Friday, August 1, 2014

Air Safety: A Reassurance, Hopefully

Photos of the MH17 wreckage near the town of Shaktarsk in rebel-held eastern Ukraine, on July 17, 2014. All photos by DOMINIQUE FAGET/AFP/Getty Images

Blogger’s note: I have found a 51-second video clip of the MH17 crash scroll down below. WARNING: It contains graphic images that may be disturbing. View it at your own discretion.

I am aware that many people are very much alarmed at the spate of aviation disasters and I have read too that Malaysia Airlines saw many cancellations. Like everybody else, I too wonder just how safe it is to fly. Of course, if you are not intending to fly any time soon – you should feel very safe!
There’s another write-up – an Alison Gee article dated July 25, 2014 in BBC News magazine – which I came across that looks at air safety. I can agree to the fact that statistics do provide some degree of comfort.

Harro Ranter, director of the Aviation Safety Network which catalogues plane crashes, says clusters of accidents are not unusual. Analyzing the number and frequency of fatal crashes of aircraft capable of carrying 14 or more passengers since 1990, he finds 45 dates when there have been two or more crashes (excluding collisions).

Ranter says it is more common for an accident to happen just one day after another crash than two, three or more days later. In fact, there were 105 cases where there have been accidents on consecutive days!
Arnold Barnett, a Professor of Statistics at the Massachusetts Institute of Technology, USA – while not discounting this phenomenon as essentially resulting from coincidence – also draws attention to the theory of Poisson distribution, which implies that short intervals between crashes are actually more probable than long ones.
Barnett’s illustration: Suppose that there is an average of one fatal accident per year, meaning that the chance of a crash on any given day is one in 365. If there is a crash on August 01, the chance that the next crash occurs one day later on August 02 is 1/365. But the chance the next crash is on August 03 is (364/365) x (1/365), because the next crash occurs on August 03 only if there is no crash on August 02.
Barnett says the conclusion follows relentlessly from the laws of probability. I suppose you can consider this to be an assurance that we should not expect the coming months to have an unusually high number of accidents! Improbably so!

Barnett points out that during the 3 months of April, May and June this year, there were no fatal accidents at all involving scheduled commercial flights.
He is right when he says that it is hard to imagine that the skill that led to this marvellous record somehow disappeared in July! He even calculates that in developed countries the chance of dying is about one in 25 million per flight. Even in the world's least developed countries, the chance of dying on a flight is about one in 750,000.

The world has already witnessed three fatal crashes in just eight days in July (17th, 23th and 24th). And David Spiegelhalter, Professor for the Public Understanding of Risk at Cambridge University, UK has worked out that there is about a six in 10 chance that we should see such a large cluster during a 10-year period, and he calculates "the most likely maximum number of crashes of commercial planes with over 18 passengers in any eight-day window over 10 years is exactly three".

So, folks, we can be rest assured that flying is safe. Only if you believe the statisticians, that is!
And here’s the said video:

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