Airplane Wi-Fi has been around for decades, but its reliability and speeds can vary widely depending on the airline, the route and the type and age of the aircraft.

American Airlines, United and other U.S. airlines have recently been updating their fleets to provide better Wi-Fi, and Delta has spent more than $1 billion upgrading its planes to offer free Wi-Fi to customers.

The airline uses Viasat, one of the leading providers of satellite internet, to deliver Wi-Fi on board. Viasat recently launched a new satellite with faster speeds and more capacity, which the company says should help keep up with the growing demand for the airline industry.

CNBC got an inside look at how Delta is working to upgrade over 1,200 planes by 2024.

Watch the video to learn more.