What is a false glideslope?

A false glideslope occurs when a pilot receives misleading vertical guidance during an approach due to reflections of the glideslope signal. The correct answer identifies this situation as being related to the 150 Hz frequency being reflected above the 90 Hz lobe of the glideslope system. Essentially, this reflection can create the illusion of an alternate, incorrect glideslope that could lead to a dangerous situation if the pilot mistakenly follows it instead of the actual guidance.

Understanding the mechanics of a false glideslope is crucial for pilots because it can lead to accidents during the critical phases of approach and landing if not recognized and managed properly. Addressing the other choices helps clarify how they don't define a false glideslope; incorrect altimeter settings pertain to altitude indication, software errors on the Primary Flight Display (PFD) would affect the presentation of information but not directly relate to glideslope signal distortion, and temporary loss of signal from the glideslope antenna results in a complete lack of guidance rather than the misleading guidance that defines a false glideslope.