Memorial Day weekend marks the start of the airline industry's busy summer travel season and airfare expert Bob Harrell said fares are going up.

"Well, they've been going up fairly dramatically in the last six months at least," he told Yahoo Finance.

Harrell is president of Harrell Associates, a firm that tracks and benchmarks ticket prices across the industry. In normal times, business fares are four to five times more expensive than leisure fares, according to Harrell, but right now, "business travel in today's environment is nearly non existent. So the name of the game is leisure fares," he said.

Harrell's airline index tracks leisure fares across 300 domestic routes in the United States. He said the increase in fares began before Easter and continued through the end of April. "The leisure fares on a national basis went up by 7.7% which is a lot in a several week period."

That uptick was captured in the April consumer price index (CPI), which showed inflation running up 4.2% driven by increases, "for shelter, airline fares, recreation, motor vehicle insurance, and household furnishings," according to the U.S. Bureau of Labor Statistics.

'Travel without quarantine'

According to the Transportation Security Administration (TSA), 1.7 million passengers moved through TSA check points on May 9, the largest number in more than a year. In 2019 that number was 2.4 million. Harrell said increased demand is putting pressure on airlines to charge more for tickets as passengers return. "Airfares will definitely be returning to closer to normal later this year," he predicted.

"We believe the Biden administration needs to make a decision about international travel within the next week to 10 days," Cowen Equity Research analyst Helane Becker wrote in a note to her clients May 11th.

The airlines want their lucrative transatlantic European routes reopened as Americans plan their summer travel. CEOs from major carriers in the U.S. and UK sent a letter this week to airline regulators in both countries calling for a summit to restart air service between the two continents.

"Nobody wants to go to Europe to stay in their hotel room for a week or be under quarantine," Harrell said.

Becker told her clients, "Even though we believe vaccinated people should be able to travel without quarantine, Europe remains mostly closed. Greece, Iceland and Croatia are open to U.S. citizens. We thought the UK would open to U.S. citizens on May 17, but it was not one of the countries on the UK's 'green' list, which is disappointing."