I noticed airlines in Airline Mogul seem to get very large, very quickly. So I decided to compare the biggest airlines in the real world, to world 6. I would like to first note that this game has been going on for less than 10 years, the real airlines have had much longer than us to build up. There are some interesting statistics.
The largest airline by passengers (in world 6), carries 1,544,496 daily. This equates to 563,560,000 passengers per year.
When we look at real stats, the biggest airlines (in 2007) are:
Southwest Airlines: 101,911,000
American Airlines: 98,162,000
Delta Air Lines: 72,900,000
The data, which goes back 3 years shows Southwest has been increasing, and American/Delta have been decreasing slightly. Despite this, I doubt any would have ever been near the 500,000,000 mark.
As another example, to have 200,000,000 passengers per year (far higher than any present real world airline), you need about 548,000 daily passengers. 7 airlines fit into this category.
To have 100,000,000 passengers per year (making you tie with our world's largest, Southwest), you need about 274,000 daily passengers. 22 Airlines in world 6 fit into this category.
Another intesting statistic is that the 300 airlines listed as tranporting passengers, transport over 26,000,000 passengers per day, or 9.49 billion passengers per year.
Finally, the 344 airlines (many of which are in debt, bringing down the value) are worth 2.2 trillion euros.