The ILS comprises localizer and glide path equipment and marker beacons, usually supported by a locator (NDB).
In the event of a locator (NDB) failure, aircraft must join the ILS outside the outer marker.
In the event of glide path failure, only localizer procedure is available.
When marker beacons are not available, ILS may be used provided alternate fixes nominated on the instrument approach chart or NOTAM are used for altimeter checks.