Which system helps pilots land using instruments?

The Instrument Landing System (ILS) is crucial for pilots when landing in low visibility conditions. It provides precise guidance to aircraft approaching a runway through radio signals and, in many cases, visual aids. The system comprises two main components: the localizer, which aligns the aircraft with the runway centerline, and the glide slope, which helps maintain the correct descent angle. This capability enables pilots to safely land aircraft using instruments rather than relying on visual cues, which is critical during fog, rain, or at night when visibility is significantly reduced.

Other systems listed, while they may aid in different aspects of flight, do not specifically provide the comprehensive instrument approach capabilities that the ILS offers. For example, Digital Resolution System and Controlled Descent System do not focus on instrument-based landings, and while the Precision Approach System pertains to approach stages as well, it does not specifically refer to the widely recognized ILS framework. Thus, the ILS remains the standard system for instrument-guided landings, making it the correct answer.