The cuts will involve the scrapping of three of the routes, which were due to have been launched in August.
Flights from Aberdeen and Inverness to Belfast were due to have begun on August 26, and Aberdeen-Birmingham services on August 18.
Up to two flights a day on the other routes will be grounded between July 28 and October 29.
Flybe was not immediately able to say how many passengers would be affected by the cancellations.
Flights on the airline’s Birmingham, Manchester, Newcastle and Southampton to Belfast City routes will also be reduced, starting on July 28.
The announcements met with an angry reaction from some passengers.
Sarah Mckinley, from Birmingham, tweeted: “All flights to Aberdeen cancelled for the foreseeable future!
"Not looking good just as you get back up and running.”
A Flybe spokesperson said: “Due to a delay in our scheduled aircraft deliveries from our two aircraft leasing companies, we have had to make the difficult decision to reduce planned increases in our summer flying schedule during the period from July 28 to October 29, resulting in cancellations.
“Every attempt has been made to contact those affected, and we will do everything we can to re-accommodate our customers on the next available Flybe flight or, if this is not possible, provide a full refund.
“We understand the disappointment and frustrations these cancellations will cause and sincerely apologise to those customers who have been affected.”
In a letter to passengers, airline chief executive Dave Pflieger wrote: “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.
"We will still introduce more flights later this year – after we receive our delayed aircraft.
“This is not a decision that I 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.”
Flybe collapsed in 2020, but was relaunched in March under new owner Thyme Opco, which is linked to US hedge fund Cyrus Capital.
Its first flights were launched the following month.
Most of Flybe’s routes have brought it into competition with EasyJet or Loganair.
The original Flybe went into administration in March 2020, with the onset of the Covid pandemic seen as the final straw for the ailing airline, which had struggled with high operating costs.
The carrier, whose headquarters has been switched from Exeter to Birmingham, previously had the most routes within the UK.