A reform of compensation rules is being urged by airlines after the disclosure that a single wrongly input flight plan to UK air traffic control disrupted thousands of flights.
An investigation is ongoing, with the Civil Aviation Authority due to deliver a first report to transport secretary Mark Harper on Monday.
Iata director general Willie Walsh told the BBC the cost to airlines could top £100 million.
Nats, which controls UK airspace, said “some of the flight data” received had caused the system failure on bank holiday Monday, leading to more than 1,600 flights being cancelled and many more delayed.
Walsh insisted that if Nats is fined, the costs should not be passed onto airlines.
He said that the UK should “look at the way passenger compensation is dealt with to ensure that the people who are responsible for the delays and cancellations ultimately bear the costs”.
Addressing the Nats meltdown, Walsh said in a statement that the organisation had “crucial questions to answer” about its responsibility for the “fiasco”.
Walsh added: “The failure of this essential service is unacceptable and brings into question the oversight of the CAA who are required to review the Nats resilience plan under the terms of its licence.
“This incident is yet another example of why the passenger rights system isn’t fit for purpose.
“Airlines will bear significant sums in care and assistance charges, on top of the costs of disruption to crew and aircraft schedules. But it will cost Nats nothing.
“The UK’s policy makers should take note. The passenger rights system needs to be rebalanced to be fair for all with effective incentives. Until that happens, I fear we will see a continuing failure to improve the reliability, cost efficiency, and environmental performance of air traffic control.
“The current system does not protect passengers. It hurts them.”
Advantage Travel Partnership chief executive Julia Lo Bue-Said, responding on X to the explanation by Nats chief executive Martin Rolfe, said: “Now we know what caused chaos of monumental proportions, people displaces around the world, airlines, travel agents et al working around the clock to bring people home, out of pocket, stressed and tired, but who picks up the tab Martin?”
EasyJet laid on additional repatriation flights from Spain and Portugal as stranded passengers reported having to sleep on floors, amid criticism of airlines for failing to look after customers.
CAA joint interim chief executive Rob Bishton said on Wednesday: “The scale of the disruption has meant passengers have faced longer delays and in some cases are waiting several days for alternative flights, but airlines are working around the clock, putting on extra capacity to resolve the issue.
“Clear and accurate communication is important during times of disruption, and we are working closely with airlines to rectify any instances of wrong information being provided to passengers.”
EasyJet said that flights were operating normally on Wednesday, adding: “We are continuing to work hard to support customers disrupted by these events and are now providing extra capacity on flights across our network to help bring affected customers back home. Extra seats will now be available for impacted customers on many flights back to the UK.
“To ensure that we can support as many affected customers as possible, seats on these flights will be offered on a first come, first served basis.”
In an update at 3.30am today (Thursday), Jet2, which had cancelled some outbound flights on Monday and Tuesday, said: “We are reviewing today’s programme as the situation evolves, and we will update customers in due course.
“Customers due to travel tomorrow should travel to the airport as normal unless we advise otherwise, and continue to monitor flight information on our website.”
Tui said: “We would like to reassure customers currently on holiday and due to fly home that their flight will operate but may be subject to delay.”
For people due to fly on holiday, the operator added: “We are expecting Tui Airways flights to be operating as scheduled and will be in touch with customers directly should travel plans change. Customers should travel to the airport as usual, unless contacted directly by Tui and told otherwise.
“For customers travelling on a Tui package holiday but with an alternative airline, for example EasyJet or British Airways, and have been advised their flight has been cancelled, our customer services team will be in contact directly to discuss options.”