A non-FM immune ILS or VOR system is U/S. Put another way, it no longer meets the required standard for it to be used as intended.It is not sensible or legal to use U/S equipment as a sole source of navigation information on an IFR flight.
Out of interest, is it only the UK / Europe which insists on FM Immunity? Does this mean that my 00's of approaches done in N registered aeroplanes in the US have been dangerous?
The FAA say that you no longer need to carry paper charts in a suitably equipped aeroplane (G1000 etc....). I did have a reference but can't find it at the moment, so don't ask me for it
