Hi AJ,
Yes charter airlines usually contract for the summer period only with new people. i.e. start around April, May, June and contract will finish 31st October. This is the end of the summer season. You will be asked back next summer depending on your performance and operational requirements.
You could be lucky and get a permanant contract at the end of this period. But not generally so with bigger airlines, such as Mon, By etc. for example, I was three years temporary with By, but have known people to be 5 years temp.
If you are desperate for permanent contract need to go for scheduled or smaller airlines, where promotion is quicker.
Good luck....