It is my understanding that the ILS beam quality may not be suitable for automatic landings on all CAT I installations. Deficient beam quality combined with an unusual terrain profile could lead to less than optimal autoflight performance that could occur at an altitude that may make timely corrective action problematic.
Below is an excerpt from the FCOM Autoflight Limitations section, which I have seen for a variety of current models of Airbus aircraft. I know of one operator that only permits automatic landings on CAT II/III ground installations. This is because they do not want to take the time to evaluate CAT I ILS beam quality at each airport. I would be interested in learning how other operators are dealing with this issue.
The Kid
AUTOMATIC LANDING IN CAT I OR BETTER WEATHER CONDITIONS
The automatic landing system’s performance has been demonstrated on runways equipped with CAT II or CAT III approaches. However, automatic landing in CAT I or better weather conditions is possible on CAT I ground installations or on CAT II/III ground installations when ILS sensitive areas are not protected, if the following precautions are taken:
• The airline has checked that the ILS beam quality, and the effect of the terrain profile before the runway have no adverse effect on AP/FD guidance. In particular, the effect of terrain discontinuities within 300 meters before the runway threshold must be evaluated.