The constant march of progress always leaves old favourites by the wayside.
In the case of avionics, the retirement time may be close at hand for instruments we have been comfortable with for decades.
VORs, ADFs and DMEs have been overtaken by glass cockpits and GNSS.
It is not hard to imagine a time when they no longer figure in most flights, IFR or VFR.
Once the pinnacle of navigation, this level of technology is now often referred to as ‘steam-driven’, but it forms the basis of a valuable back-up system that will get you home when your GPS drops out - and as such still has a place in the cockpit.
Airservices Australia has effectively confirmed their secondary status by decommissioning many NDBs and VORs, leaving only enough to be useful in an emergency.
Initially, the back-up network was set to leave only 103 NDBs and 45 VORs active.
While a threadbare network like this is handy when things turn black, it will make day-to-day ops more challenging than before.
So if you are in a position where you need to do something with your old instruments, now is the time to think upgrade.
There are manufacturers still turning out new units, but your avionics engineer will most likely suggest settling for a second-hand system because the cost of new ones can be very close to the cost of a good GPS.
If that is the case, bolting in a new GPS might be the better option, as the best units include VOR/ILS capability anyway.
VOR
Garmin, Narco, Bendix King and Val Avionics still produce new VORs, generally in combination with a comm unit or, in the case of Garmin and BK, with the GPS.
The functionality is comfortably familiar, with only minor advances in the displays to differ them from what was on offer 15 years ago.
One change is that the OBS indicators are often integrated with the nav/comm rather than being stand-alone instruments.
The weight and cost saving is obvious.
For more information on these units, see the Nav/Comm section of this guide.
ADF
For most pilots, the Automatic Direction Finder would have been the first nav instrument they learned to use.
Even if the concept of wind correction did not sink in, simply flying at the Non-Directional Beacon would get you there, albeit via a somewhat circular route.
They are also good for tuning to AM radio and getting a cricket score.
But with the technology now in its declining years, new ADFs are getting hard to find and, if you insist on a new replacement unit, you will likely find yourself with a Bendix King KR87.
None of the other major manufacturers have an ADF in their range.
DME
DME navigation has been described as a dying science.
Since GPS was approved for en-route distance measuring, DME’s have largely been relegated to the training fleet, although stubborn survivors can be found in commercial and private aircraft.
As with the ADF, a new DME unit is also likely to come from Bendix King, with the KN63 still on offer. Other than that, the pickings are very slim indeed.