Following on the heels of the international success of Unknown, Dark Castle Entertainment has acquired the airplane thriller spec Non-Stop. Jeff Wadlow (Never Back Down and Cry Wolf) is attached to direct the pic which is co-written by first-timers John Richardson and Chris Roach. Per Heat Vision, Non-Stop is being developed as a gritty actioner that follows an air marshall who encounters some sort of unexpected turbulence while on a domestic flight. Joel Silver will co-produce the film alongside Andrew Rona and Alex Heineman. Silver and Wadlow previously worked together on the CBS pilots Hail Mary and The Odds.