China and Indonesia grounded their fleets of Boeing's 737 MAX 8 aircraft after the fatal crash. Ryanair has ordered 135 of the 737 MAX 200 planes, a modified version of the MAX 8, and has options on 75 more.

"We wouldn't take any action at the moment," O'Leary told the Irish Independent newspaper in an interview. "We need to wait and see what the outcome of the investigation will be."

A Ryanair spokesman did not immediately respond to a request for comment.

Ryanair is due to take delivery of the first 737 MAX in April, two in May and two in June. It will then take 50 more deliveries before the 2020 summer season.

"They've recovered the black box this morning I understand, so we'll wait and see what Boeing and the safety agencies [say]," O'Leary was quoted as saying.

O'Leary said he was "not particularly" concerned and that he expected the investigation into the crash to have been completed before the first delivery is made.

(Reporting by Conor Humphries, Editing by Rosalba O'Brien)