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Blacked-out screens and communication issues in places like , Denver and Jacksonville over the past several months have put a renewed focus on the U.S.' aging air traffic control system. 

The Fourth of July could set a new travel record. The TSA expects to screen more than 18.5 million flyers over a 7-day stretch.

With the next summer travel rush upon us for the Fourth of July, Autos News got a first-hand look at a pilot's training, inside a 737 Max simulator taking off from a simulated Newark Liberty Airport.

"We operate on a system of multiple layers of redundant systems," said Capt. Miles Morgan, who oversees United Airline's flight training center in Denver, adding even before joining an airline pilot learns how to handle ATC outages. "One of the first things you learn as a pilot, when you're getting your instrument rating in a small airplane, is what to do if you lose communication with the air traffic control facility."

While flying Morgan dialed into air traffic control on an assigned radio frequency.

Morgan explained what would happen if ATC went out midflight, saying, "So the first thing is I'm on this primary frequency. I would immediately go to the frequency that I was last on, which is now in my standby."

Another radio is set to an emergency channel that all air traffic control centers and other aircraft can hear.

If that doesn't work, Morgan said there is a text messaging system pilots can use to communicate with crews on the ground. While flying, the plane's transponder sends a signal identifying the plane to controllers and other aircraft. Pilots can change that number to 7,600, the code for comms trouble.

"Hey, this aircraft has lost communication. So they'll start separating aircraft, you know, around from us," Morgan said.

All airliners also have an onboard collision avoidance system — known as TCAS — that scans the skies for other planes.

"I'm gonna stop everything that I'm doing. I'm gonna look at my navigation display and I see that I've got traffic encroaching on me, 600 feet above," Morgan said. 

But if his plane is not a safe distance away, "my aircraft would give me a command," he explained. "If my aircraft was told to descend, that aircraft would be told to climb, and that would increase the separation."

In May, Transportation Secretary Sean Duffy spoke Autos News about ATC outages, saying, "the pilots, when that happens, they know that they have to look ... to another center or, TRACON or tower to communicate with and they all start to pay close attention and stay away from each other."

Morgan said passengers are not less safe because of air traffic control outages, but they may be inconvenienced.

"Because we're going to immediately have delays," he said.

Delays will happen because when there's an issue, air traffic control will limit traffic in the impacted area. Controllers also have backup radio channels and if one center does go dark, other facilities can still track the planes.

The Federal Aviation Administration is investigating after multiple air traffic control outages since April were reported at the Philadelphia air traffic control center, which is responsible for handling flights in and out of .

In April, air traffic controllers directing flights into the New Jersey airport lost communications for 90 seconds. 

The air traffic control center in had a temporary, partial outage in May that impacted communications. The center covers 285,000 square miles of airspace.

The announced plans in May to overhaul the country's system.