What next ?
The NDB's are disappearing and we are soon to see the same happening to the VOR's but it seems to me that the future is bleak for GA with IFR navigation all being done by GPS.
Some might say that with the European GPS system we have two systems available however both are easy to attack and a ground based navigation system is required so as most ILS systems have a DME attached it would seem like a good idea to do as the airlines have and mix DME data into the navigation plot. Most modern FMC system have this GPS, DME mix ( the B737 NG has five DME's three of them permanently attached to the FMC).
It would seem to me that the answer is for someone to make a DME/GPS interface that can feed the multi DME position into the aircrafts GPS unit, the pilot would navigate in exactly the same way as when using a GPS the only difference being that the position of the aircraft is determined by a mix of GPS & or DME data. The loss of GPS or DME data would not effect the navigation in any way.
OH !! It slipped my mind such a unit was available to the GA pilot but we were all to obsessed with the new and cheap GPS units to see the advantages and robustness of the multi-sensor navigation system, NARCO remember them? Made a thing called the STARNAV it had within the box GPS, VOR & ILS but also connected to DME and used a mix of GPS, VOR & DME to fix the aircrafts position and you could also feed a remote LORAN into the mix!
It would seem to me to be time to revisit the NARCO STARNAV concept to provide a more robust GA navigation system, it should not be to hard to do, I would think that a remote double DME unit could feed position data into the curent crop of GPS units via the data ports and most of us would not even know it would be fitted!