Flybe has been forced to cancel flights and cut frequencies this summer due to late aircraft deliveries.
The schedule is being reduced between July 28 and October 29.
Routes from Belfast City to Aberdeen, Inverness and Newcastle and Birmingham-Aberdeen have been suspended for the summer.
Flights are also being trimmed from Belfast City to Birmingham, Edinburgh, Glasgow, Manchester and Southampton as well as Birmingham to Edinburgh and Glasgow.
Chief executive Dave Pfliger said: “This is not a decision we’ve have taken lightly, and as you would expect we are in daily conversations with all involved to see if anything might change that would allow us to resume our original plans at an earlier date.”
He told customers: “It is essential that we take action now to ensure you have enough time to change your travel plans, be re-accommodated on a different flight or, if that is not desired, obtain a full refund.”
Pfliger explained: “We were planning to increase flights to existing cities and new destinations such as Aberdeen, Inverness, Newcastle, and Southampton.
“However, the two aircraft leasing companies who were contracted to provide our additional airplanes have now told us that they will be unable to fulfil their commitments until after the summer.
“We were able to find and rent aircraft from two separate airlines in Greece and Spain, but those planes are not enough, and the lack of additional aircraft needed for new flying means we need to adjust our future flight schedule.”
He added: “The new schedule will be fully supported by the aircraft we do have available, and we will still introduce more flights later this year – after we receive our delayed aircraft.”