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"Too Many Sheep"
Or, What Air Travel has in Common(s) with British Sheep Farming Villages of 700 Years Ago
By Paul Cox September 1, 2004

(I wrote this article prior to the attacks of September 11, 2001. Plainly, they set back aviation and air travel in this nation for some time; however, I think two things are obvious. 1- Even if traffic drops back to where it was 3 or 4 years ago, that is still a level that gave us plenty of air traffic delays; and 2- Sooner or later air travel will pick back up and continue its climb, and we will be faced with these issues.)

Flight delays in the US continue to bedevil the airlines and the FAA. The summers of 2001 and 2002 saw some improvement from the horrible delays in summer 2000, but it will likely prove to be short-lived and the overall trend of increasing delays will increase.

Air traffic control (ATC) is often blamed for delays, yet ATC actually has little to do with their cause. In fact, nearly all of the stakeholders in aviation (primarily the FAA, the airlines, and the flying public) often ignore the true cause of air traffic delays.

Collectively, we must come to an understanding that these flight delays are primarily due to overloaded, overscheduled airports.

Obviously, if the particular airport you want to fly into has too many airplanes trying to arrive at once, you're going to be delayed. But aircraft in holding take up large hunks of airspace, which can lead to delays at nearby airports (while those planes deviate around the ones holding!)

Ironically, ATC and more regulation are probably the best solution for delays.

ATC can actually handle more aircraft-while enroute, not holding in the air- for nearly all airports. It's a big sky. Delays come when there is no room on the ground at the airport for airplanes to land. As John Carr, president of the National Air Traffic Controllers Association, points out, "our problem is nothing that 50 miles of runway at the nation's 25 busiest airports wouldn't solve."

Relying on building new runways will not represent a total solution to the problem. We will run out of politically tolerable places to put runways, and sooner or later we will be "built out".

View, for example, the huge fights to add runways in Boston, Seattle, and Chicago. Sooner or later, there will simply be no real estate close enough and inexpensive enough (in both dollars and political capital) that we can add runways to; at that point, we will have reached maximum capacity.

Tragedy of the Commons

"The tragedy of the commons" is an economic theory, proven true by many observations. It basically states that when users have joint ownership of a common resource, they often have no incentive to invest in the future good health of the resource.

In fact, users will exploit and destroy such a resource as quickly as possible.

The classic example is English sheep farmers in the 14th century. The farmers used a "commons", a large field for grazing, which was jointly owned by their entire village.

Imagine a farmer, living in such a village. It is growing in population. The commons used to only have a couple dozen sheep on it, but now it's got 100 sheep there. This is maximum capacity.

Any more sheep and the grass doesn't have time to recover. The sheep also trample areas down when they walk, they poop, and that takes a while to break down. In short, the environment is at its capacity. With 100, the field can recover; this is the most it can sustain.

Our farmer friend has 10 sheep out of the 100 on the commons. This means each sheep he owns represents 1% of the overall herd. However, to him, each sheep is 10% of his worth, so to him each one is pretty darned important.

He decides to make more money and add two sheep. With two more sheep, he has a total of 12. He has effectively increased his wealth 20%.

Unfortunately, now the overall herd is over the capacity of the commons. This affects every sheep in the herd. However, since the overall herd only increased 2%, the effect is small and hard to notice. Basically, it negatively affects each shepherd about 2%- including our farmer.

So he gained 20%, but lost 2%, for a net gain is 18%.

Naturally, our farmer thinks he has made out. Sure, the commons can't quite sustain 102 healthy sheep, but what does he care- his wealth has just skyrocketed, and he can now afford some new thatch for his roof!

His fellow farmers notice his higher station in life; being only human, they decide to increase their own holdings and wealth as well. So they start increasing the size of their personal flocks.

As the commons becomes overloaded, all the farmers see a reduction in their wealth- their flocks get more and more sickly. However, when each farmer considers his own personal situation, it makes sense for him to continue adding more sheep.

As more and more farmers add sheep, the overall impact starts getting worse. If 10 farmers add two sheep, the overall impact to the commons is 20% degradation, even though each individual farmer thinks he's "only" adding 2% to the problem.

Eventually, what happens is everyone tries to keep adding sheep to improve their own situation; individually, they seem to gain, but overall, the commons is rapidly overloaded and the population experiences a "crash", a breakdown of the system. Sheep get sick and die, and instead of 100 relatively healthy sheep, there are 150 sickly ones.


The point of this analogy is to illustrate what happens when a jointly owned resource (the commons) hits or approaches its maximum carrying capacity.

In today's world, we have almost exactly the same situation when it comes to air traffic. The "commons" is the airport, or more exactly, the unfettered access to an airport's runways. Most airports are run with little or no limits upon how many flights can be scheduled to land each hour by the individual airlines.

The airlines make money by having more flights; the more passengers they fly, the higher their profits. Naturally, they all want to keep adding flights.

Once an airport starts getting overloaded, the delays from each individual airline's addition is spread among all the airlines, so the individual airline adding a flight doesn't "feel the pain".

Say an airport that can handle 45 flights an hour during good weather. There's an airline that already has 4 aircraft in a particular hour. They decide to add a flight to that hour.

It doesn't matter very much to them if the carrying capacity of any particular airport is only 45 flights an hour; they are going to increase their number of flights that hour (and hence, profits) by 25%. The delay from having too many airplanes in that hour is spread amongst all the users, however, so the individual airline winds up getting everyone else to pay the cost of their increased profits.

If 4 other airlines do the same thing, the overall effectiveness of the airport that hour might drop by 10 to 12 percent; but they're each increasing their profits 25%, so they don't care.

Our hour is now overscheduled- there are 50 flights trying to land when the airport can only handle 45. The "true" max arrival rate allows for one airplane every one minute and twenty seconds; since there are five extra, the last airplane is going to be delayed almost 7 minutes total.

The problem, of course, is that this delay must come at someone's expense- and the delays continue into the next hour, and the next, and the next, to the point where they continually build so long as the airport is at or over its maximum arrival rate.

Now imagine our airport is having bad weather, and only 30 planes can land per hour. There are 20 extra planes in the first hour; they take up the first 20 slots of the next hour, which only leaves 10 slots... for the NEXT 50 airplanes. This delays everyone and pushes 40 more airplanes into the third hour's slots... and so on, and so on, and so on, until there's a gap in the schedule that allows the airport to catch up.

What we've seen in the growth of air travel reflects that. No single airline pays the entire price of adding flights (and increasing congestion and delays) to an airport; instead, the pain of the delays is spread amongst all the users of that airport.

We might wish to ignore the facts but they are simple. We cannot continue to allow unfettered, unregulated access to airports. As long as we do that, airlines will add more flights. The end result of this, of course, is complete system gridlock.

Before you pooh-pooh this notion, view the example provided by LaGuardia in New York City. The delays there were reaching epic proportions, and affecting air traffic all up and down the East Coast.

The FAA (finally) stepped in and restricted the number of landing slots available in each hour, and the delays have effectively disappeared.

To Close

Just like those sheep, hundreds of years ago, sooner or later we see a situation where the "commons" (the airports) are so jammed up that everything slows to a crawl- yet each airline tries to improve their own situation by continually adding flights.

There are some simple solutions, and sooner or later we're going to have to put most or all of these into place. Exactly which ones and in what proportion is a question to be determined by political decision-making, but something must inevitably be done.

First, we must ensure that we have as many runways as we (as a people) can stand. Since numbers of runways effectively limit the ultimate number of flights that can arrive, we should ensure that we have reached our limit in how many runways/airports we are willing to accept.

Second, we must ensure that we are using those runways as efficiently as possible. The first part of this is to maximize the efficiency of the ATC system; this is an ongoing project for the FAA, but the gains possible are limited by ultimate safety requirements (you can only allow planes to get so close before they start hitting each other).

The next phase in using runways more efficiently is to increase the numbers of passengers on each aircraft. The most obvious way to do this is to use larger aircraft; ways to encourage airlines to do this would be to charge a flat-rate landing fee, which means per passenger small planes pay a higher fee than larger ones.

Third, we must start regulating how many aircraft are scheduled into an airport. There are several ways to accomplish this, and none of them are easy or popular with the airlines. This limit must be at or below the carrying capacity of the airport.

These are not going to be easy decisions to make. There will be tremendous infighting, with each party involved trying to ensure that their interests are protected as much as possible.

Calls for even less government involvement are completely misguided. Unregulated access to the common resource is why we are seeing delays grow.

Suggestions that the ATC system be privatized in the name of "making it more efficient" are a last-ditch grab for profits and control of the system. If the airlines (i.e., business) can gain control of the ATC system, they think they can stave off the complete overload long enough to squeeze out more profits.

It should be obvious to anyone who has flown recently that we cannot have an unlimited supply of flights. We are already at or nearing our maximum capacity at many airports.

What everyone in the process needs to do is sit back and recognize that they ARE a part of the problem; and thus, they ARE a part of the solution.

Copyright © 2004 by Paul Cox

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