Ryanair  on Thursday promised its pilots significant improvements in pay and conditions, saying it would exceed rates paid by rivals and improve job security, according to a letter to pilots seen by Reuters.

The Irish airline, the largest in Europe by passenger numbers, has in recent weeks announced the cancellation of thousands of flights, saying it did not have enough standby pilots to ensure the smooth operation of its schedule.

Unions have said a significant number of pilots have left Ryanair in recent months to get more secure contracts, better pay and improved conditions at rival airlines.

Ryanair last week said reports it had a pilot shortage were false, saying less than 260 of its 4,200 pilots had left so far this year and that it was in the process of hiring 650 more.

On Thursday Chief Executive Michael O‘Leary sent a three-page letter to its pilotspromising “significant improvements to your rosters, your pay, your basing, your contracts and your career progression over the next 12 months.”

The letter, addressed to “all Ryanair pilots”, said Ryanair would “beat” the pay and job security offered by fellow Boeing 737 operators Jet2 and Norwegian Air Shuttle.

He repeated a promise to increase pilots’ pay by between 5,000 euros ($5,856) and 10,000 euros per year at four key bases and to negotiate with pilots at other bases about increases. He also pledged to offer a loyalty bonus of between 6,000 and 12,000 euros for pilots still employed at the airline in 12 months’ time.

But he added a new offer to match local employment conditions where they differ from the Irish contracts under which all Ryanair pilots work, another key demand of the pilots.

Changes to the roster systems would mean that “your days off will really mean days off,” he added.

The conditions mirror demands made in a letter by pilots at a number of Ryanair’s 86 bases last month. While Ryanair does not recognize trade unions, pilots have been using social media to organise in recent months.

The often outspoken O‘Leary, who last month said he “would challenge any pilot to explain how this is a difficult job,” praised his pilots in the letter, describing them as “the best in the business.”

He said the critical comments made at last month’s annual general meeting had been misreported and were specifically directed at pilots of competitor airlines and their unions.