
Gimli Glider - numlocked
https://en.wikipedia.org/wiki/Gimli_Glider
======
vic-traill
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](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. ]

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

~~~
zeveb
> 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)

~~~
na85
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.

~~~
espadrine
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.

------
koliber
So it turns out that passenger jets do not carry backup batteries. This poses
problems when all engines fail, as many functions are fly-by-wire, and require
power.

Th RAT comes to the rescue in such situations. Its a Ram Air Turbine which
pops out of the body when called upon. The turbine spins and generates just
enough electricity to power the crucial instruments and controls.

I was touring a Hamilton Sundstrand factory a long time ago that manufactured
these RATs. They had a tally board up that listed situations where the RAT was
deployed and the number of people that survived the incident.

Talk about being motivated to do a good job!

~~~
repiret
The RAT is backup power for the hydrolics. Do you have a citation that there's
no backup battery for the electronics, because I don't believe it. Even for
the crappy 25 year old not-approved-for-IFR GPS I had in my Cessna needed the
engine/alternator to fail plus two separate batteries to drain before it would
turn off. I can't believe the electronics on a fly-by-wire airliner are less
redundant.

~~~
464192002d7fe1c
RAT provides electrical generation too. Its all layers of protection, there
are batteries for limited duration and limited equipment. RAT provides more
(duration and functionality).

There are some components that are considered like that GPS that have small
enough power requirements and are critical enough that they can have
significant battery and others that are powered by the RAT, and yet others
that just don't work with a main engine failure.

Highly suggest watching some of the Mayday episodes about the power failure
incidents like Gimli, its very educational.

~~~
caf
Yes - the electrical generators are generally powered off the hydraulic
system.

------
jasoncartwright
Semi-related story -
[https://en.wikipedia.org/wiki/British_Airways_Flight_9](https://en.wikipedia.org/wiki/British_Airways_Flight_9)

"Ladies and gentlemen, this is your captain speaking. We have a small problem.
All four engines have stopped. We are doing our damnedest to get them going
again. I trust you are not in too much distress"

~~~
464192002d7fe1c
How delightfully British.

~~~
techdragon
So British I can't help but think of the Airline Pilots skit from "How to
Irritate People" \-
[https://en.m.wikipedia.org/wiki/How_to_Irritate_People](https://en.m.wikipedia.org/wiki/How_to_Irritate_People)

------
ihunter
A few things came out of this incident:

1) Per my first flight instructor, this is the reason students now learn how
to forward slip. Up until then it was just viewed as a glider move. Thankfully
the captain was an experienced glider pilot. It's required to demonstrate this
maneuver for your private license (not sure about sport license).

2) This ultimately led to overhaul and standardizations for fuel / weight
calculations.

3) Because the engines powered the electrical systems via the alternator, the
plane lost a number of electrical systems until the ram air turbine kicked in
(amazing little invention and kinda saved the day). Afterwards, many
subsequent aviation systems were designed to be operated independently from
requiring the alternator to be running.

Good documentary/recreation on the incident:
[https://www.youtube.com/watch?v=Bct1mWUp8to](https://www.youtube.com/watch?v=Bct1mWUp8to).
Miraculous that everyone survived, the captain deserves an accolade for quick
thinking.

~~~
walrus01
> 2) This ultimately led to overhaul and standardizations for fuel / weight
> calculations.

You have _no idea_ how hard it is to get Americans to use 100% metric
everything, even in the year 2016 in a highly technical field. It's incredibly
frustrating. I'm amazed at the number of people under age 30 who have clearly
not been taught even the basics of the metric system in middle school and high
school, or intentionally disregarded/forgot it.

Working in the US domestic economy is unavoidable to do many things in US
customary units when construction/physical engineering of things is involved.
For example if building mission critical telecommunications towers to EIA/TIA
222G standards, everything is going to be in US customary units (the tower
structure itself, the fasteners, the guy cables, the anchors, the
foundation/concrete job, the dimensions of the equipment shelter, the
electrical conduit, etc).

~~~
zeveb
> You have no idea how hard it is to get Americans to use 100% metric
> everything, even in the year 2016 in a highly technical field. It's
> incredibly frustrating.

I'm equally frustrated by how hard it is to get others to use standard units
instead of the French ones. There's no particular reason why 'technical
fields' should mandate use of French units: one can fly an æroplane, run power
to a lightbulb and get a man to the moon all in standard units — indeed,
that's how those things were initially done.

~~~
FabHK
Zeveb, the US customary units, "based on English measure passed by parliament
under the reign of Queen Anne in 1706" [1] are inferior to the international
SI units.

\- prefixes based on powers of 10 are better aligned with how we calculate
today, namely with base 10 numerals, and decimal fractions (unless we switch
to base 12 or base 8 numerals).

\- a single unit per physical quantity, together with prefixes, is better than
the proliferation of units in those customary systems (often with different
units of the same physical quantity in different contexts, for example length
vs area vs liquid volume vs non-liquid volume, or mechanical energy vs heat
energy).

\- the system is coherent and somewhat minimal.

\- the units are derived from the world, not from the length of some king's
feet or arms or what have you. Of course, that's a somewhat subjective
benefit.

At any rate: the original metre was 1/10,000,000 the distance from equator to
pole (that's why 90*60=5400 nautical miles = 10,000 km, approximately). The
original kilogram ("grave") was the mass of 1 dm^3 of water.

Of course, one can fly an aeroplane or get a man to the moon without SI units.
One can also do it without GPS and without computers and without internet and
without antibiotics and without all the other achievements of civilisation.
But why would one?

[1]
[https://en.wikipedia.org/wiki/International_System_of_Units#...](https://en.wikipedia.org/wiki/International_System_of_Units#United_States)

~~~
zeveb
> Zeveb, the US customary units, "based on English measure passed by
> parliament under the reign of Queen Anne in 1706" [1] are inferior to the
> international SI units.

FabHK, no, French units are inferior to the standard units:

\- 2 and 5 are poor factors; 2, 3, 6 & 8 are superior. We _ought_ to switch to
base 12: among other things, ⅓ is not a non-terminating duodecimal.

\- It is better to have multiple units for multiple purposes: anyone measuring
interstellar distances in inches or metres rather than in parsecs or
lightyears is, simply, wrong. One always has the freedom (and indeed, the
professional obligation) to use only one unit where it matters (e.g. anyone
measuring bread pans in fractions of a mile or metre is, again, simply wrong.

\- The system is scaled to human beings, and eschews superficial minimality
(BTW: steres and hectares). There are many useful units at human scale, with a
few units where needed outside that scale (there's not really much need for a
lot outside of human scale).

The units are derived from the world: the nautical mile is equal to one minute
of latitude (that's 1/60th of 1/360th); a pint is a pound of water.

\- The units are useful for manipulating concrete quantities. Half a volume of
liquid is itself a useful measure, as is double (it goes mouthful → jigger →
jack → gill → cup → pint → quart → pottle → gallon and so on, doubling all the
way up until a tun). As a computer guy, it's pretty awesome to see 64, 128 &
1,024 in my unit quantities.

As I note elsewhere, I'm in support of rationalisation of the system: history
has not been kind (c.f. rulers who kept the tax per unit the same, but
decreased the size of the unit). I think that there's definitely improvement
to be made.

But throwing it all out and adopting a decimal system goes in exactly the
_wrong_ direction.

~~~
FabHK
I enjoy the discussion, and agree that base 10 is suboptimal. Base 8, 12, or
16 would be preferable (8, 16 due to affinity to the binary system; 12 due to
the factors). However, we are stuck with 10 for now. (Surely there's an
argument against God here.)

If we lived in a base 8 or base 12 world, a radically rationalised version of
the customary royal measures based on doubling or factors 8 or 12 might be
preferable. But we are not.

> It is better to have multiple units for multiple purposes.

Why?

Differences in scale are easily accounted for with the prefixes:

mili, micro, nano, pico, femto, atto takes you down to 10^-18; with zepto and
yocto you get to 10^-24.

kilo, mega, giga, tera, peta, exa takes you up to 10^18; with zetta and yotta
you get to get to 10^24.

------
464192002d7fe1c
I can highly recommend the Mayday (Air Crash Investigation/Air Emergency/Air
Disasters/whatever its called this week) episode that deals with this,
[https://youtu.be/Bct1mWUp8to](https://youtu.be/Bct1mWUp8to), and the show in
general.

~~~
JamilD
I've watched this show since I was a kid — I think it's one of the reasons I
went into engineering. It makes you think about the different reasons that air
accidents happen, and illustrates that there's almost never a single
attributable cause.

What seems initially just like pilot error may also be due also to workplace
conditions, bad training, a lack of communication, or fatigue — a chain of
events and circumstances that culminates in the accident. It's fascinating.

~~~
464192002d7fe1c
I think the very cool thing with this show is that it really illustrates how
crashes are virtually never the byproduct of a single failure.

The most fascinating ones to me are the ones where there is a completely
survivable mechanical failure, combined with human failures that lead to
crashes. The one that comes to mind there is the plane where the engine was
leaking fuel, so the tanks were not equal so the pilots engaged the cross-feed
valve, causing _BOTH_ tanks to drain leading to an out-of-fuel situation. If
they hadn't done that, they could have easily made it to their ETOPS airport
with minimal issues.

Also, that show makes me sound smarter than I am. I've had conversations with
pilots, who will ask if I'm a pilot. Its great fun for parties when you run
into pilots (GA and commercial).

~~~
sitharus
You're thinking of
[https://en.m.wikipedia.org/wiki/Air_Transat_Flight_236](https://en.m.wikipedia.org/wiki/Air_Transat_Flight_236),
another Canadian flight.

In this case the pilots followed standard procedure for a fuel imbalance,
which is the alert they got.

~~~
464192002d7fe1c
The fuel imbalance check-sheet also points out to make sure that the fuel
imbalance isn't the result of a leak, and they did (somewhat -- it was dark
outside) try to check for a leak.

They could also have looked at the rate of fuel consumption across both tanks
to determine that the fuel consumption on the right tank was way higher than
the engine could consume, but that was not SOP at the time (it is now, and the
A330 [and probably other planes] now compute that information and alarm on
it).

Its all layers, planes, with minimal exception, really don't crash from a
single failure.

------
jbarham
Even better:
[https://en.wikipedia.org/wiki/Air_Transat_Flight_236](https://en.wikipedia.org/wiki/Air_Transat_Flight_236)

~~~
david-given
I remember seeing an entertainingly bad TV movie of a very similar incident. I
_think_ it was this one, not the Gimli incident.

But we learnt about the Gimli Glider in my university computer risks course.
It was a masterful piece of flying (and you'll note that most people who've
tried to reproduce it in simulators fail).

Sobering reading:

[https://en.wikipedia.org/wiki/List_of_airline_flights_that_r...](https://en.wikipedia.org/wiki/List_of_airline_flights_that_required_gliding)

There's a lot of flights there with casualties (including one in 2005 where a
pressurisation failure caused the crew to pass out; the autopilot flew the
plane to Greece where it entered a holding pattern until it ran out of fuel;
interceptors spotted a flight attendant trying to land the plane with portable
air equipment, but he didn't make it. No survivors). Airliners don't really
glide well.

~~~
rpeden
Many airliners glide quite well - they can glide quite a bit further from a
given altitude than can general aviation aircraft that are (probably) more
likely to run into a scenario where they'll need to glide. Air Transat 236
managed to glide 120km and land safely after running out of fuel.

The Helios flight in 2005 was unfortunate. The flight attendant trying to
control it had _some_ pilot training, but not enough to handle an out-of-fuel
airliner at relatively low altitude.

------
qwertyuiop924
Ah. I read about this in Uncle John's Bathroom Reader (which is an excellent
set of books for anyone who is compulsively knowledgable, by the way)

It's a fascinating case study in failure recovery in the worst possible
scenerios, and how systems fail to begin with.

...Come to think of it, those are all subjects Cantrill likes to talk about.
If you like playing Bryan Cantrill Bingo, I think this might make its way onto
your scorecard soon...

------
nnx
A similar incident happened on Air Transat 236. Pilot had to glide further,
about 120km over the Atlantic, before landing on an emergency landing strip in
the Azores.

[https://en.m.wikipedia.org/wiki/Air_Transat_Flight_236](https://en.m.wikipedia.org/wiki/Air_Transat_Flight_236)

------
pavel_lishin
> _Following the successful appeal against their suspensions, Pearson and
> Quintal were assigned as crew members aboard another Air Canada flight. As
> they boarded the aircraft, they realized that airplane was the same one
> involved in the Gimli incident._

That's great, but I wonder how big of a coincidence this is - how many
aircraft did Air Canada have, especially running on presumably the same leg
that Pearson and Quintal would have been running?

~~~
blakeyrat
Seems like the plane did a pretty good job the first time around, I'd feel a
lot better flying on that particular aircraft if I were them.

~~~
rpeden
And Air Canada kept it in service until 2008, so it kept on doing a good job
for a long time afterward.

------
mrfusion
Interesting, a modern glider can have a glide ratio of 60! A flying squirrel,
2!

[https://en.m.wikipedia.org/wiki/Lift-to-
drag_ratio](https://en.m.wikipedia.org/wiki/Lift-to-drag_ratio)

~~~
maxerickson
To be fair, modern gliders are bad at climbing trees.

------
lucio
[https://www.youtube.com/watch?v=Bct1mWUp8to](https://www.youtube.com/watch?v=Bct1mWUp8to)

MAYDAY Air Crash Investigation S05E02 Gimli Glider Air Canada Flight 143

------
DuskStar
"The Crash of Flight 232" is also really interesting. In some ways it's the
opposite of the Gimli Glider in that 2/3 engines were still functioning fine,
but total hydraulic loss meant that there was no elevator/rudder/aileron/flaps
control.

[http://clear-prop.org/aviation/haynes.html](http://clear-
prop.org/aviation/haynes.html)

------
daemonhunter
Interesting, Ram Air Turbine -
[https://en.wikipedia.org/wiki/Ram_air_turbine](https://en.wikipedia.org/wiki/Ram_air_turbine)

------
rpeden
I remember reading about this in Reader's Digest back in the 80s, or possibly
early 90s.

One of the passengers mentioned that during the last-minute sideslip
manoeuvre, he could almost tell what clubs the golfers on the course below
them were using. :)

~~~
webtechgal
>I remember reading about this in Reader's Digest...

Yes, that is where I had first read about it too. Don't remember exactly, but
probably under the section called Drama in Real Life.

------
RichardCA
Not sure if anyone's posted this yet.
[https://www.youtube.com/watch?v=sbE1S-i_gz4](https://www.youtube.com/watch?v=sbE1S-i_gz4)

------
gregmac
I just watched this a couple days ago on Today I Found Out:
[https://youtu.be/snVifFDoAG8](https://youtu.be/snVifFDoAG8) (9 minutes)

------
vatotemking
Those 2 kids on bicycles would surely have a helluva story to tell.

------
khazhou
I can honestly say that after spending the whole day worried about some
presentations I have to do this week, reading this makes me believe I can do
anything!

------
homero
Captain Pearson was an experienced glider pilot, so he was familiar with
flying techniques almost never used in commercial flight.

------
cpncrunch
I would recommend reading "Freefall" by William and Marilyn Hoffer, which is a
great account of this event.

------
edem
They can understand now the pain of working with fragmented standards (I look
at you Unicode and friends).

------
collinmanderson
I'm amazed that the plane was flown for another 25 years after the incident!

------
j1vms
Pearson and Sully would certainly share some interesting words, were they to
ever meet.

~~~
coldcode
Both had the right training and knowledge, Pearson was a glider pilot and
Sully taught water landings among other things. But any landing everyone walks
away from (or swims) alive is a good landing.

~~~
FabHK
And it's a very good landing if you can re-use the plane.

------
jv22222
Why isn't this Bruce Willis movie yet? ;)

------
edblarney
It's hard to believe that there is not training for a situation in which all
engines are out. Heyzeus, just a little bit of knowledge (i.e. glide ratio,
etc.) might save a lot of lives.

