MONTREAL — A majority of domestic flights to Canada’s busiest airports were delayed or cancelled over the past week as the effects of an overloaded international network continue to ripple across the country.

Some 54 per cent of flights to the four largest airports were bumped off schedule in the seven days between June 22 and 28, according to analytics firm Data Wazo.

More than 44 per cent of the 4,815 flights were delayed while 8.5 per cent were scrapped altogether.

Toronto’s Pearson airport topped the list, with 51 per cent of flights delayed — more than 700 — and 12 per cent cancelled. Montreal was runner-up at 43 per cent delayed and 15 per cent cancelled. The other two airports were Vancouver and Calgary.

Airlines and the federal government have been scrambling to respond to scenes of endless lines, flight disruptions, lost luggage and daily turmoil at airports — particularly at Pearson — a problem the aviation industry has blamed on a shortage of federal security and customs officers at the Canada Border Services Agency (CBSA) and the Canadian Air Transport Security Authority (CATSA).

John Gradek, head of McGill University’s aviation management program, says carriers have used Ottawa as a “scapegoat” while scheduling more flights than they have staff or planes to provide, resulting in delays and cancellations.

“The airlines have lost some of their mojo,” he said. “The government has reacted and has pumped up the resources, and we’ve still got chaos.”

Canada’s airport security agency has hired more than 900 screeners since April, though many remain in training. Ottawa also suspended randomized COVID-19 testing of vaccinated passengers on June 11 through at least Thursday following sector demands to process international travellers more quickly.

Passengers and federally regulated transport workers are no longer required to be fully vaccinated to board a plane or train in Canada or come to work.

Ray Harris, who heads the Fredericton-based Data Wazo, said his figures show flight disruptions have not improved in June — despite the paused tests and back-to-work staff — at the outset of peak travel season.

“That didn’t really move the needle in any direction,” he said in an interview. “Or maybe it did speed things up. But in the other direction, passengers also probably increased and so there’s a net-zero effect.”

Harris is among the thousands of Canadians to feel the frustration personally. He was slated to fly with his partner and three-year-old child to Toronto from Fredericton on June 9 for a four-day getaway. Air Canada cancelled the trip 21 hours before departure. The rebooked flight, which had a four-hour layover in Montreal, was also cancelled.

“We just went for a drive to P.E.I. instead,” he said.

“I said screw it, if I don’t get a vacation, I’m building a (data) dashboard.”

Philippe Rainville, CEO of Montreal’s airport authority, said in an interview global flight disruptions have knocked domestic schedules off course.

“It’s a consequence of the delay in international flights,” he said. “To delay a domestic flight is a lot easier because flying to major hubs in Europe, the slots are very tight. Domestically, we’ve got a lot more leeway.”

Luggage is an especially sticky problem, with a shortage of baggage handlers to shuttle suitcases from late arrivals to connecting planes amid last-minute gate changes.

“It creates a bottleneck and congestion and to some extent it’s a bit of a nightmare,” Rainville said.

In Montreal, the hiring spree by the federal airport security and customs agencies has “significantly improved” lineup times, he said. “It’s not perfect, but it is much better.”

While passenger volumes remain below 2019 levels, at peak times they’re on par. “We don’t have the personnel obviously for this. And we have all-new personnel as well that have just been freshly trained, and they’ve got to ramp up the learning curve, and that’s difficult,” he said, adding that staff retention is another hurdle.

“There’s not enough of them. And if you get sick, then they get sick too,” said Helane Becker, an aviation analyst for financial-services firm Cowen.

Kinks in one part of the air travel pipeline can snarl others, with overflowing customs areas stopping flight crews from disembarking, for example, or a lack of airline customer service agents exacerbating delays.

Flights held on the tarmac can leave crew out of “duty time” — the regulatory and contractual limits on hours worked — prompting personnel gaps. Agents tied up boarding passengers for a delayed flight can’t cover check-in counters, leading to delays in a different part of the airport. Similar snags confront baggage handlers.

Passengers say they receive last-minute emails informing them of repeated delays, aircraft changes or rebookings scheduled days after the original departure time. Reasons cited run the gamut from absent pilots to unplanned mechanical maintenance.

Air Canada has said it continues to hire, with 32,000 employees now on its payroll — nearing 2019 staffing levels — and its schedule operating at just 80 per cent of 2019 volumes, said spokesperson Peter Fitzpatrick.