A freeze on entitlements to take-off and landing slots at once-busy airports has eased some of the pressure on incumbent airlines.

But budget carriers are likely to pull off a nimbler restart, observers say, thanks to more variable costs and robust balance sheets to underpin risk-taking and discounting.

"It's not only much easier to ground all of your fleet, it's easier to put your aircraft back in the sky," said Geoffrey Weston, a Bain & Co. partner who heads the management consultancy's global transport business.

"You're winning on the way down and you're winning on the way up."