When NAV 1 is tuned to a valid ILS frequency, which indications will the ISI display?

When NAV 1 is tuned to a valid ILS frequency, which indications will the ISI display?

• A. Localizer deviation only
• B. Glide slope deviation only
• C. Localizer and glide slope deviation
• D. No deviation

Answer: (C)

When NAV 1 is tuned to a valid ILS frequency, the receiver locks onto both signals that ILS provides: the localizer for horizontal guidance and the glideslope for vertical guidance. The ISI is designed to show deviation for both channels, so you get lateral deviation from the localizer and vertical deviation from the glideslope. This dual feedback lets you fly the approach along the centerline and on the correct descent path at the same time, which is why both localizer and glide slope deviations appear on the ISI.

When NAV 1 is tuned to a valid ILS frequency, the receiver locks onto both signals that ILS provides: the localizer for horizontal guidance and the glideslope for vertical guidance. The ISI is designed to show deviation for both channels, so you get lateral deviation from the localizer and vertical deviation from the glideslope. This dual feedback lets you fly the approach along the centerline and on the correct descent path at the same time, which is why both localizer and glide slope deviations appear on the ISI.