Choose the only correct statement about the localizer beam system used by aircraft to find the centerline of a runway during an Instrument Landing System (ILS) approach to an airport. The localizer beam system:
• ILS localizer vs. glideslope – what each one does and how they’re transmitted • Typical ILS frequency band (is it MHz or GHz?) • How 90 Hz and 150 Hz audio modulation are used in ILS signals
• Which ILS component (localizer or glideslope) relates to vertical guidance, and which relates to lateral (centerline) guidance? • Think about where aircraft radios are normally tuned for ILS – are they in the VHF MHz band or in the GHz microwave band? • How does the receiver know if the aircraft is left or right of centerline – what role do different modulation frequencies play?
• Verify the usual numeric range and units (MHz vs GHz) of ILS localizer frequencies in standard avionics references. • Confirm whether the two-lobe, above/below glide path description applies to the glideslope or the localizer. • Check how paired frequencies work in ILS (selecting one frequency and automatically getting another).
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