The scene in the air traffic control tower at Dulles International Airport during a tour by The Federal Aviation Administration along with UPS and United Airlines as they gave a firsthand demonstration of the NextGen technology called Data Communications (Data Comm) on Sept. 27, 2016. (Ricky Carioti/The Washington Post)

The Federal Aviation Administration has taken another step into the 21st century, replacing an archaic system that required a pencil and paper with a digital link between pilots and the control tower.

The computer link with planes awaiting takeoff has been installed in 45 major airports — including New York’s three, all three in the Washington-region and Los Angeles— and will be added shortly in several others, including Chicago’s O’Hare International, the FAA said Tuesday.

The system in use to date has been a throwback to the days post-World War II, and it gives passengers who have wondered a glimpse into what’s going on in the cockpit as they inch along the line toward takeoff.

Here’s how it works: The airline sends the control tower a proposed flight plan for the plane that’s warming up at the gate. The captain will have picked up a copy of that as he walked on-board. In the tower, that plan prints out on an 8-by-1-inch piece of paper. On a good day, controllers in the tower give the thumbs up and the paper is stacked on a board that shows the order in which the planes will take off.

On a bad day, when the weather makes for ugly flying or something else has disrupted the system, the tower controllers have to come up with a new route to get the plane where it’s going. That new plan will pop out on another 8x1 piece of paper. The controller then reads the instructions to the waiting pilot, who writes them all down on paper. The pilot then reads them back and the tower corrects any mistakes. The pilot confirms the corrections, and the tower clears the plane to fly — although all the back and forth may have cost the pilot his place in line, further delaying the flight.

Shown is the Data Comm system aboard a UPS Boeing 767 during a demonstration by The Federal Aviation Administration along with UPS and United Airlines at Dulles International Airport on Sept. 27, 2016 (Ricky Carioti/The Washington Post)

With the new system, the whole business can be done with the push of a button. The airline dispatcher files the flight plan with the tower, the tower approves or revises, the flight plan pops up on a mini-screen in the cockpit, pilot reviews and approves it, plane takes off.

“This eliminates a huge amount of traffic on the radio,” said UPS pilot Gregg Kastman, who demonstrated the system in a UPS plane cockpit at Dulles International Airport on Tuesday.

The system, known as Data Comm, has been tested for more than two years at Memphis and Newark international airports. The FAA says that in return for its $741 million investment, Data Comm will allow planes to fly more direct routes, saving fuel and reducing airplane exhaust fumes. The major U.S. carriers have signed on for the program, though not all of their planes been equipped yet.

A similar system has been used by U.S. and foreign carriers for more than a decade on oceanic flights. For now, the FAA says, Data Comm will be used to speed planes as they prepare for take off. By 2019, they expect the system will be used by the 20 centers that control planes at cruising altitude.

The Data Comm system, which is being delivered two years ahead of schedule, was an early inclusion when the FAA created NextGen as an umbrella for numerous works in progress.

It’s the brand name the FAA created more than a dozen years ago as it recognized that it needed to sell Congress on funding for a grab bag of expensive new programs with the potential to dramatically change the way in which airplanes travel from place to place.

But with the massive funding for NextGen — the airlines are expected to invest billions as well — came pressure from Congress and the White House Office of Management and Budget to show meaningful results, expectations that might not have arisen for several individually-funded projects that no one outside the FAA fully understood.

One result of that pressure was that NextGen expanded like an accordion, with projects that pre-dated NextGen by several years suddenly being added to the NextGen portfolio as they neared completion, and could be pointed to as milestone of success.

For example, in 2000, IBM told the FAA that it didn’t intend to support the agency’s navigational system beyond 2010. So the FAA set out to revitalize the system with something it called En Route Automation Modernization, or ERAM.

That system, now in operation, was instigated before the term NextGen was coined, yet the FAA now says it is “the heart of the Next Generation Air Transportation System (NextGen).”

“I would argue that it isn’t really NextGen,” said a former top FAA official who asked not to be named because he still works in the aviation industry. “It really is replacing what they had in 2001. That’s sort of what they’re touting as NextGen, but all this does is, eventually, when they build NextGen, is to plug new systems into it.”

In the heyday of NextGen funding, he said the inside joke at the agency was “that someone at FAA could figure out how to modernize the cafeteria and call it NextGen to cover the cost.”