I flew to Chicago via London through United Airlines, and they (along with a few other carriers) have a feature on their website that allows you to track where your plane is coming from. Using this, we can go into the past and see the past 10-20 routes that our plane has been on. This let's us begin to get a glimpse into why certain planes fly certain routes. While my plane was a Boeing 767-300 it is also known to fly from Chicago to Washington DC (and to a large host of other domestic airports). By using data collected from this service, I began to seek if could find some logic in how planes are assigned to different routes.
While it is obvious that certain planes fly different routes as that is what they were designed for (the reason why a Trans-Pacific airplane is much larger than one flying between London and Paris), what I seeked to find an answer to is how planes of a certain type are assigned to different routes. Was my London to Chicago flight one in which always flew the same path, or was it also switched out to shorter domestic runs?
This is a question I've been wondering for a while. Two years ago I discovered this feature while waiting on a delayed plane on a Vancouver – Chicago flight and hand drew a small map over everywhere my plane had been before.
For quite some time I've seen airplane paths or connections between cities on the earth mapped beautifully through great circles. A great circle is essentially the the shortest path between two points on the surface of a sphere. It's the path in which airlines fly to get from points A – B, and the reason why my flight from London to Chicago takes me over Greenland, and not the Mid-Atlantic.
While mapping the routes from A – B is relatively simple in R, through the use of a simple line, two points (expressed as latitude and longitude), and R's Maps library – using a great circle provides a much more accurate (and beautiful) way of representing global travel.
Without going into too much detail, there are a number of incredibly detail tutorials available for using Great Circles in R through the Geosphere library. Flowing Data's tutorial provides an excellent starting point.
The end results are rather minimal,and more data will be needed to get a better answer. Unfortunately FlightAware's API and United's "where is my plane coming from?" features are limited in the amount of data that can be collected. For now the answer likely has much more to do with plane availability, maintenance, and life, rather than a simple single-path only answer.