What is a correct statement about the localizer beam system used during ILS approaches?

The localizer beam system is a crucial component of the Instrument Landing System (ILS), specifically designed to provide lateral guidance to aircraft as they approach the runway. A correct statement about this system is that it produces two amplitude-modulated antenna patterns.

This feature is significant because the localizer uses a pair of antennas spaced horizontally at the end of the runway. These antennas transmit signals that create a directional beam. The difference in the amplitude of the signals received by the aircraft's receiver indicates whether the aircraft is to the left or right of the runway centerline. This two-pattern system allows pilots to accurately align the aircraft with the runway as they descend, ensuring a precise approach.

In terms of the other options, while the localizer does indeed provide information critical for landing, it does not produce a constant signal, nor does it show vertical deviation from the runway centerline, as that function is specifically the work of the glideslope component. Additionally, the localizer system utilizes two frequencies, typically one for each of the two antennas, rather than just a single frequency for overall guidance, ensuring the accuracy and reliability of the landing approach guidance.