The 500ft precision and 600ft non-precision absolute minima apply to IMC rating holders and are mandatory and the ANO says so.
Article 49 clearly says that pilots of non-public transport aircraft are not to descend below the notified minima unless the required visual references are established and maintained.
Notified means: Information set forth in a document published by or with the authority of the CAA and entitled Supplement (NOTAM)
or AIP and for the time being in force. (my emphasis).
AD 1-1-6 of the AIP is very clear saying that "This section of the AIP specifies the notified method of calculating Aerodrome Operating Minima (AOM) for the purpose of
Article 39 (Public Transport Aircraft not registered in the United Kingdom) and Article 40 (Non-public Transport Aircraft)."
(The article numbers were changed in the last ANO amendment.)
The AIP goes on to say;
3.3.2 IMC Rating Holder in Current Practice
3.3.2.1 Pilots with a valid Instrument Meteorological Conditions (IMC) Rating are recommended to add 200 ft to the minimum
applicable DH/MDH, but with absolute minima of 500 ft for a precision approach and 600 ft for a non-precision approach. The UK IMC
Rating may not be valid outside UK territorial airspace, therefore IMC Rated pilots should check the validity of their rating for the State
in which they intend to fly. If the rating is not valid pilots must comply with the basic licence privileges, subject to the regulations of that
State.
To put that in simple terms;
The ANO says that pilots must comply with Notified minima. Notified means published in the AIP or NOTAM etc and the AIP says that the 200ft addition is advisory but that the absolute minima of 500ft precision and 600ft non-precision are mandatory.
That is the legal basis and that is why they are mandatory and why they are in the exam still.
Thus ILS with 200ft DH will mean 500ft DH legal minimum for an IMC holder.
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As for FM immune requirements.
There is a very simple way to think of the FM issue pertaining to ILS and VOR equipment. If it is not FM immune it is U/S.
If you would not rely on a U/S instrument or navigation system to navigate in IMC or make an instrument approach in IMC then you would not use a non-FM immune system.
DME and ADF are not limited by the requirements. Thus I would not see a probem with flying to a destination in class G airspace where the approach would be an NDB or NDB/DME and if required by law, the alternate also had an NDB or NDB/DME procedure available. eg Blackpool.
However, regardless of airspace, flying an ILS or VOR procedure with U/S equipment would be illegal.
There is no law that says one can not fly an aircraft in VMC using visual navigation while looking at the indications on an unserviceable ILS or VOR indicator. That is the legal basis of IMC training in VFR - the instructor is visual and navigating visually and can ensure the safety of the aircraft.
People are silly to pay for training with U/S equipment even if it is for the IMC rating. Many operators have used FM immune as an excuse to push up prices but never fitted the equipment.
Regards,
DFC