What type of approach does ASR refer to?

ASR refers to Approach Surveillance Radar, which is a type of radar system used by air traffic control to provide guidance to aircraft during their approach to an airport. The primary function of ASR is to detect aircraft positions and help controllers provide separation and instructions to pilots as they approach for landing.

Unlike precision approach radar, which provides vertical and horizontal guidance for precise approaches to the runway, ASR does not provide glide slope information. Instead, it gives the aircraft's horizontal position and altitude, enabling controllers to vector aircraft on a safe path towards the runway. This method is particularly useful in conditions where visibility is low, allowing for a safer and more efficient traffic flow during landing operations.

The other options listed do not accurately describe the type of approach associated with ASR. Precision approaches are distinct from surveillance approaches as they offer more detailed guidance. The terms vertical approach radar and ground approach radar do not correspond with established radar categories used in aviation.