What is the purpose of the inner marker (IM)?

The inner marker (IM) is specifically designed to indicate the decision height point for Category II and III instrument approaches. When pilots are conducting an approach in these conditions, the IM provides critical information about when they must decide whether to continue the landing or execute a missed approach based on their altitude and visibility.

This function is particularly important for approaches with low visibility and precision, allowing the pilots to make informed decisions at specific altitudes. The presence of the inner marker helps ensure that the flight crew can maintain safety standards by providing a clear point for decision-making during the landing process.

The other options pertain to different aspects of navigation and approach processes, but do not accurately describe the primary function of the inner marker as it relates to decision height in low visibility landings.