EFIS/Nav Freq error on NG?

[Guest JTH]

Hello, I was trying to fly Timothy Metzinger's V2 tutorial 1 in the 737-700 today. Anyways, at one point he says to select "APP" mode for the ND on the EFIS. I have the ILS for the airport tuned in the radio panel, but when I turn the dial to "APP", I get an error on the ND: EFIS/Nav Freq Error, it says. Does anyone know why this is?Also, could someone possibly briefly explain what ADF is? The tutorial calls for you to turn on ADF, which is a little arrow that appears on the ND but I have no idea what it is or how it works.Thanks a lot in advance for any help! Paul.

[basa 0]

ADF is for Automatic Direccion Finder, which is tuned to NDB (Non Directional Beacon) stations. Is an old and simple, but still used, navigation system. It does not permit to fly a track (like VORs do). You can fly to a NDB station with your aircraft ADF, but unable to introduce wind correction. So if some wind is present you will fly a curved path (The dog's curve).You can also use radio broadcasting stations as NDB stations.Jose Luis

[Guest JTH]

So, does the outer marker (which represents the start of the ILS right?) at the same point as the NDB? If I understand it correctly then, the ADF arrow was pointing to the outer marker, aka the start of the ILS. Please correct me if I'm wrong in this though.And if you or anyone else can help me establishing why the above error happened when I went into "APP" mode on the ND it would be much appreciated.

[dave_paige 11]

Hi Paul;I suspect that the reason for the first error is that although you may have dialed in the frequency on you nav radio it may not have been the active frequency. You have to be sure that not only do you dial in the correct frequency, but, that you also make sure it's on the left side of the radio as the active frequency. I always tune in the ILS localizer frequency and make it active on both nav radios.The ADF is a radio reciever on your radio panel which can be tuned to non directional beacon (NDB) transmitters on the ground. Once that is done you can display the ADF needle on the ND by turning one or both of them on on the EFIS panel. The needle always points to the transmitter station. NDBs can be anywhere but in this case your are correct that the NDB is on the ILS course.

[basa 0]

The marker beacons in ILS systems (outer, medium and inner) are not for directional guidance. They broadcast very narrow vertical morse signals, and their mission is only for position-distance reference when you are stablished on the ILS localizer.Some approaches can use NDBs as fixes, but NDBs and marker-beacons are fully independent.And yes, make sure you not only dial the frequency but make it also "active" (green-yellow light)Jose Luis.

[downscc 1,327]

"So if some wind is present you will fly a curved path (The dog's curve)"Jose: The technique that used to be taught to fledging instrument rating students called for adjusting an angle to the desired bearing to stop wind drift. On a good day (full breakfast and steady winds), one could fly a string of decreasing S-turns until a relatively straight course was achieved to/from the NDB. My instructor pilot was pretty insistent that I learn how to do it, spent lots of time somewhere in Nebraska flying under the hood learning the art. I would have never earned his endorsement for the checkride if I flew a curved path.

[basa 0]

Thanks for your explanation Dan. This is what I like of this forums, you always are learning new things. And...well I should buy some modern manuals about NDB flying, perhaps the ones I have are as old as the NDB system itself.Jose Luis.

[ronzie 21]

There are some nice nav tutorials at www.stoenworks.com.Go to the Aviation section, clck on turorials.Here is the specific link to NDB approaches:NDB (ADF) Approaches: How to fly NDB (ADF) approaches. How to correct for wind drift. How to do Procedure Turns.http://www.stoenworks.com/Tutorials/IFR%2C...Approaches.htmlSee if that works for you.

[Guest JTH]

Hi thanks for the info. A few follow-up questions. Ok, firstly why are there TWO ADF switches on the EFIS, why not just one? Second, how often are NDBs used in modern jet flying in the likes of the NG? What I mean is, okay in this instance the NDB was helpful because it was also on the outer marker. But in other instances, would an NG pilot probably not use NDBs at all?And just a follow-up as to why I got the error, the ILS was tuned to ILS number one so I'm still unsure why it didn't work but may try the flight again and see if it works second time around. Thanks a lot once again for the continued support!

[Guest tmetzinger]

>The marker beacons in ILS systems (outer, medium and inner)>are not for directional guidance. >>They broadcast very narrow vertical morse signals, and their>mission is only for position-distance reference when you are>stablished on the ILS localizer.>>Some approaches can use NDBs as fixes, but NDBs and>marker-beacons are fully independent.>>And yes, make sure you not only dial the frequency but make it>also "active" (green-yellow light)>>Jose Luis.>Sometimes you have a marker beacon colocated with a traditional NDB - as is the case at KTNT. Markers do not have a frequency that you can tune on an ADF, but of course the colocated NDBs do.I used the colocated NDB at KTNT in my tutorial as it would allow a pilot to find his way to the final approach fix even if he was otherwise lost, and enhance spatial awareness.-Tim