How can I add (in FMC) outer marker OM and inner marker IM waypoints along the ILS track? They are often referred to in airport charts.guro75

Keep your eyes off the map and on the PFD. Those markers all emit sounds that can be picked up by turning the volume knob marked as MARKER or MKR on the radio stack. That way, you can just hear you're passing them as you fly over them, instead of having to look away to check. Occasionally, the OM will have another name to it (if it's a LOM), which you can just enter as you'd enter any other fix/VOR/etc.

It's not really required anymore, especially with the NG with LNAV and Radar Altimeter. I haven't hit too many tiny airports in a while, but I haven't needed to use a OM or MM or IM ever on the 737. In any case, you really wouldn't be putting those on the ND, RW.You might be interested in checking out how the ND and the Legs pages depict various fixes: Marker beacons – a marker beacon is identified by the marker type identifier followed by the runway number. Examples: • Outer Marker 13R = OM13R • Middle Marker 21 = MM21. Runway–related fixes – waypoints located at unnamed runway–related fixes are identified by adding a two–letter prefix to the runway number. The following list is used to determine the appropriate prefix: Examples: OM25L, MM09, IM23, RW04, RW18L. • RX – runway extension fix • FA – VFR final approach fix • CF – final approach course fix • FF – final approach fix • IF – initial approach fix • OM – outer marker • MM – middle marker • IM – inner marker • BM – back course marker • MD – minimum descent altitude • A – (+ an alpha) step down fix • RW – runway threshold • MA – missed approach point other than RW • TD – touchdown point inboard of RW.

How can I add (in FMC) outer marker OM and inner marker IM waypoints along the ILS track? They are often referred to in airport charts.guro75

FYI: Concerning the OM audible signal, in the US many of these facilities are being decommissioned given the new navigational technologies.