The chief executive of Ryanair says the grounding of the Boeing 737 MAX fleet is costing the airline at least €100m (£84m) a year.
Michael O’Leary was speaking as the no-frills carrier cuts services and continues to downgrade its growth plans in the wake of delays to the delivery of its first of 135 MAX planes.
Ryanair sees the aircraft as crucial to its expansion and cutting costs, particularly fuel bills, as part of its fleet modernisation programme.
But all versions of the 737 MAX were grounded worldwide in March – days after an Ethiopian Airlines jet came down outside Addis Ababa and five months after a Lion Air flight suffered a similar fate in the Java Sea.
A total of 346 people died.
Boeing has been working with US regulators to ensure the planes are safe – with modifications focusing on an anti-stall device called the Maneuvering Characteristics Augmentation System (MCAS) in the hope of returning the MAX to service.
The Federal Aviation Administration (FAA) is not now expected to grant clearance for US flights until January at the earliest, according to US officials.
European regulators would need to give their own approval at a later date, with pilots also having to undergo re-training before 737 MAX commercial operations could resume within European airspace.
Ryanair has said it will be claiming compensation from Boeing.
The airline had said, in an investor update last week, that the latest cut to its passenger traffic forecast was based on the expectation of 10 new MAX aircraft being delivered by June.
But, in an interview with the Reuters news agency, Mr O’Leary admitted the company may not receive any of the aircraft it is expecting by next summer.
He claimed testing delays at the European Union Aviation Safety Agency would mean the planes remaining grounded in Europe until May at the latest.
“We’re still looking to meet with Boeing in mid-early January.
“We expect the Max to be back flying in early January, particularly in North America. We think it could be a bit slower in Europe because the EASA seems to be dragging their heels a little bit,” he said.
He was speaking as Congressional hearings into the fatal MAX crashes continue in Washington.
The US House Transportation and Infrastructure Committee is due to hear on Wednesday from a former senior operations manager who had warned, in a company email ahead of his retirement last year, that he was “hesitant about putting my family on a Boeing airplane”.