David Kennedy was CEO until the early 1990s, from about 1974. Prior to him, there were quite a few long standing CEOs, such as Jeremiah Dempsey and Michael Dargan.
Since David Kennedy, there have been Garry Cullen, Peter Owen (who was a contract CEO anyway), Willie Walsh and Dermot Mannion. I am sure I am missing someone there, but I don't think that's too bad record.