Final answer:
Localizer full scale deflection is typically ±1 degree of angular deviation. Pilots may see an OFF flag or localizer failure flag when outside the acceptable localizer range during approach.
Step-by-step explanation:
The dimensions of the localizer full scale deflection for an Instrument Landing System (ILS) are typically ±1 degree of angular deviation from the centerline, which represents about 700 feet laterally at the threshold of a typical ILS runway. Inside these dimensions, the localizer provides precise lateral guidance to aircraft on the final approach path.
Beyond these dimensions, the localizer signal is considered unreliable, and pilots may see a "flag" on their cockpit instruments indicating that they are out of the acceptable range for guidance. This flag is commonly known as the OFF flag or localizer failure flag. Such indications are vital for a safe approach, informing the pilot when the aircraft is outside the recommended path and corrective action is needed.