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The Flight Network
4000 airports served by commercial airlines
Served by average of 4 airlines, connect to 8 others
Weighted by # of departures, 22 airlines, 64 destinations
Dominated by large airports
- largest 1% (>4000 flights/day) have 40% of departures
- largest 10% (>250 flights/day) have 85% of departures
- reflects airlines’ hub-and-spoke system
Shortest path averages 3.5 in US, 5 worldwide (uniformly weighted)
Diameter > 20
30,000,000 scheduled commercial flights per year – 1 per second
4000 – 10,000 planes in air, mostly large jets
700,000 passengers in the air
50% of flights within US and Canada
Notes:
There are more than 4000 airports served by commercial airlines worldwide. Averaged uniformly, each airport has an outgoing degree of 8 (it has flights to 8 other airports), and is served by 4 airlines. However large airports dominate the system: re-weighted by their number of departures, airports average degree 64. This reflects the hub-and-spoke system used by many airlines, wherein for a given airline one to four airports account for half of their departures. Despite the high connectivity amongst the major airports, the shortest path between two airports chosen uniformly averages 3.5 flights in the United States and 5 worldwide. Amazingly, the graph diameter is often as high as 20: there are airports that can take 20 flights minimum to get between, over 4 days (typically this will be a small airport in Alaska or Canada to another small airport in Africa or Indonesia).
Commercial airliners take off about once per second worldwide, and most are large jets more than half full, resulting in close to a million people in the air at times. The United States and Canada heavily dominate air travel in terms of numbers of flights, though deregulation in Europe has led to a great increase in air travel there over recent years.