The global aviation industry is preparing to fly again. Heathrow Airport, one of the world’s biggest gateways, illustrates how hard that will be until governments decide how to allow overseas travel.Big chunks of the U.S. and Europe are following Asia in reopening their economies as Covid-19 infection rates start to ebb. But despite signs of rebounding demand in sectors like retail, fliers so far aren’t returning to the skies in large numbers. United Airlines Holding Inc., for instance, is expecting June revenue to be about 90% lower than last year.

Airlines and airports are partly blaming a standstill in international travel on governments, for not lifting travel bans, quarantines and other restrictions more quickly. Australia’s Qantas Airways Ltd. said Thursday that it was canceling most international flights through October. The move came after the Australian government indicated it would keep its borders shut to most international travelers until next year to help curtail the spread of the coronavirus.

“In five or 10 years’ time the market will be bigger,” Heathrow Chief Executive John Holland-Kaye said. “But how quickly really depends on how quickly we can get countries to reopen their borders.”

Heathrow is Europe’s busiest airport and No. 2 in the world in terms of international traffic, behind Dubai. It is now at the center of a divide between industry executives and government and public-health officials over how and how quickly to resume significant international air travel. The U.K., for instance, has said travelers coming into the country will be subject to a strict two-week quarantine once they land. Airlines and Heathrow have fought back, but so far the government isn’t softening its stance.

Air travel is full of opportunities for coronavirus transmission. Touchless check-in, plexiglass shields, temperature checks, back-to-front boarding and planes with empty middle seats are all now part of the flying experience, and the future may bring even more changes. Illustration: Alex Kuzoian

This month will be a test case. On Monday, the European Union cleared its citizens to travel across the bloc, and in some cases beyond, many with minimal conditions. U.S. carriers—though cautious on how quickly fliers will return—have nevertheless promised to increase domestic capacity this summer. American Airlines Group Inc. expects domestic flights in July to be about 55% of its capacity compared with the same month last year.

American’s international capacity, though, is expected to remain at around 20%, reflecting a patchwork of global flying bans, differing requirements around the world for quarantines for passengers, and fast-changing guidance from countries over who can fly where.