FMC nav radio page

[Jeroen Hoppenbrouwers]

Correct. The open question is what happens on the CDU (NAV RAD) after the ND and PFD swap from frequency to decoded ID. We assume it will still show the originally entered ID. And we need real-world 744 input to know this for sure (unless I missed a message somewhere that it had been observed and confirmed).


Jeroen

[John H Watson]

In Sydney, Australia, entering "MGM", a VOR in the USA (with the freq 112.10), on the Nav Rad page, the CDU will always show MGM, but the ND will decode and show SY (a local Sydney VOR with the same frequency)

Is that what we are trying to confirm?

First the freq appears on the ND, then the ID of the local DME in small font, then the ID of the VOR in large font.

Regards

[JRBarrett]

Another factor to consider. Here in the U.S., it is standard practice to temporarily disable the broadcast of the 30-second morse ID from a VOR which is known to be malfunctioning in some fashion, or even suspected of having a malfunction.

This could happen under several scenarios, such as: (1.) FAA ground facilities maintenance engineers may be at the VOR transmitter site, performing scheduled or unscheduled repair work or calibration of the VOR transmitter. (2.) The VOR's own self-diagnostic systems have detected a problem, i.e. transmitted power has decreased below a certain threshold, the transmitted carrier frequency has drifted outside of allowable limits, the modulation of the RF carrier is too low, or too high etc. Any of these problems could cause inaccurate navigational performance in aircraft using the VOR.

For this reason, when I was training for my instrument rating, my instructor emphasized that the pilot should ALWAYS monitor the audible morse code ID of a given VOR when first tuning the NAV receiver. Not only to insure that the correct VOR is being received, but also to insure that the ID is in fact present - if no ID is heard within 60 seconds, one should assume that there is a problem, and any indications of course or bearing should be considered suspect. Likewise, the instructor insisted that I should audibly monitor the ILS localizer morse ID continuously throughout an ILS approach - to insure that the proper localizer was actually in use. (My home airport, like many, has one primary runway, with an ILS at each end - the two localizers have the same frequency - but the morse IDs differ between the two ends.

Does the 747 FMS have the logic to deal with a missing (as opposed to incorrect) morse ID for a given tuned VOR frequency?

I would assume that when the FMS is set up to autotune enroute VORs for VOR/VOR or VOR/DME updating of the IRU/GPS position, that it would, of necessity, not make use of any VOR which has a missing identifier - i.e., no morse code sent within the specified time window. Likewise, how would the FMS treat an ILS localizer with a missing identifier in a CAT II or CAT III approach? Obviously if no signal is being received, or if the signal strength is below a certain threshold, the localizer needle will not appear - but what happens when the signal is suffcient, but the ID is missing? Does the FMS take that into account in allowing or disallowing a full or partial autoland?

Jim Barrett

[John H Watson]

Does the 747 FMS have the logic to deal with a missing (as opposed to incorrect) morse ID for a given tuned VOR frequency?

The FMC doesn't do any audio decoding/detecting. Only the receivers do that for display purposes. The FMC should, however, command the nav radios to scan for functioning navigation stations. They may be putting out false information, but this should be rejected by the FMC if the computations don't make any sense (e.g. one groundstation telling the FMC it is flying West, but another groundstation telling it that it is flying East).

[Hardy Heinlin]

In Sydney, Australia, entering "MGM", a VOR in the USA (with the freq 112.10), on the Nav Rad page, the CDU will always show MGM, but the ND will decode and show SY (a local Sydney VOR with the same frequency)

Is that what we are trying to confirm?

Yes, thanks!

I'll bloat my code accordingly ...

(6 more bytes for the network and situation management.)


Cheers,

|-|ardy

[Michel Vandaele]

I have addional information concerning the VOR /NDB selection.
According to my source in a big cargo airliner, when selecting a VOR in the LSK1L or 1R, a page is coming up with all possiblities for that 3 letter code with the coordinates.  Pilot then has to make proper selection based on the nearest coordinations.
This can of course be very recent software.
B. Rgds
Michel

[John H Watson]

Does anyone have an example of a VOR or NDB with an identical name?

[Hardy Heinlin]

TGO

(Two VORs)


(NDB identfiers in the FMC?)

[Michel Vandaele]

As far I know, for NDB's you can't use the indentfiers code. Only a freq.
B. Rgds
Michel

[Hardy Heinlin]

I have modified my code. The pilot entered VOR identifier now remains displayed on the NAV RAD page even if a different station is received with the associated frequency.

This means, if you have entered "TGO" and fly across Europe with 112.50 tuned, the ND will change the VOR identifier about every 100 miles -- while the NAV RAD page keeps showing "TGO".

This effect has to be accepted. If it were inhibited, the whole logic of a station-independent NAV RAD identifier entry would not work.


Cheers,

|-|ardy

[Holger Wende]

As far I know, for NDB's you can't use the indentfiers code. Only a freq.

Hi Michel,

This surprised me, therefore I re-read the related pages in Bill Bulfers "Big Boeing FMC User's Guide" (edition Jan 99): He wrote regarding NAV RAD:

...You could tune any VOR, ILS or NDB through the NAV RAD page, using either frequency or the 3 or 4 letter identifier...

Therefore I thought that NDB identifiers could be used as well. But this seems to be only half of the truth because 2 pages later he wrote regarding ADF:

Valid entries are ADF frequencies consisting of a 3 or 4 digit number, optionally, followed by a decimal point and a tenth digit.

While reading I found the following particularly interesting:

Navaid Identifies Decoding
The morse code identifier of a tuned VOR, ILS, DME or ADF can be converted to alpha characters. The decoded identifier is then shown on the PDF and ND
...
Then identifier name is not compared with the FMC...

So the same logic discussed/implemented for VORs seems to be applicable for the other nav types as well?

Regards, Holger

[Hardy Heinlin]

Hi Holger,

the 744 FMS database has no NDB identifiers in store. Edit: I mean NDB frequencies. Hence it cannot assign NDB freqs to NDB IDs.

I wonder why he wrote "you could". Is that past tense and taken out of context of another text? Or is it a hypothetical "could"?

The PFD shows ILS, ILSDME and markers only. No VOR or ADF. The ID decoding is actual Morse tone decoding, it's not an ID taken from the FMS database.


Cheers,

|-|ardy