As you’ve surely heard by now, on christmas day, some idiot attempted to
blow up an airplane by stuffing his underwear full of explosives and then
lighting his crotch on fire. There’s been a ton of coverage of this – most of
which takes the form of people running around wetting their pants in terror.
One thing which I’ve noticed, though, is that one aspect of this whole mess
ties in to one of my personal obsessions: scale. We humans are really,
really lousy at dealing with big numbers. We just absolutely
have a piss-poor ability to really comprehend numbers, or to take what we
know, and put it together in a quantitative way.
The context in which this comes up is in many articles written by
people criticizing the pants-wetters. The point that they’re trying to
make is that airport security is actually pretty damned good. When
you consider the number of flights, and the number of people on each flight,
and then put the number of terrorists who’ve managed to get onto a plane
and try something – successful or not – the number who get through are
amazingly small. For example, here’s one of my favorite ranters,
And the second part of the deal is that there aren’t that many
people trying. Even if you assume that for every one attempt that makes the
news, there are ten attempts kept secret, which is a wildly unlikely ratio in
a world where everyone’s carrying six cameras and wants to be on teevee?
That’s still less that 50 attempts on tens of thousands of flights over nearly
a decade. There simply aren’t that many people trying to blow up planes.
His argument is perfectly good. He’s right that the new airport security
measures are aimed at making you think that they’re doing more to
protect you than they used to, rather than actually doing more. But
ten of thousands of flights over the last decade? Ummm…. No.
Tens of thousands seems like a lot. But it’s so far off
that it’s laughable. It’s off by more than 4 orders of magnitude. It’s
smaller than the square root of the actual number of flights.
Let’s take one busy airport: Newark Airport in NJ. Newark is in full operation
for about 14 hours per day. Based on my time watching planes take off and
land there, I’d guess that they average at least one takeoff every three
minutes. But let’s guess that I’m wrong, and double the time between
takeoffs, assuming one every 6 minutes. That’s 10 flights per hour,
which adds up to about 140 flights per day. That’s definitely way
to small – but it adds up to well over 50,000 flights per day.
And that estimate turns out to be rank garbage. Looking up official
information, there were over 225,000 takeoffs at Newark in 2007 – which is a
significant reduction over previous years. So even biasing towards
the low side, Newark airport alone had well over 2 million flights
take off in the last decade.
According to the FAA, there were about 37,000 commercial flights per day
in 2008 – for a total of over 13 million commercial flights per year.
And that’s a dramatic decrease compared to a few years earlier, before
high fuel prices drove many airlines out of business, and forced others to reduce
All of us who live in metropolitan areas see ton of airplanes taking off and
landing every day. But we’ve got absolutely no intuitive understanding of just
what that actually means. I constantly rant about how piss-poor we are at
understanding scale, but I was seriously surprised by the number of flights per day
around NYC. Once we get beyond numbers that we can easily count to, our
intuitions about numbers are just a total disaster. We just don’t really
understand scale; we don’t understand how big numbers add up.
And on the topic of airport security: put the numbers into context, and you’ll realize
that all of the panic over terrorism on airplanes is really amazingly overblown. The chances of being hurt by someone who got past airport security, even without things
like the full-body scanners being deployed after this latest panic, are smaller than dying
in your dentist’s office from an anaesthesia error. And how often does anyone worry about that?