Ryanair is expecting to welcome five million fewer passengers next summer as the grounding of the Boeing 737 Max impacts capacity growth.
The Irish airline has a total of 135 of the controversial models on order, the first five of which are due for delivery this autumn.
However, the aircraft has not flown since fatal crashes in Ethiopia and Indonesia killed 346 people.
Boeing is currently seeking to improve software on the plane to have it recertified by the FAA and other global authorities.
After weeks of uncertainty, it now appears this will take well into the autumn.
As a result, Ryanair now expects to receive 30 new Boeing 737 Max planes from the manufacturer next year, down from the original 58 planned.
The carrier will now seek to grow capacity by three, rather than seven, per cent next summer.
Ryanair hopes to welcome 157 million passengers in the year to March 2021, down from an originally anticipated 162 million.
Ryanair chief executive, Michael O’Leary, said: “Ryanair remains committed to the Boeing 737 Max aircraft, and now expects that it will return to flying service before the end of 2019, however the exact date of this return remains uncertain.
“Boeing is hoping that a certification package will be submitted to regulators by September with a return to service shortly thereafter.
“We believe it would be prudent to plan for that date to slip by some months, possibly as late as December.
“As Ryanair have ordered the Boeing Max 200s, which are a variant of the Max aircraft, these need to be separately certified by the FAA and EASA.
“Ryanair expects that the Max 200 will be approved for flight services within two months of the Max return to service.”
A number of bases will also be closed to accommodate the falls.
“We are starting a series of discussions with our airports to determine which of Ryanair’s underperforming or loss-making bases should suffer these short-term cuts and/or closures from November,” O’Leary added.
“We will also be consulting with our people and our unions in planning and implementing these base cuts and closures, which are directly caused by the Boeing 737 Max delivery delays to the Boeing 737 Max program.”