Some ILS proceedures have Outer Markers, others dont. For those that do, a failed OM without a published equivalent position or SRE/PAR fix means the proceedure is 'Not Allowed'. At least thats my reading of the books.
Why is this ? What criteria determines the necessity of the OM in the first place.
It seems strange that in places like Holland, Belgium, Northern Germany for example, where the terrain is as flat as a pancake, for those approaches with an OM specified, the lack of it (ie. U/S) eliminates an otherwise useable ILS approach. In contrast, in other places with quite rugged terrain in the vicinity there are ILS's without OM's.
Just curious, as it seems inconsistent.
