On an ILS approach, with approch mode amed while you are slightly below platform altitude, things should be okay correct?
I'd say so.. but still need to be cautious of your speed and configuration (it might not work if you are clean, 20 kts tailwind and at 290kts..)
Having said that, do you mean platform altitude?
If you are cleared to descend 3thousand and also cleared for the approach, you shouldn't be going below the platform of 3thousand until you have captured the glide.
If you are above platform altitude, wether or not you will catch the glide depends on distance.
If you were at 4500 feet on long final 17 miles, you should catch the glide correct?
If you were at 10 miles (for example), you'd have to catch it from above.
Is the GS usually accurate if showing you that you're above or below it, even from a far distance?
It's roughly the 3x table.
2000ft - 6 miles, 3000 - 9, 4000 - 12 etc
You of course need allowance for the airfields height above sea level.. if threshold elev is 12 feet it doesn't matter, but if it is 1800 feet then your readings on the altimeters are going to be higher and you may get caught out with configuration etc.
As mentioned above, you have areas of coverage for the ILS. Caution when intercepting from above due to false glide paths etc, if it is IMC then you need to be really careful about this.. one of the reasons we have a check height on the way down (usually the OM or alike).
Also. If you were coming 15 miles from touchdown, and 3000 feet, with a platform altitude of 2000 feet. You are coming from the opposite side of the runway, and ATC has cleared you for the approach (hypothetically), in this case surely the GS will never bring you down coming in from that angle correct?
Don't understand that?