Which substitution is appropriate during an ILS approach when the glide slope becomes inoperative?

When conducting an Instrument Landing System (ILS) approach, if the glide slope becomes inoperative, the appropriate action is to use the localizer (LOC) minimums instead of the regular ILS minimums. This is because the localizer provides lateral guidance, allowing the pilot to maintain the correct runway alignment, but without the glide slope guidance for vertical descent.

Using localizer minimums recognizes that although vertical guidance is lost due to the inoperative glide slope, the pilot can still execute a straight-in approach to the runway by following the beam provided by the localizer. The localizer minimums are established to ensure that altitudes and visibility requirements are met while solely relying on lateral navigation.

While VOR, GPS, and standard minimums could theoretically be used, they do not provide the same level of precision for an approach that relies solely on lateral alignment under the conditions where glide slope information is unavailable. Ensuring adherence to localizer minimums maintains safety during the approach, utilizing the available equipment effectively to land safely.