ILS accuracy factors and what degrades them?

• A. Multipath and improper installation can degrade ILS localizer and glideslope accuracy.
• B. Weather is the primary factor for ILS accuracy.
• C. Interference does not affect ILS.
• D. Multipath improves accuracy.

Answer: (C)

ILS accuracy depends on clean, properly patterned signals from the localizer and glide slope. The two main degraders are multipath reflections—signals bouncing off the runway, ground, or nearby structures and arriving at the receiver at different times— which distort the perceived horizontal and vertical guidance. Improper installation or misalignment of the localizer and glide slope antennas also degrades accuracy by offsetting the transmitted patterns from the true centerline and glide path. Weather isn’t the primary factor affecting ILS accuracy because the system’s line-of-sight VHF/UHF signals are not significantly altered by typical atmospheric conditions. Interference can degrade ILS readings, so the idea that interference doesn’t affect ILS isn’t correct. Multipath, in particular, is a form of interference that reduces accuracy rather than improves it.