British Airways owner IAG has called for digital health passes "to reopen our skies safely" as it posted a record loss for 2020 due to Covid disruption.
IAG posted an operating loss of €7.4bn (£6.5bn) for last year after the pandemic grounded many of its flights.
UK-focused airlines got a boost this week from government plans for travel markets to possibly reopen from mid-May, prompting a flood of bookings.
But uncertainty remains about what routes will be available.
The airline group - which also owns Iberia, Aer Lingus and Vueling - called for "a clear roadmap for unwinding current restrictions when the time is right."
"We're calling for international common testing standards and the introduction of digital health passes to reopen our skies safely," said IAG's boss Luis Gallego.
IAG said that the ongoing uncertainty and duration of the pandemic meant that it could not provide a forecast for future profits.
Laura Hoy, equity analyst at Hargreaves Lansdown, said: "There's no getting around just how ugly IAG's final results are.
"With the coronavirus crisis clearing the skies for over a year, it's not unexpected to see IAG operating as just a shell of its former self.
"Management has responded in the only possible way - by securing new funding and slashing costs - but ultimately the group is at the mercy of the government's travel restrictions."
The government is in the process of talking to to G7 and other countries to try to build a consensus on how to allow more foreign travel.
Greek tourism minister Haris Theoharis told the BBC last week that early technical discussions were underway with UK officials about how a potential passport scheme might work.
The International Air Transport Association (IATA) also said this week that it expects its digital Covid Travel Pass will be ready soon.
The pass is an app that verifies a passenger has had the Covid-19 tests or vaccines required to enter a country. It also verifies they were administered by an approved authority.
Transport Secretary Grant Shapps said a review of how to return to international travel while managing risk from imported cases and virus variants would report on 12 April.
IAG said that revenues last year sank by 69% from €25.5bn to €7.8bn amid the coronavirus-related restrictions on travel.
During 2020 it operated at a capacity of just 33.5% of the levels seen in 2019, and for January to March this year it expects capacity will drop to just 20% of pre-pandemic levels.
The airline group has been trying to boost its finances as it burns through cash in the pandemic.
Most recently, BA secured an extra £2.45bn through a UK government-backed loan and from deferring pension contributions.
Last October, IAG got shareholder backing for a €2.74bn rights issue, adding to savings made from 12,000 planned job cuts.
Despite the hefty losses, IAG has stuck to its plan to buy Spain's Air Europa, announcing in January the price tag had halved to €500m, with payment deferred for six years.