Originally Posted by
Bullethead
Another point worth considering, some ILS approaches don't have an outer marker beacon with which to make a glideslope height check and so use a DME/height check instead. If the DME is U/S then the approach, ILS or LLZ, can't be used.
Not necessarily true. Here in Canada and the U.S. if the DME is u/s an aircraft can use an appropriately approved GPS unit using a DME waypoint retrieved from a current database as a substitute for an unserviceable(or serviceable DME) waypoint based on DME.