If the first letter identifier of a localizer is 'X', what does this signify?

When the first letter identifier of a localizer is 'X', it indicates that the alignment of the localizer is significantly off. Localizers are part of the Instrument Landing System (ILS) and are used to provide lateral guidance to pilots as they approach a runway. The use of 'X' as the first letter in the identifier serves as a warning to pilots that the localizer beam may not be accurately aligned with the runway centerline, which could lead to misguidance during an approach. This essential information is critical for ensuring safety during instrument approaches, as it alerts pilots to exercise caution and not rely solely on that localizer for guidance.

Other identifiers are typically used to indicate unverified or non-standard conditions, making the 'X' a significant marker for pilots to reassess their approach strategy.