CHANTILLY, Va. — Airline pilots and air traffic controllers are on schedule to switch to text communications at most of the nation’s busiest airports by the end of the year, a milestone that holds the potential to reduce delays, prevent errors and save billions of dollars in fuel cost, says the Federal Aviation Administration.

Controllers and pilots will still use their radios for quick exchanges like clearance for takeoff and in emergencies and situations where time is critical. But the nation’s air traffic system is gradually shifting to text messages for a majority of flying instructions.

That’s a big advantage, say government and industry officials, because up until now longer and more complicated instructions like a route change for pilots of planes waiting to take off are communicated verbally, with each word laboriously spelled out in the radio alphabet. For example, HARD becomes “Hotel Alpha Romeo Delta.” Pilots have to write down the directions as the controller reads them, then read them back, also spelling out each word. If there is a mistake, the controller reads the directions back to the pilot again, and so on. Even when there are no mistakes, the process can eat up valuable minutes.

If controllers want to reroute planes around a thunderstorm, they have to contact each plane by radio to relay instructions. With dozens of planes waiting, the process can take 30 minutes or longer.

With the new system, Data Comm, a controller can type a few instructions into a computer, tap a key and send the message to the flight management computers. Pilots read the information on cockpit display screens and can accept it by pushing a button.

Typing errors are always a risk with text messaging, but officials said the system has built-in safeguards that cause it to reject messages with certain errors.