RUMBEAR has a point. In EASA-land, the use of 550 RVR for CAT I minima, as opposed to ICAO's standard of 750 m, is based on a set of conditions, and FDs are one of them. Except it is not AIP, but the operator's OM-A written i.a.w. applicable (pan-)national regulations. The didactical quality, as well as depth of understanding of OM-A, naturally vary.
The OP's question is very valid. According to my LIDO OM-C, the regulatory reference is AMC5 CAT.OP.MPA.110.
RVR of 750 m or less .... may be used
- for Cat 1 operations to runways with FALS, RTZL, and RCLL;
I only quoted the non-FDs section. My personal memory trick to remember is:
. CAT II lights > no FDs required
. Simple ALS > FDs are required