ADF frequency indication on ND

[Hardy Heinlin]

Good evening,

as we know, when there's no VOR signal in range, the ND indicates no morse ID and no frequency. The green text block just contains "VOR L" or "VOR R".

Should the ADF indication logic be similar?
Or -- when no NDB signal is in range -- should the tuned ADF frequency always be displayed?

And if so, could this be an airline option?


Regards,

|-|ardy

[John H Watson]

as we know, when there's no VOR signal in range, the ND indicates no morse ID and no frequency.

I didn't know this    What is your definition of "in range"?

I found a photo showing just "VOR L" no frequency  and a photo showing "VOR L and frequency" of a manually tuned station which was out of range (aircraft on ground, approx. distance to station 70nm). Same airline. However, as you may recall, there was some strangeness in my area due to the autotuning of an out-of-range TACAN.

(EDIT) I have a photo of a CDU showing blanks in the Left VOR slot. I don't know if this was due to TACAN autotuning or something else. I know you have a theory that both slots can be blank on an aircraft which has just been powered up, but I don't think I've seen this.

(EDIT 2) Just found a photo of the ND showing the autotuned out of range TACAN. The frequency is shown in small font. The CDU shows blanks.

Two out-of-range stations

[Hardy Heinlin]

My actual question is whether the ADF frequency should be always displayed when the ID is not decoded (and if so, whether it might be a software option).

I just mentioned the VOR system for comparison because there are many photos showing just "VOR L" or "VOR R"; this effect is a fact regardless of the causal theory behind it -- and at the moment I'm just unable to find similar photos regarding the ADF display. On all photos the ADF L or R text blocks always include an ID or a frequency.

[John H Watson]

On all photos the ADF L or R text blocks always include an ID or a frequency.

VOR, ILS or ADF manually tuned (with frequency) will always show the frequency irrespective of range. A manually tuned station may not be in the FMC database, so range may be unknown.

Perhaps range may become a factor if the station is tuned using an identifier?
(EDIT: ADFs cannot be tuned using an identifier)

[Hardy Heinlin]

By "in range" I meant "radio signal being received", i.e. the status when a traditional steam gauge instrument is alive.

Here's an inflight photo I took myself. It just shows "VOR R". Well, OK, it's certainly in autotuning mode.



(By the way, notice the left VOR ID "CEAE" -- four letters.)


|-|ardy

[John H Watson]

Interesting.

I have an old photo showing autotuned BIK VOR and RIC Tacan (out of range signal-wise from Sydney) which shows frequency.

BIK & RIC

Either it's an air/ground thing, or "in range" is based on actual distance (not reception).

[Hardy Heinlin]

Frequencies are now always displayed in the above case in PSX 10.76:

http://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

[John H Watson]

I just noticed in a video of a NAV RAD page, I have manually tuned frequency "SYm112.10" in the VOR R slot. I assume this was tuned by entering "SY" and not the frequency.

I have a radial display of 308, and dashes are shown in the CRS slot. I pull the CB for the Right VOR CB and about 3 seconds later, the radial display blanks completely, but the 3 dashes in the CRS slot remain in view (The video runs for about 18 seconds after CB's pulled). SYm112.10 remained in view after I pulled the CB.

Having the course entry available will still allow the pilot to draw a green dashed line on the ND as a reference. I assume if I entered the VOR using only its frequency, the dashes would disappear. In PSX, when I pull the CB, stations tuned using their ID lose their CRS dashes.

(EDIT: If you enter a VOR station using its ID and there are two stations with the same ID, does the FMC choose the closest one? If you also enter an associated CRS, and then fly from the closest station to the other station, what will happen?)

[Britjet]

The CEAE is most likely a false decode of the CEA NDB. It happens fairly frequently although I don't remember seeing 4 digits before.
Not sure about this freq display thing? Seems odd to display something that isn't working...
I should get the chance to check it in a couple of weeks.
Peter.

[skelsey]

I would guess that that frequency thing must be to do with the capability of the aircraft to decode the ident?

The ident comes from the Morse transmitted by the station, not the FMC navigation database (AFAIK). Therefore if a station is being received but the aircraft cannot deduce the ident (e.g. due to a weak signal/interference etc) then it would make sense to display the frequency only (and then the crew can listen to the audio ident).

If no station is being received and no frequency has been (manually) tuned however, then it would make sense to simply display 'VOR' (or 'ADF')?

[skelsey]

Further to the above:

According to the manual:

VOR L(R) or ADF L(R) indicates the position of the ADF/VOR switches.

Separately to that:

VOR frequency or identifier (G), ADF frequency or identifier (B)

Displays frequency before identifier is decoded. Decoded identifier replaces the frequency. For VORs, small size characters indicate only DME information is being received. Located in the lower left or right corner.

That would seem to support the theory that whether frequency or ident is displayed is dependent on the capability of the aircraft to decode the ident... but I'm struggling to come up with a situation where nothing is displayed.

Is there a situation where the autotune would 'park' a receiver?

[Hardy Heinlin]

It's not a theory, Skelsey, it's a fact :-) Indeed, the system gets the raw Morse audio signals and tries to decode them. After retuning it will always take some seconds until the decoding is completed. This delay is also modeled in PSX. NDB identifiers in the database cannot even be assigned to tuned frequencies as the FMC has no NDB frequency database.

The original question was just whether the frequency remains displayed as long as the audio is not decoded or as long as there is no radio signal at all.

[Dirk Schepmann]

Regarding the picture taken inflight:

I'm wondering why the VOR R is blank. If there is only one VOR in range (CEAE in this case), I would have expected that both radios are automatically tuned to that VOR.

Interesting, but it makes sense because it would not improve position accuracy.

[skelsey]

The original question was just whether the frequency remains displayed as long as the audio is not decoded or as long as there is no radio signal at all.

Hi Hardy,

Based on the observations that yourself and John have posted I am thinking neither.

The images have shown (at least VOR) frequencies displayed with the station out of range in both auto and manual tuning. My theory therefore is that the only time nothing is displayed (neither frequency nor ident) is if the receiver is 'parked' in some way (i.e. nothing is tuned - not just no reception on a tuned frequency). Of course, that would only be valid if the auto-tune function is capable of 'parking' the receiver and I have no idea if that is the case.

If it were true, however, the natural extrapolation from that would be that the ADF frequency is always shown as the ADFs are always manually tuned (so there will always be a definite frequency selected) and I don't think it is possible to 'park' them by clearing the entered frequency?

It will be interesting to see what Peter is able to discover on the sim!

Simon

[Hardy Heinlin]

I thought your theory was about the question whether the identifier display is derived from the database or from the radio audio. My answer just referred to that. (It's from the radio audio indeed.)

In version 10.76 the ADF frequency is now always displayed unless the audio is decoded. Same for VOR when manually tuned. It may disappear when autotuned and not in range.


|-|ardy

[skelsey]

Indeed - I think I sidetracked myself by going down that particular path earlier!

[John H Watson]

I'm wondering why the VOR R is blank. If there is only one VOR in range (CEAE in this case), I would have expected that both radios are automatically tuned to that VOR.

There's a navaid flow chart in the following post (from when I was trying to figure out this stuff before).

http://aerowinx.com/board/index.php?topic=4164.msg44377#msg44377

The terminology is confusing, though.

http://www.members.iinet.net.au/~b744er@ozemail.com.au/744er/AutotuningLogic3.GIF

The notes in the bottom left hand corner suggest there should be something in the right slot.

What determines if a station is Route Tuned? Is it determined by something programmed into the Company Route? Or is it just determined by waypoints in the route and the coincidental availability of navigation stations in that route?

Can someone make that chart fit the photograph? I see quite a few stations in that area (including KHR, RRC, RAJ, BBS)

Situ file (starting in general area):

Autotuning CEA zip file

[Hardy Heinlin]

What determines if a station is Route Tuned?

FCOM: "R (route autotuning) - FMC selects navaids on the active route. The navaid is the previous VOR or a downpath VOR within 250 nm of aircraft position"

If you want to fly to or from a VOR, it makes sense to prefer that over an off-route VOR.


|-|ardy

[John H Watson]

Thanks. I wasn't sure of the accuracy (single VOR/DME versus two off-track DMEs).

[mark744]

Not quite the question being asked, but possible reason for lack of ADF frequency display on the ND........

I believe that on power up, the CDU ADF frequecies are blank (or dashes).
Therefore, if no manual entries are subsequently made, I assume nothing will be displayed on the ND.

I will try to check in the next few days.

Regards,

Mark.