Which instrument provides vertical guidance during an approach?

The Glide Slope Indicator is the instrument that provides vertical guidance during an approach, especially during an Instrument Landing System (ILS) approach. It indicates whether the aircraft is on the correct vertical path towards the runway. This is essential for precision landings, as it helps pilots to maintain the proper descent angle by providing real-time feedback on their altitude relative to the desired glide slope.

When flying an ILS approach, the glide slope provides crucial information that helps pilots manage their altitude and descent rate, ensuring they stay aligned with the ideal approach path. This vertical guidance is typically depicted on the aircraft's navigation display, showing whether the aircraft is above, below, or on the glide slope.

The other instruments mentioned serve different purposes: the Altitude Indicator displays the aircraft's current altitude, the Vertical Speed Indicator shows the rate of climb or descent but not where the aircraft should be in relation to the glide path, and the Heading Indicator provides information about the aircraft's current heading or direction, which is unrelated to vertical positioning during an approach. Thus, the Glide Slope Indicator is vital for ensuring safe and efficient landings in various weather conditions.