I'm not surprised; Advances (the cheap, fixed-train-only tickets) have not yet been released for that route on that date. In fact, according to the section on TransPennine Express here, it is possible that they will not be released at all (it is not quite clear whether Advances for that date/route are "closed" for now, or "closed" full stop).I'm looking to buy tickets from Newcastle to Manchester airport on the 29th Dec returning on 1st Jan. Would it be best to wait till a later date to book? There doesn't seem to be any cheap seats at the minute