Officer Kite is correct, only 8 will be selected to start in June. It doesn't sound like a promising figure, but if last year's assessment candidate numbers are anything to go by, then only 30-40 will be invited to attend the assessments in March.
Also, Although the website does state clearly that there will only be one assessment this time around, this was also the case last September, and the top candidates were given a personality questionnaire to complete. I'm guessing the top 6 performing candidates from this group were then offered positions with Flybe. Whether fte and Flybe choose to adopt this procedure this time around or not I don't know, but I'd be surprised if they just picked the 8 best candidates from one assessment day.