What is the maximum allowable error for an ILS localizer check?

The maximum allowable error for an ILS localizer check is +/-4 degrees. This figure is established to ensure that the localizer system provides sufficient lateral guidance to help pilots accurately align with the runway during an approach. The localizer is a critical component of the Instrument Landing System (ILS), providing precise direction to pilots. If the localizer was to exhibit an error greater than this threshold, it could lead to a misalignment that compromises the safety and accuracy of the approach, potentially leading to dangerous situations during landing.

The configuration and performance requirements for an ILS localizer are specifically designed to enhance the reliability of the instrument approach, thereby lending itself to a standard of +/-4 degrees to account for potential discrepancies while maintaining safety margins during approaches.