I'm studying for my instrument rating, and an airport where I've been practicing (KSTC - Saint Cloud, Minnesota) has an ILS approach for 31 (http://22.214.171.124/d-tpp/1110/05799IL31.PDF). The approach has the standard OM, and also has an LOM at the same location, which seems to be fairly typical.
What I don't understand is why the approach plate indicates, "ADF REQUIRED." With an outer marker, why would the approach require this? It's not needed for knowing the outbound course, since the localizer and outer marker would seem to tell you everything you need to know to fly it. What am I missing?