A gas turbine engine includes a fan duct including a fan duct inner structure that surrounds a core engine, a fan case that surrounds a fan, a core engine frame, and at least one mechanism configured to secure a portion of the fan duct inner structure to a portion of the core engine frame. The at least one mechanism includes a castellated arcuate portion mounted to one of the fan duct inner structure and the core engine frame and an inwardly projecting retaining feature mounted to the other of the fan duct inner structure and the core engine frame. The castellated arcuate portion is rotatable about an engine central longitudinal axis to position a feature of the castellated arcuate portion proximate to a portion of the inwardly projecting retaining feature to latch the fan duct inner structure.