LONDON (Reuters) -An air traffic meltdown in Britain was caused by a "one in 15 million" event, the boss of traffic control provider NATS said, as initial findings showed how a single flight plan with two identically labelled markers caused the chaos.
Thousands of passengers were stranded abroad for days after 1,500 flights were cancelled on Aug. 28, during one of the busiest travel periods of the summer.
"This was a one in 15 million chance. We've processed 15 million flight plans with this system up until this point and never seen this before," NATS CEO Martin Rolfe told the BBC, as airlines stepped up calls for compensation for the breakdown.
A preliminary NATS report said the flight plan met European standards but included two identically named but separate waypoints or navigational markers outside UK airspace, which forced the system - and its back-up - to enter a "fail-safe" mode.
The system had faced the dilemma of neither being able to reject the flight plan without knowing what impact that might have, nor approve it and hence risk providing wrong safety-critical information.
"It therefore stopped operating, avoiding any opportunity for incorrect data being passed to a controller," the report said.
NATS management had "some serious explaining to do," Willie Walsh, director general of airline industry body IATA, said in a blog post. He called for compensation to airlines and repairs to the control system funded by NATS budgets.
Michael O'Leary, CEO of budget giant Ryanair, said in a video posted on X, formerly Twitter, that the report was "full of rubbish" and that "heads should roll" at NATS.
Rolfe said a few days ago that the problem would not be repeated.
Britain's civil aviation regulator, the CAA, will review circumstances surrounding the failure and assess if further action is necessary, joint interim CEO Rob Bishton said.
IATA has said the episode could cost airlines up to 100 million pounds ($126 million) as passengers whose flights were cancelled will be able to claim back expenses for the hotels they stayed in or the new tickets they bought.
Ryanair rival easyJet said the NATS report left some questions unanswered and called for a wide-ranging examination of its resources and IT systems "to ensure it is fit for purpose today and in the future."
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(Reporting by Muvija M, Farouq Suleiman, Sarah Young, Tim Hepher; editing by William James and John Stonestreet)