It's been a nightmare for travellers flying through Canada's busiest airport, with long lines, flight delays and cancellations becoming the norm, and aviation experts predict that these problems are only going to get worse before they improve.

Duncan Dee, former chief operating officer for Air Canada, says much of these delays stem from staffing levels at customs and immigration desks at Toronto Pearson International Airport inadequately equipped to deal with the surge in passenger traffic as well as the COVID-19 border measures, creating a domino effect of delays.

"Each and every one of the travellers is screened. And it's now taking four times longer than it did before the pandemic," he told CTV News on Wednesday.

Prior to the pandemic, it used to take 30 to 60 seconds to screen a passenger for customs and immigration. Today, Dee says the process takes four to five minutes, thanks in large part to the COVID-19-related screening questions through the ArriveCAN app and checking of vaccine certificates.

"You've quadrupled the amount of time it takes them to process every traveller. So unless you quadruple the number of people doing the processing, you're going to have a delay," he said.

Travellers unfamiliar with the ArriveCAN system may not have filled out the form on the app properly. They may have a proof of vaccination that isn't in English or French, or the type of vaccine may be one that isn't distributed in Canada, such as the Russian Sputnik V vaccine. Some travellers may even be randomly selected to undergo a COVID-19 test upon arrival.

All of this adds another "level of complexity" for Canadian Border Services Agency (CBSA) officers, Dee says.

"The CBSA officers are some of the best around. These folks do a really great job and normally they work extremely quickly, but you've put them in a position where they're trying to enforce mandates that are completely impossible enforce in the timeframe that they've got," he said.

The delays and long lines at the customs hall in turn create a knock-down effect that create more delays for incoming international travellers who haven't gotten off the plane. Dee says in order to avoid overcrowding at the terminal, incoming planes will be instructed by air traffic control to wait at the tarmac until some of the backlog at the customs line has cleared.

And even when passengers start deplaning, they may only let 10 to 50 passengers per half hour get off the plane at a time in order to avoid a crush at the terminal.

"If you've got 250 people on a plane, with 50 every half hour, you're suddenly counting another hour and a half before everybody is off the plane. But that's not even the end. They get to the customs and they're behind a two-hour line before they even see an officer," Dee explained.

"All of that adds up … and it's six and a half hours before they get into a taxi or their ride home and it's just not sustainable."

AIRPORT WOES EXPECTED UNTIL SEPTEMBER

With more travellers expected in July and August, Dee says the problems at Pearson are only going to get worse.

"It's a simple mathematical equation. There are 22 to 24 per cent more travelers in the months of July and August than there are in May in April and there were lineups in May and April. You could just imagine what happens when there are even more travelers in July and August," he said.

But the issues at Pearson aren't a uniquely Canadian problem. As Transport Minister Omar Alghabra has pointed out, many European airports have also been struggling with delays and long lines, sometimes stretching to outside the terminal.

In an effort to address these delays, Alghabra has said the federal government is hiring 400 new CATSA screening officers and is looking into making "more adjustments" to COVID-19 travel rules. But McGill University aviation expert John Gradek says the much of the blame lies with the airlines rather than CATSA or the CBSA.

"The root cause is that there's too many passengers coming into and out of the airports than what the capacity the airport can handle," Gradek told CTV News on Wednesday.

Some European airports, such as Amsterdam's Schiphol and London Heathrow airports, have asked airlines to cut their flights and cap the number of passengers in order to avoid overcrowding. Gradek believes similar asks need to be put to Canadian airlines.

"The airlines are hungry for money. They're hungry for revenue. So, they're going to pack on their schedules. They're going to want to have more and more passengers onto their airplanes, generate more revenue," he said. "Somebody has to step up and basically say, 'X percentage of your flights, you have to cut back.'"

Both Gradek and Dee expect the delays to plague Pearson and other airports around the world until September, after the end of the summer travel season.

"The airlines have yet to see the best passenger numbers. The airports have yet to see the worst of their delays," Gradek said.