That is why almost every important airport is now dominated by a single airline.
The purpose is to make travelers believe they are making the entire journey on a single airline, a distinct marketing advantage.
If you want to buy 30 days at a time, it's $30 for a single airline or $40 for all airlines with no automatic renewal.
It concluded in 1932, and recommended that a single, large national airline be established.
Together, the airlines carry 80 million passengers a year to 339 destinations in 71 countries - more traffic than any single airline.
Targeted sales also helped Delta carry 97.3 million passengers last year, an industry record for a single airline.
"It does seem that you're probably going to have a single airline," he said.
"I don't think China has a single airline with the financial clout to bring an order like this to fruition."
Instead, he said, they feature itineraries from a single airline.
The dominance of airports by a single airline should be limited.
