Try this as a basic guide.
Both aircraft and airport have to have the necessary approved and calibrated equipment and the crews have to be so rated.
In the case of the 111c ILS, I think it is correct to say that the auto pilot/auto throttle must be able to bring the aircraft to a stop on the runway.
The aircraft in a Cat 111c approach may then have to wait, in conditions of extremely poor visibility, for a 'Follow Me' vehicle. This is of course becoming less of a necessity as ground radar is installed at certian airports, to the rage of local inhabitants who remain convinced that sterilisation awaits them.
* Category I - A precision instrument approach and landing with a decision height not lower than 200 feet (61 m) above touchdown zone elevation and with either a visibility not less than 2,625 feet (800 m) or a runway visual range not less than 2,400 feet (730 m), (with touchdown zone and center lightning, RVR 1,800ft). An aircraft equipped with an Enhanced Flight Vision System may, under certain circumstances, continue an approach to CAT II minimums. [14 CFR Part 91.175 amendment 281]
* Category II - Category II operation: A precision instrument approach and landing with a decision height lower than 200 feet (61 m) above touchdown zone elevation but not lower than 100 feet (30 m), and a runway visual range not less than 1,200 feet (370 m).
* Category III is further subdivided
o Category III A - A precision instrument approach and landing with:
+ a) a decision height lower than 100 feet (30 m) above touchdown zone elevation, or no decision height; and
+ b) a runway visual range not less than 700 feet (210 m).
o Category III B - A precision instrument approach and landing with:
+ a) a decision height lower than 50 feet (15 m) above touchdown zone elevation, or no decision height; and
+ b) a runway visual range less than 700 feet (210 m) but not less than 150 feet (46 m).
o Category III C - A precision instrument approach and landing with no decision height and no runway visual range limitations. A Category III C system is capable of using an aircraft's autopilot to land the aircraft and can also provide guidance along the runway surface.
The above is from the internet and is copied in here with no promise that it is absolutely up to date. In the case of any ILS approach other than a Cat 1, there is a requirement that the airport in question will implement certain ground orientated safeguards, hence Cat 11 holding points for departing aircraft to minimise distortion to the ILS glide path?
