How is a "glide slope" defined in instrument approaches?

The definition of a "glide slope" in instrument approaches specifically refers to the electronic guidance system that offers vertical guidance during the landing phase of an aircraft approach. It is a critical component of the Instrument Landing System (ILS), helping pilots achieve the correct descent angle towards the runway.

The glide slope provides a precise path (typically set at a 3-degree descent angle) that pilots must follow, allowing them to align themselves vertically with the runway on approach. This vertical aspect is vital for maintaining a safe descent profile, especially in low visibility conditions where visual references are limited.

Other options do not accurately describe the glide slope. The first choice describes horizontal navigation, which is more about lateral guidance provided by systems like the localizer. The third option discusses airspeed maintenance, which is related to descent rate but not specifically tied to the glide slope. Lastly, radar used for approach control refers to different systems used to track and manage aircraft during approaches, rather than the vertical guidance provided by the glide slope. Thus, identifying the glide slope as an electronic system that provides vertical guidance is essential in understanding its role in instrument approaches.