A gas turbine engine comprising: a high spool along an engine axis, said high spool operable to communicate a core airflow through a core flow path; a fan section operable to communicate a fan airflow into a secondary flow path and said core flow path; a low spool along said engine axis to drive said fan section; a starter/generator connected to said low spool; a flow control mechanism operable to direct at least a portion of said fan airflow from said secondary flow path into said core flow path; and a module configured to execute an engine start mode algorithm; characterized in that: said flow control mechanism is a two-piece fan duct blocker vane ring comprising a static ring and a movable ring which is selectively rotatable relative to the static ring; the gas turbine engine further characterised in that the module is configured such that in a flight mode the static and movable rings (64, 66) are in a first relative rotational position being in line to form an aerodynamic shape to communicate fan airflow into the secondary flow path and the starter/generator operates in a generate mode, and in a start mode the static and moveable rings (64, 66) are in a second relative rotational position being staggered to form a wall to redirect all or a percentage of the fan airflow into the core flow path to start the engine and the starter/generator operates in a starter mode. a high spool along an engine axis, said high spool operable to communicate a core airflow through a core flow path; a fan section operable to communicate a fan airflow into a secondary flow path and said core flow path; a low spool along said engine axis to drive said fan section; a starter/generator connected to said low spool; a flow control mechanism operable to direct at least a portion of said fan airflow from said secondary flow path into said core flow path; and a module configured to execute an engine start mode algorithm; characterized in that: said flow control mechanism is a two-piece fan duct blocker vane ring comprising a static ring and a movable ring which is selectively rotatable relative to the static ring; the gas turbine engine further characterised in that the module is configured such that in a flight mode the static and movable rings (64, 66) are in a first relative rotational position being in line to form an aerodynamic shape to communicate fan airflow into the secondary flow path and the starter/generator operates in a generate mode, and in a start mode the static and moveable rings (64, 66) are in a second relative rotational position being staggered to form a wall to redirect all or a percentage of the fan airflow into the core flow path to start the engine and the starter/generator operates in a starter mode. said flow control mechanism is a two-piece fan duct blocker vane ring comprising a static ring and a movable ring which is selectively rotatable relative to the static ring; the gas turbine engine further characterised in that the module is configured such that in a flight mode the static and movable rings (64, 66) are in a first relative rotational position being in line to form an aerodynamic shape to communicate fan airflow into the secondary flow path and the starter/generator operates in a generate mode, and in a start mode the static and moveable rings (64, 66) are in a second relative rotational position being staggered to form a wall to redirect all or a percentage of the fan airflow into the core flow path to start the engine and the starter/generator operates in a starter mode.