British Airways-owner IAG plunged to a record $9 billion loss last year as travel paralysis saw it burn through cash.
It warned on Friday (February 26) it could not say when normal flying conditions would return.
Tighter restrictions brought in by countries over the last two months have threatened to ruin Europe's critical summer season.
That's left some airlines in need of another round of funding support.
IAG's CEO said it's "calling for international common testing standards and the introduction of digital health passes to reopen our skies safely".
For now, the firm is focussing on cutting costs to reduce cash burn.
UK-focused airlines were buoyed earlier this week when Britain laid out plans for travel markets to possibly reopen from mid-May.
That prompted a flood of bookings, but it's unclear whether that might include IAG's long-haul routes.
Shares in the group were up around 4% in morning trading.
They have jumped 13% over the last five days, after Britain's announcement.
But over the last 12 months they have halved in value.
The group, which also owns Aer Lingus, Iberia and Vueling, has been trying to boost its finances as the crisis drags on.
BA recently secured an extra 3.4 billion dollars through a UK government-backed loan and from deferring pension contributions.
And in October, IAG secured shareholder backing for a 3.3 billion dollar capital hike, adding to savings made from around 13,000 planned job cuts.