Dozens of routes serving the UK's regions could be left without services after the collapse of Flybe.
Scotland's Loganair has committed to maintaining 16 routes, but many smaller airports still face gaping holes in their schedules.
The carrier, Europe's largest regional operator, went into administration early on Thursday, after a bid for fresh financial support failed.
Flybe boss Mark Anderson said he was "very sorry" for the firm's collapse.
He told staff one of the firm's shareholders had pulled out at the start of this week, and he had spoken "frantically to the government" asking for rescue aid, but that they had run out of time on Wednesday night.
What is happening to Flybe's flights?
All of Flybe's flights have been cancelled and customers with bookings should not travel to the airport unless they have arranged an alternative flight.
Flybe operated 210 flights, serving the UK's regional airports and dominating routes out of Southampton, Exeter and Belfast. But it also linked regional airports with more than a dozen other European destinations.
In response to the collapse, the UK government said it would work with other airlines to replace services.
Aviation minister Kelly Tolhurst said the government also "stands ready" to support regional airports affected by the collapse.
She said: "We recognise the impact that this will have on UK airports particularly those which have large-scale Flybe operations."
Will the regions lose those services?
Although Flybe is small compared to the likes of British Airways, Ryanair or EasyJet, the loss of the operator has been described as "disastrous" for UK regions.
Air transport expert John Strickland said Flybe is "small in the scale of the UK market as a whole, but if you're flying out of Exeter, Newquay or specifically Southampton it really is one of the only airline choices... so a number of regional groups will risk not being served".
However rival airlines are interested in operating at least some of the routes.
Loganair has opened a special recruitment line for former Flybe employees as it works on plans to salvage services on 16 of Flybe's 120 routes. They include flights from existing bases for Loganair, including Aberdeen, Edinburgh, Glasgow, Inverness and Newcastle.
Belfast City airport said it was in talks with multiple airlines to fill the routes left empty; 77% of its routes were operated by Flybe.
Brian Ambrose, chief executive of Belfast City Airport, said he was "pleased" that Loganair will backfill routes between Belfast and Aberdeen and Inverness, less than 24 hours after Flybe entered administration.
Tim Jeans, chairman of Cornwall Airport, said that he "very much hoped" that other airlines would take up vacant routes. He said discussions with other airlines would "begin in earnest" soon and he hoped to reinstate services "on those routes hopefully within weeks rather than months".
What are your rights as a passenger?
Passengers arrived at several airports on Wednesday morning to find their flights had been cancelled.
David Manners was due to fly to Paris as part of a surprise Christmas present for his wife. He said they were "absolutely gutted".
Flybe customers who bought tickets directly from the company will not be protected by Atol, the travel industry insurance fund.
However, if you bought through a travel agent or other third party you might be covered.
Some people might be able to get their money back if they paid by credit card or with some debit cards.
What does it mean for staff?
Thousands of jobs are at risk following the regional airline's collapse.
Katherine Densham, a Flybe cabin crew member, had been due to fly to London City Airport from Exeter on Thursday. She has worked for the airline for 13 years after joining the firm straight from college.
She told the BBC that staff were feeling "really sad" and that she was not sure what to do next.
Balpa, the pilots' union, said that pilots, cabin crew and ground staff "have done their jobs brilliantly" throughout its struggle.
Companies including Loganair and South Western Railway have already been calling out for job applications from Flybe staff on social media.
What went wrong at the airline?
Flybe ran into difficulties last year and was bought by a consortium that includes Virgin Atlantic.
But its troubles persisted, and it narrowly avoided going bust in January this year. The new owners said they would pump £30m into the business to keep it afloat, but appealed to the government for additional support.
Virgin Atlantic pulled the plug and was not willing to invest more money, a source told the BBC.
Virgin Atlantic said it was "deeply disappointed" that Flybe had gone bust, adding that the consortium had invested more than £135m in keeping the airline flying for an extra year.
Flybe, which served destinations from the Channel Islands to Aberdeen, had also been hoping for a £100m lifeline from the government and changes to Air Passenger Duty taxes.
The news that it may benefit from government help sparked a backlash from its rivals. British Airways-owner IAG filed a complaint to the EU arguing Flybe's rescue breached state aid rules.
John Strickland added that the regional market was extremely challenging for any airline, but that Flybe had made matters worse some years ago through over-ambitious expansion.
"It's really too big for what it's trying to do," he said.
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