What does the middle marker (MM) approximately indicate?

The middle marker (MM) is an important navigational aid used primarily in instrument landing systems (ILS). It indicates a specific point along the approach path to the runway, marking the location where the aircraft is approximately 3500 feet from the runway threshold. This information is crucial for pilots, as the MM provides a reference that helps them gauge their distance from the runway while descending during the approach phase of landing.

In practice, when aircraft reach this point, they can expect to be in a position to safely land soon, allowing for necessary adjustments in their approach. The distance of 3500 feet from the runway aligns with standard procedures and guidelines for landing approaches, reinforcing the reliability of the MM as a critical marker on approach.