The Instrument Landing System (ILS) is accurate and reliable, but the ILS antenna design today causes secondary glide slopes to appear above the primary glide slope. Flight crews must be aware of this phenomenon to prevent unwanted aircraft behavior during an ILS glide slope capture.
This article explains the phenomenon of secondary glide slopes and their effect on aircraft systems. It provides guidance and examples that show how flight crews can prevent capturing a secondary glide slope. It also describes the protections on Airbus aircraft that limit the effect of an unintended secondary glide slope capture on the aircraft trajectory.
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