BRUSSELS (Reuters) - Ryanair will have to revise down its passenger traffic estimates for next year because of expected aircraft delivery delays from Boeing ( BA ), the budget airline's group CEO Michael O'Leary told Reuters on Wednesday.

"We were supposed to get 20 deliveries before the end of December. They'll probably come now in January and February, and that's fine. We'll have them in time for next summer. The big issue for Ryanair is we're due 30 aircraft in March, April, May and June of next year, and how many of those will we get?" O'Leary said in an interview.

"We want to avoid next year what we had this year. We had geared up, we crewed up the 50 aircraft, and then we only got 30 .... we were overcrowded, over-staffed. We took a significant cost penalty this year," he added.