But there's very little seasonal employment in the airline sector. They aren't going to spend 6-8 weeks training someone just to lay them off after a couple months.
One of the most notable carriers that did seasonal employment was USA3000. While it was not officially seasonal, if you were fairly junior you would regularly get furloughed for the summer season. They are in the slow process of going out of business, with a goal of being totally done by fall of 2012.