Ryanair outlined the scale of disruption its passengers suffered due to the NATS air traffic control meltdown.
It was forced to cancel over 350 flights and overall, it impacted 63,000 passengers.
NATS had to severely limit departures last week and use manual flight management after a system failure.
It happened on one of the busiest days of the year for summer travel.
In total, there were nearly 1,600 flights in and out of the UK grounded over three days.
Still, Ryanair enjoyed its busiest month of the year, carrying 18.9 million passengers, up 11% on a year ago.
It handled 18.7 million in July.
Ryanair railed at NATS, saying the system failure ‘has still not been explained.’
The fallout has sparked calls to amend rules on who is liable to compensate for flight disruptions and refunding passenger expenses.
The International Air Transport Association has called for a review of the system.
Willie Walsh, DG of IATA, said: “It’s very unfair because the air traffic control system, doesn’t pay a single penny.”
IATA predicts the disruption could cost airlines £100 million.
