It looks to be pretty limited service though - for example, AB does Sundays only from 4/27 - 10/18, with some Tue flights in late July-August from TXL and AB/Niki does routes from VIE, DUS, MUC etc if I'm reading their online schedules correctly (e.g., some may be direct and not nonstop flights). Be a bit flexible in your days of the week and you'll likely find something so long as it's during the April - October timeframe.