Are there any dual NDB approaches?

Bern used to have one. It even used 3 NDB’s if you count the GA fix. Shupberg, Muri and Berne. Flew it many times in the Seneca when doing my IR at the time.

I don’t know whether this qualifies as dual NDB approach.

Fly310 wrote:

But I do not know if there is a big difference on the maintenance side. If the NDB station requires less work at the ground station or not.

There is a big difference. An NDB station is just an antenna mast with a very simple transmitter. No particular siting requirements, the monitor needs only check that the station is transmitting at all. A VOR station is an entirely different beast with a much more complex antenna, seating requirement, transmitter and monitor.

Fly310 wrote:

During my training we only ever had one ADF on board which meant that you switched NDB frequency as soon as you had a 90 degree deflection on the needle and continued towards the next one.

In theory you would get better precision if you left the first NDB on a QDR and switched halfway to the next one. In practice, however…

Thanks for good explanations. Now that we mostly use GPS but still need redundancy I often wonder if it wouldn’t have been best to keep the NDBs instead of VORs because they seem so simple. But I do not know if there is a big difference on the maintenance side. If the NDB station requires less work at the ground station or not.

VORs were not suitable in USSR as these don´t have sufficient range in a huge country. So they had lots of NDBs and often two of them in line of runways at airports for “instrument approaches”. The ADF indicator clock was a combination of RMI and ADF pointers , no need for correcting ridiculous gyro direction indicators that you calibrate with the old alcohol compass with its crude scales in max. half hour periods. The sophisticated dual ADF system was controlled at a separate instrument for two NDB settings by a flip switch for two NDBs in line with runways. There were a few more devices for fine-tuning the system for taking care of certain effects but I don´t know details as our Yak still got the visible instruments for classic looks but miss some devices possibly after restoration in earlier life. There are some clips in YT about Russian ADF systems in simulator flights, avalable in English and German, showing the procedures on ARK 15 with two NDBs for approaches. Vic

blue arrow ADF/RMI indicator, orange arrow dual ADF controller:

Again, in Europe there are no more airports/airports that have only NDB approaches (only exception: Losinj, and that one is useless as well as the minima are high and you can approach VFR from the sea anyway, apart from the fact that nobody flies there if the weather is bad).

I have to correct you – Losinj has VOR approach as well.

The main advantage over a slingle NDB that it is very easy to fly; the indicator is a simple dual-needle RBI (not even slaved to anything like an RMI), you keep the needles overlapping each other. Very easy to intercept (fly towards the needles a 30 degree-ish heading, turn shortly before they converge) and to maintain track. It is immediately obvious if you drift to the left or the right, and you correct your heading accordingly. Much less mental effort than a single needle on an RMI.

The errors don’t really cancel out, for example coastal and terrain errors are the same, and with thunderstorms in the vicinity all bets are off as usual.