"To us and our people, it's extremely significant, " said Shane Cordes, CEO of Midwest Air Traffic Control Service, which provides controllers to towers in about 23 states in the East, Northeast, Great Lakes and central regions of the United States.

CNN: FAA begins process to close 168 towers on April 1

Like many projects in air-travel modernization, there's a chicken-and-egg question: Should airlines spend money on equipment before air-traffic control agencies prove they can work with it, or should air-traffic control service providers spend first and then wait for airlines to catch up?

WSJ: Texting While Flying: Help for Pilots