Ryanair announced plans to cancel some flights and hubs starting in November 2019, blaming delivery delays of Boeing 737 MAX planes.
The CEO of Europe's second-biggest airline said the airline was talking to airports about which locations could suffer cuts.
"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 2019," Ryanair CEO Michael O'Leary said.
The delays come after Boeing's 737 MAX planes were grounded following the Ethiopian Airlines crash that killed 157 people in March. The same Boeing aircraft crashed in October 2018, killing 189 people after taking off from Indonesia.
Initial information from the crashes suggested they were linked to the same automatic software problem, and as a result, the airlines around the world grounded the plane.
O'Leary said he expected the 737 MAX planes to return before the end of 2019, but did not have an exact date.
The Irish airline was expecting 58 new 737 MAX planes before next summer but now expects only 30 new planes.
"This number could rise, or fall further, depending on when the Boeing 737 MAX actually returns to flight services," O'Leary said in a statement.
This would cut the airline's expected growth rate next summer from 7% to 3%, and result in five million fewer guests than expected through March 2021.
They are also expecting a variant of the 737 aircraft, which they are calling a MAX200 aircraft, in January and February 2020, but can only receive 6 to 8 new aircraft each month.
The company has ordered 135 737 MAX aircraft from Boeing.
A Boeing spokesperson told Euronews in a statement that the company regrets the impact the grounding is having on the airline.
"Boeing is working very closely with the FAA on the process they have laid out to certify the 737 MAX software update and return the MAX to service. We will submit the final software package to the FAA once we have satisfied all of their certification requirements," a Boeing spokesperson said in a statement.
Boeing said they would not speculate on the timing since it depends on regulatory authorities determining the process for "certifying the MAX software and training updates".
American Airlines said on Sunday that the airline would extend cancellations of 737 MAX routes through November 2, saying it amounted to a total of 115 flights cancelled per day.