Europeans have become used to cheap flights, sometimes paying no more than the price of a good meal for a ticket between London and Barcelona.
But last week's terrorist alert has cast a shadow over the era of budget flying, with fears that no-frills airlines won't be able to avoid passing on to their customers the costs of tougher long-term security measures.
"The situation as it is at the moment is unsustainable," David Bryon, an industry consultant and former managing director of low-cost airline bmibaby, said Monday.
Canceled and delayed flights since Thursday, when authorities revealed a plot to attack several trans-Atlantic flights, have already cost all carriers millions of pounds (dollars; euros) per day. Budget airlines could be even more susceptible to future costs.
That is because the no-frills carriers are particularly vulnerable to increases in "turnaround times" - the interval between when a plane's wheels hit the tarmac and when it takes off again with a new set of passengers.
Speedy turnaround times mean more flights and reflect the budget airlines' decision not to offer full onboard meals and to discourage passengers from checking bags - costly services that eat up time and staff on the ground. Fast groundwork is a primary way that the no-frills carriers keep down costs - and fares.
Ryanair Holdings PLC prides itself on a turnaround time of 25 minutes, while its major competitor easyJet PLC aims for just five minutes more. But with passengers stuck in lengthy queues at airports around the country because of strict security checks, those numbers are currently far out of reach.
"The problem is that the budget airlines work to tight schedules," said Bryon. "If you can't physically do that because of passenger checks, you can't meet your turnaround timetable, you have to consider changing your schedule and costs rise."
The government slightly eased strict security measures that had banned all carry-on baggage as the threat level was lowered Monday. The Transport Department said passengers would be allowed to carry a single, briefcase-sized bag aboard planes, and that books, laptop computers and digital music players would be permitted again.
But BAA PLC, the operator of Heathrow and other major London airports that has struggled to deal with the chaos, said it would not adopt the relaxed regime until Tuesday. It also ordered airlines to cut Monday's services by 20 percent or face the loss of all their flight slots, drawing complaints from airlines.
Bmibaby Chief Executive Nigel Turner said the airline was following BAA's directive but he hoped the situation would have returned to "pretty much as normal" by the end of the day.
EasyJet, which has canceled more than 500 flights since Thursday, continued to ask its passengers Monday to still pack everything into one piece of luggage for the hold in an attempt to minimize the volume of bags it has to deal with.
Ryanair, which has grounded a fifth of all scheduled departures since Thursday, was harshly critical of both the BAA and the government.
"The U.K. government, by insisting on these heavy handed security measures, is allowing the extremists to achieve many of their objectives," Chief Executive Michael O'Leary said.
Ryanair is particularly sensitive to restrictions on hand luggage after it this year began charging customers for each bag they checked as part of a plan to get passengers to take only what they could carry.
The airline temporarily waived its euro2.50 (US$3.20) fee for each carry-on bag that unexpectedly had to be checked, but said Monday that it had no plans to ditch the policy.
David Learmount of Flight International magazine said that stance was unsustainable in the long term as some form of more intense security checks were likely to remain in force.
Ryanair said the recent delays and cancelations were unlikely to affect its forecast for the number of passengers it expects to carry over the financial year because it bases the outlook on the number of tickets booked, rather than the actual number of passengers carried.
There are fears that no-frills airlines won't be able to avoid passing on to their customers the costs of tougher long-term security measures.
As the immediate security threat at British airports wanes, airlines are beginning to count the multimillion dollar cost of the terrorist alert - and consider who should pay.
Ryanair has a network of more than 360 routes serving 23 countries across Europe.
Budget airline Ryanair threatened to take legal action unless the British government meets three demands within the next seven days.