

This is fairly new in Canada. 10 years ago (long after the conversion to metric), hospitals and doctors used to speak in feet/pounds. As they have switched to metric fairly recently, I expect people to slowly get used to it and soon starting using metric for height and weight as well.

Britain has switched entirely to metric in healthcare, removing the last "friendly" bit of communicating to patients in Imperial.

The risk of confusion was too high, and there was at least one case of a severe overdose when a weight was accidentally given in pounds rather than kilogrammes.

If an American child was hurt outside the USA, and the parent overheard the nurse saying their weight was 55kg, would they know whether that's accurate? That's why it's important that the same units are used at home and in science.

I recently read a blog post where the author described his current weight and his weight as a student in stones.

That's why I voted for Lincoln Chafee in the primary. [0]

[0] https://www.youtube.com/watch?v=WI4n5OdqWfw

It's boggling that the US hasn't moved over yet. At a minimal, all Interstate speed limit signs should be required to have both mph and kph (there are a few highway signs like this, but they're rare). Mandate in 8 years, they'll be kph only.

The US is a huge country. Just to replace the road related signs alone means replacing or modifying hundreds of thousands of signs. There's mile markers (at least 48,000 alone given the 46,876 miles of interstates in the US), exit signs, distance to destination signs, and speed limit signs. These signs are rarely replaced unless they're damaged so 8 years would still require a lot of unexpected maintenance.

Yes, and if you had started in the 1970's it would have been done by now. But since the press thought it was "dictatorial", there wasn't much interest at the time. So now you have 40 years of new signs to replace :-)

Why? Most industries that should be using metric already do in the US. Cars use metric fasteners, etc. When i worked in a lab, everything was metric.

Imperial is only really used in consumer facing situations. If we forced everything over to metric, would it make that much of a difference? Would the US economy suddenly surge due to a more efficient system? Unlikely.

But the consumer-facing side is the largest side. Think of all the extra bolts sold, all the new signs needing changing. This will be a great economy surge! :-)

Familiarity and ease of conversion, plus compatibility with the rest of the world.

I think the US could gradually move to metric, but as with the UK, there's no need to replace miles as a distance measurement. In some ways, I think it'd be nice to always keep mph/miles... but otherwise, for weights and measures, metric would be superior.

And hey, if it's good enough for NASA, it's good enough for the rest of the states. ;)

Worst hit, would probable be the automobile industry. But I'd say there'd be advantages to metrification there too.

> Worst hit, would probable be the automobile industry

They use metric.

> I wish the US would do the same.

Why? The French system has exactly two benefits: it's popular, and it's easier to perform abstract conversions (i.e., conversions between units on paper). OTOH, it is worse at performing concrete manipulations (i.e., dividing one physical quantity into another): accurately cutting or dividing quantities into tenths without the aid of a guide of some sort (e.g. a ruler or measuring cup) is so difficult as to be basically impossible, while cutting or dividing into halves is so easy that a child can do it, and thirds are not much harder at all.

Yes, it happens that it's easier to 'do science' currently using French units, but that is because all of the standard constants happen to be based in those terms: there's no fundamental reason one couldn't use Rankine instead of Kelvin and so forth.

I won't claim that the standard system of units is perfect (the partial decimalisation the Brits attempted in the 19th century was misguided): indeed, it could get a lot better: nautical miles are probably better than statue miles; a reset in the length of the yard so that there are 1,728 yards in a mile would probably be a decent idea; a cup ought to be 16 cubic inches; and so forth.

But throwing away 12 (with its divisors of 6, 4, 2 & 3) for 10 (with half as many: 5 & 2) was a foolish, foolish decision by the French.

If they'd really wanted to be revolutionary, they'd have adopted base-12 numbering instead of trying to fit the world to base 10.

(I will grant the the French system of paper sizes is elegant, and I wouldn't mind us adopting a similar system based, of course, on the yard)

The times when the measurement can be divided by 2 are either so rare as to be irrelevant (the room isn't an even number of inches long anyway, and adding feet makes the calculation worse) or arrive by design (my dishwasher is 900mm wide, check the factors in that).

The paper sizes are German, and adopted by the ISO.

In physical trades like carpentry, brewing, farming & so forth, being able to easily halve, double or treble quantities is quite convenient. The customary units, being based on powers of 2 (with a few 3s thrown in …) tend to be really good at this, as anyone who's ever brewed or handled produce in standard units knows.

Dealing with French units is a pain.

(as an aside, the reason I call them 'French units' is because the name 'metric' privileges them: our standard units are no less a system of measures than are they; this too is my problem with 'SI,' since our system is (or was) likewise international)

> the reason I call them 'French units' is because the name 'metric' privileges them

I guess, but for what it's worth, I've never heard that before. It's a poor way to communicate, if communication is your goal.

And really they are SI units, the 'International System of Units', which may or may not 'privilege' them, but is certainly both correct and normal usage.

The dishwasher was intended as an example for carpentry: standard kitchen cupboards etc are made in multiples of 300mm. It's the same for things like floor tiles, doors, etc.

No farmer or brewer deals in units that are easier to half in American rather than metric units. They use tonnes, hundreds or thousands of litres, and large areas. Outside America, they don't need to convert between units of the same type: no acre-feet, bushels, pounds, tons, or all that crap.

Calling them "French units" sounds like xenophobia. The American system was never international, and the British system didn't extend that much further than the French, at the time of the empire.

> They use tonnes, hundreds or thousands of litres, and large areas. Outside America, they don't need to convert between units of the same type: no acre-feet, bushels, pounds, tons, or all that crap.

In America, anyone who would deal solely in tonnes can deal solely in tons; anyone who would deal solely in hectolitres can deal solely in barrels (traditionally, 128 quarts); anyone who would deal solely in kilolitres can deal solely in tuns (traditionally, 1,024 quarts). No-one in America has to say '7 tuns, 2 hogsheads, 3 gallons, six quarts and a fluid oz' any more than he'd say '7.2850546 kilolitres.'

> Calling them "French units" sounds like xenophobia.

Oh, I'm not xenophobic! I just don't think they deserve a privileged position.

> The American system was never international, and the British system didn't extend that much further than the French, at the time of the empire.

The American system was used in Liberia; prior to the Russian Revolution the majority of the peoples of the world used systems of measurement substantially similar to the Anglo-American system, and could (should have, IMHO) rationalised and standardised that, rather than adopting the objectively inferior decimal principal.

> anyone who would deal solely in tonnes can deal solely in tons

Then your argument that these quantities are easily divided is irrelevant.

> 7.2850546 kilolitres

My house's water meter measures up to 99,999.999m³, or in litres up to 99,999,999 litres.

Europe other than Britain and Ireland didn't use the British system, and neither did their colonies, China, Japan, etc. All the British colonies except the USA chose the metric system after independence.

The SI system is the only one that's truly international, set up by international treaty between many countries.

That pesky Napoleon, spreading his nonsense units all over the place without regard of consequences. Didn't he learn his lesson on Waterloo?

DIN (Deutsche Industrienorm) paper sizes, by the way, are beautiful:

A0 is 1 m^2, by area, with sides in a ratio of 1:sqrt(2).

When you fold it in half, you get the same ratio, but now A1:

A1 is 1/2 m^2.

A2 is 1/4 m^2.

A3 is 1/8 m^2.

A4 is 1/16 m^2.

etc.

So, if you buy paper, it will be, say, 80 g/m^2. Now, one page of A4 thus is 5 g.

By your count, it seems that the metric system (do you call it the French system to devalue it? seems like it) has 3 points: elegant paper sizing, easier to do science, and popularity.

By your count, the "standard" system (how is it standard if it's used almost nowhere?) has 1 point: A foot being 12 inches means it has more divisors than 100 cm to a metre.

So, therefore the final score based on your appraisal is Metric 3, Freedom Units 1.

A clear win for the metric system.

> Freedom Units

Top marks!

Where does the term "freedom units" come from?

Historically, it seems baffling. Their real name, "imperial units", are a clue that they're all but rooted in freedom. They're inherited from the country that the US broke free from…

Plus, the Metric system stems from the French Revolution, making it a better contender for the term "freedom units".

Finally, wasn't there a whole PC phase in 2003 where expressions with "French" in it, like "French Fries", were renamed "Freedom Fries"? It all makes things rather confusing.

The last time that I cheeked it, we had ten fingers and we use a base 10 numeric system. I don't find why would a base 12 system be more natural.

Oh my, metric is so much nicer.

Yes, easy halving and quartering was important back when the population was not used to decimals. But surely, most people these day can tell that half of 100 cm is 50 cm, a quarter is 25 cm, and a third 33.33 cm.

So, the Gimli glider had a glide ratio of 12:1. We're 10 km high, how far can we glide? Well, 120 km.

That's how we'd compute it in a metric world. In the real world, the Gimli glider was 32,000 feet high. How many nautical miles can it glide? Quick?

> In the real world, the Gimli glider was 32,000 feet high. How many nautical miles can it glide? Quick?

In the real world, the Gimli glider was 9,753.6 m high. How many km can it glide? Quick?

Of course, in real life one would cheat: a nautical mile is about 6,000 feet, so 32,000 feet works out to about 5 nautical miles, which means that it can glide about 60 nautical miles. One can always grab a calculator (or slide rule — they're actually quicker at this than calculators) to be certain (12:1 at 32,000 feet gives 63 nm/110 km).

> In the real world, the Gimli glider was 9,753.6 m high. How many km can it glide?

117,043.2 m. In about 5 seconds in my head. By doing value × 10 + value × 2. Because multiplying by 10 is so easy, because arabic numerals are in base 10.

And by cheating, which obviously we would do as a first approximation, it is also much more trivial in SI units: 9,753.6m is about 10km, × 12 → 120km. At most 1 second to find. Faster again.

But my fundamental point: we already have the mnemonics ready for base 10, and we won't switch away from arabic numerals any time soon, so we might as well benefit from it.

It isn't a competition. After all, the metric system is screwed up: having 60 seconds in a minute is a pain (but wow, so many divisors! — really though, just an inheritance of an ancient culture that did not use base 10 numerals; using higher bases isn't an indication of modernity) and the fundamental definition of the second doesn't map to any physical reality in an intuitive way anymore.

It is simply less screwed up.

I'm confused, you think 12 is a better base unit to use than 10? Do you think we should all be counting in hexadecimal too?

> I'm confused, you think 12 is a better base unit to use than 10? Do you think we should all be counting in hexadecimal too?

No, in duodecimal. It's generally better: https://en.wikipedia.org/wiki/Duodecimal

And you can count by twelves on the knuckles of your fingers, so anyone who still needs to count on his fingers can still do it (I'm not certain why this is such a selling point for decimals: surely we're all intelligent enough to use higher bases?).

There are countries that use the metric system, and countries that land on the moon :)

Rather Dude-like wisdom, my chapeau off to you, sir

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