The carrier said it is taking action to reduce its services after slashing its expected growth rate for the summer 2020 from 7% to 3%.
The airline is in talks with airports over which loss-making bases will be affected and is set to consult with staff and unions over the planned “short-term” cuts and closures for winter 2019 through to summer 2020.
Ryanair is waiting for delivery of Boeing’s MAX 200s – a version of the MAX aircraft – which will need to be certified separately by aviation authorities.
The firm said it “remained committed” to the B737 MAX aircraft and expects it will return to flying service before the end of the year, but admitted the exact date is “uncertain”.
The MAX 200 jets it has ordered are set to be approved within two months of the MAX’s return to service.
The delays mean Ryanair plans to cut its aircraft to 30 for next summer, down from 58.
Full-year passenger traffic growth is now forecast at around 157 million for the year to March 2021, down from 162 million previously expected.
Ryanair boss Michael O’Leary said: “Ryanair remains committed to the B737 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.”
He added: “This shortfall in aircraft deliveries will necessitate some base cuts and closures for summer 2020, but also for the winter 2019 schedule.”
The group said it hopes to “restore our growth to normal levels in summer 2021”.