Dodgy ILS signals

The SBO out failure mode is pretty bad, there’s nothing in the signal to detect it, it looks perfectly like an on-glide signal. The only way to detect it is via cross checks to other glide information sources, be it the FAF check (but then you have to look for the glide slope indicator approaching from above), or DME/baro height, or GPS derived glide slope…

I thought ILS signals were monitored on the ground as well, with dedicated (and calibrated) monitoring tools? If the signal fails or is outside parameters, the ILS is supposedly shut down, or at the very least ATC is informed?

That doesn’t absolve the pilot from any and all responsibility to monitor and cross-check things of course.

I thought ILS signals were monitored on the ground as well, with dedicated (and calibrated) monitoring tools?

Yes … but watch the video.

A good check is to always verify that there is movement of the GS indication. If you intercept from below the GS and don’t have a fly up indication followed by the GS centering at the appropriate approximate distance from the runway, then you should be extremely suspicious and miss the approach. The sequence should include GS alive, fly up indication followed by GS centered at the correct distance from the runway. If your first indication is GS centered, then either you were vectored too close for a proper approach, you missed the GS alive and movement, or there is a system problem in your aircraft or in the ground equipment. Any of these justify missing the approach.