Why America’s Busiest Airport Is Still Running On Air Traffic Software Built Before The iPhone Existed

Source Domain: simpleflying.com

There are various ways to grade how “busy” an airport is, and this impacts the rankings. The busiest airport is typically regarded to be Hartsfield-Jackson Atlanta International Airport as it has the most passengers annually (106.3 million in 2025). However, Chicago O’Hare also lays claim to being the busiest airport in the United States by number of takeoffs and landings. In 2025, O’Hare had 857,392 aircraft movements, placing it ahead of Atlanta’s 805,268 movements.

Regardless, both of these airports’ air traffic control (ATC) systems use an assortment of software dating back to before the iPhone. While that may sound dramatic, the devil is in the details. Overall, the US’ ATC is made up of a network of systems that are both older and more modern than many people may expect. The system is also in transition to the much more modern Next Generation Air Transportation System (NextGen), which is expected to continue rolling out into the 2030s.

If It Ain’t Broke, Don’t Fix It

Credit: NATS

The world is full of examples of old technology developed many years ago. New systems may have been developed, but the old systems were never replaced. Often, upgrades are layered on top, but the underlying system remains the same legacy system. Often, it works well enough and avoids the gargantuan task of replacing the old system. This is true of many banks’ software. Sometimes, it’s just entirely infeasible to change…

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