on the understanding that I need to be aware of the 25mile limitations and provide separation accordingly.
This has absolutely nothing to do with other traffic or separation.
Whilst most modern aircraft can indeed utilise B-RNAV systems to maintain the localiser course until within the protected range, the use of the localiser (and glide-path) outside the prescribed DOCs is incorrect and potentially unsafe and should certainly not be something that ATC routinely provides, offers or encourages.
If the PIC requests it, then ATC should issue an appropriate warning and leave it up to the flight deck to self-position, all responsibility then transfers to the aircraft's Commander.
Radar monitoring may well be a pragmatic and sensible course of action in such circumstances but ATC should never actively participate in the use of any ILS signal outside its DOC.
From the relevant UK AIC:-
2.1 ILS facilities in the United Kingdom conform to ICAO Annex 10 Volume 1, Radio Navigation Aids Standards and Recommended Practices (SARPs) appropriate to the promulgated Facility Performance Category. Where the UK has differences filed to the SARPs, these will be published in Supplements to the ICAO Annex and notified in the UK AIP General section GEN 1.7 - Differences From ICAO Standards, Recommended Practices and Procedures.
2.2 An ILS can therefore be relied upon to provide navigational information to the required accuracy providing:
(a) It is only used inside the specified coverage areas;
(b) the signal-in-space is being adequately protected by Air Traffic Control;
(c) due account is taken of any warnings or differences notified in the UK AIP or by NOTAM
2.3 An aerodrome's ILS facilities should only be used when an Air Traffic Control Service is available for the airport. No attempt should be made to use the ILS outside the aerodrome's promulgated hours of operation, unless specific arrangements have been made with the aerodrome operating authority for this purpose which include the provision of an Air Traffic Control Service.
3 Localiser 3.1 The standard ILS Localiser Designated Operational Coverage (DOC) provides coverage in the following overlapping areas.
From the centre of the Localiser antenna to distances of:
(a) 25 nm within plus and minus 10° of the front course line;
(b) 17 nm within plus and minus 35° from the front course line.
3.2 Where topographical features dictate or operational requirements permit the DOC may be reduced to the following coverage areas. From the centre of the Localiser antenna to distances of:
(a) 18 nm within plus or minus 10° of the front course line;
(b) 10 nm within plus and minus 35° from the front course line.
In these circumstances the coverage will be notified in the UK AIP Part 3 Aerodromes, AD 2.19 - Radio Navigation and Landing Aids, specific to that facility.
3.3 Flight crews are warned that use of the Localiser outside these coverage areas can lead to false course and reverse sense indications being received. Such use should not be attempted.
You have been warned...
