(Updates with start of case; quotes from Ryanair lawyer)
DUBLIN, Dec 3 (Reuters) - Ryanair launched a bid in Ireland's High Court on Tuesday to prevent operations chief Peter Bellew from joining arch-rival easyJet until 2021, saying he possessed information of immense competitive value and that he had signed a non-compete clause.
Europe's biggest budget airline said in July that the former Malaysia Airlines boss, who denies that he is bound by such a clause, would step down at the end of the year.
But after easyJet announced Bellew's appointment as its new chief operations officer a week later, Ryanair filed legal proceedings to try to block him.
On the opening day of the case, a lawyer representing Ryanair listed information he said the airline could not allow to be passed to its rival, including details of delays to the delivery of Boeing's grounded 737 MAX aircraft as well the terms of deals Ryanair has signed with airport baggage handlers.
Delays to the 737 MAX have slowed down Ryanair's growth plans and it said last month they risked effectively halting the Irish airline's expansion next summer.
"Mr Bellew has all of this information ... in his head, and it would be of immense benefit to a rival," senior counsel for Ryanair Martin Hayden told the court.
A delay of 12 months would mean information would be far less relevant, he added.
Hayden told the court that the initial contract Bellew signed in October 2017 did not include a non-compete clause, but said a bonus scheme accepted by Bellew at the time barred him from joining a competitor for 12 months after leaving Ryanair.
Bellew received a bonus payment of 1.13 million euros ($1.25 million) in June this year, the court heard.
Ryanair boss Michael O'Leary, who sat across the courtroom from Bellew, said in September the timing of Bellew's switch was particularly sensitive because of the problems with the 737 MAX and that he should only start the new job in January 2021.
Bellew left his role as CEO of Malaysia Airlines two years ago to return to Ryanair, where he had been director of flight operations before leaving for Kuala Lumpur in 2014.
Tasked with tackling a pilot revolt that resulted in Ryanair's first ever strikes, Bellew was part of an effort to patch up relations with staff and agree deals on pay and conditions with trade unions that have quelled the unrest.
But he was told by O'Leary in March that he would need to show "significantly improved performance" and would not be offered a fresh share option, Hayden told the court.
Hayden said Bellew only told O'Leary of his plans to move to easyJet a day before the British company announced the plan. Correspondence between Bellew and O'Leary "gets quite fulsome" after this, he told the court.
An Irish national, Bellew described his return to Ryanair in 2017 as "a form of national service" to help what he described as Ireland's greatest company. Some observers had seen Bellew as a possible future Ryanair chief executive.
An easyJet spokeswoman declined to comment on the case. Bellew has not commented on the case since Ryanair initiated proceedings.
($1 = 0.9073 euros) (Reporting by Padraic Halpin; Editing by Mark Potter)