Just an FYI for those more curious about whether or not you can auto land on any runway. as previously stated not all runways are able to support landings down to minimal lower than CAT 1 (typically a cloud base 200’ above the deck and a visibility of 550m). This can be the capabilities of the ILS equipment, runway geometry, local terrain, runway lighting, ability to have interrupted power (Gatwick lost it’s CAT2/3 capability for about a month one deep fog season due to a flooded substation knocking out the back up generator redundancy). Typically most major intl airports have CAT3B capability ILS systems when not constrained by the above limitations.

Next is the aircraft. For example not all EMB190s flying are CAT3B capable, some are just 3A and manually flown. The same for 737s. Some operators will not pay for the maintenance require vets and certification costs of what is known as ‘dual channel approaches’. Whist the aircraft is certified, the carrier chooses not to utilise the absolute lowest possible minima due to cost.
then there are carriers that do have all of that in hand but other allowable defects temporarily stop the aircraft from being capable of using its worst weather potential.

On top of all this is crew qualification. If a pilot is unable to re-qualify for low visibility operations during recurrent sims then they can’t conduct those approaches below CAT1 weather. New commands (captains) are also restricted for a short period to allow them to settle into the aircraft on completion of training prior to being permitted to conduct a low vis approach. There have been multiple news stories on this over the years. A story of a GO flight and also Flybe come to mind.

So in short all three elements are required.