Air travel is growing in popularity across the world, and the global aviation system is undergoing projects big and small to keep up.

“We’re forecasting that traffic will double in the next 17 years,” said Angela Gittens, director general for Airports Council International (A.C.I. World). “Millions more people will be traveling.”

And those people, she said, won’t just be in places where flying is already popular. “An emerging economy now will be an advanced economy later,” Ms. Gittens said.

New and expanded airports are needed to meet that demand. Istanbul, for example, has already begun opening its new airport in phases that will eventually be able to accommodate hundreds of millions of travelers a year. When it is completed, it will be the world’s largest.