tim's experiment

The launch of the consultation on the third runway was accompanied by a barrage of propaganda from the general direction of the airport, warning of the dire consequences of not providing the new runway in planty of time. The gist of this was that the present airport would be full to capacity in 2020, at which point we would presumably have to start turning people away.
Fortunately these predictions did not come from the government, which seems to be constitutionally incapable of calculating anything ten months ahead, let along ten years, and would in any case be widely disbelieved. Having been sold one white elephant in the form of the high-speed rail link the public will not, I suspect, willingly buy another one, at least from the same vendor. Anyway the airport interest is perfectly willing to pay for propaganda itself. It is not, apparently, willing to pay for the runway on the other hand. That is going on our tab. So what are we to make of these figures?

Well I for one would be happier with a range of outcomes. It is very easy to project the growth rate from the last few years and announce that in so many years something will hit a limit. The possible problems in this approach are nicely illustrated by the gentleman who pointed out a few years ago that if then current trends were followed then the entire US defence budget in 2030 would buy one aeroplane. All trends are, in a sense, temporary. And you can pick which of the past few years to start from, depending on whether you want to hit the limit early or later. This procedure is subject to gross errors because very small variations in growth rate or starting position can compound over time. So I am suspicious about that date.

A more tricky problem which has not been explored yet is that we are not talking about a new terminal (or at least we are, but the cost of that is trivial). We are talking about a new runway. Now the required terminal capacity of the airport is roughly proportionate to the number of passengers. And the required cargo handling capacity is proportionate to the amount of cargo. But the runway does not care whether the aeroplane trundling down it is large or small, empty or full. The required runway capacity is proportionate simply to the number of landings and take-offs. This is important because before we translate our projected passenger and cargo quantities into future needs for runways we need to consider whether the planes will remain the same size.

Now there are several reasons for believing that they will not. One is that aeroplanes generally have tended over the years to get bigger. Another is that if capacity is short the airlines may be persuaded to waste less of it. If you are flying to London you gfet a large aeroplane because the short ones cannot make the trip. If you are going to some city in China, on the other hand, you do not walk down a tube to a Jumbo jet. You get a bus out to some distant part of the tarmac, where you board an aeroplane which is not much bigger than the bus. The attraction of this to the airlines is that they can offer a lot of small flights every day, thereby appealing to the business traveller, who is presumed to be picky about these things and to place a high value on his time., But of course this means that the number of runway slots needed to get a particular number of people to Wuhan is about six times the number of runway slots needed to get the same group of people to London. The third reason to wonder about runway capacity is our beloved high speed rail link. This is supposed to bring most Chinese cities within a few hours travelling time from Hong Kong and while some of these claims will turn out to be exaggerated it is certainly true that lines already completed in the mainland have wiped out some short-range air routes.

So I wonder if we will need another runway. If it turns out that we don’t then you will not, needless to say, be able to ask for your money back…