Originally Posted by ColoradoSolar
in my opinion VOR and ILS are one type of navigational aid since they are both VHF nav aids so just GPS should count.
VOR and ILS are quite different. VOR and Localizer frequencies are intermingled, making it easy for us to believe they are essentially the same technologies. Yes, they both work in the VHF band, but that's about where the similarities stop. The VOR signal is actually quite a complex signal if we take the time to examine how it is modulated to achieve the desired navigation outcome. Localizer, on the other hand, is a much less complex signal involving modulation with two different audio tones.
Additionally, for an ILS to function as an ILS there's that other component that comes into play, the Glideslope. Glideslope frequencies are typically invisible to us as a pilot because they are paired with Localizer frequencies, thus the GS receiver is magically tuned for us when we select a Localizer frequency which has an associated Glideslope.
Saying that VOR and ILS are one type of approach is, I believe, a rather critical over-simplification. A VOR approach is a very different beast as compared to an ILS approach or even a non-precision LOC approach.