Question 3-70K5

The localizer beam system provides horizontal guidance for aircraft approaching a runway. **D) Produces two amplitude modulated antenna patterns; one pattern with an audio frequency of 90 Hz and...** is correct. The localizer transmits two distinct amplitude modulated (AM) patterns. One pattern, typically to the left of the centerline, is modulated with a 90 Hz audio tone, and the other pattern, to the right, is modulated with a 150 Hz tone. An aircraft receiver compares the "depth of modulation" of these two signals; if the 90 Hz signal is stronger, the aircraft is left of centerline, if 150 Hz is stronger, it's right. Equal strength indicates the aircraft is on the runway centerline. **A) Operates within the assigned frequency range of 108.10 to 111.95 GHz** is incorrect. Localizers operate in the Very High Frequency (VHF) band, specifically from 108.10 to 111.95 **MHz**, not GHz. GHz indicates microwave frequencies, which are much higher. **B) Produces two amplitude modulated antenna patterns; one pattern above and one pattern below the normal** is incorrect. This describes the operation of the **glide slope** system, which provides vertical guidance with signals transmitted above and below the desired glide path. The localizer provides horizontal guidance. **C) Frequencies are automatically tuned-in when the proper glide slope frequency is selected on the aircraft’s** is incorrect. While localizer and glide slope frequencies are paired for convenience, typically the pilot selects the desired **localizer** frequency, and the corresponding glide slope frequency is automatically tuned by the aircraft's avionics. The statement also ends abruptly.