Mode-S Flight ID question

[mighty3507]

Hello all,

    I have been reading this board for a while now.  I finally bit the bullet and purchased a Radar Box. It arrived yesterday and I have been learning and enjoying. I am using the supplied antenna in the attic in our two story house.  I might get the antenna outside at some point, but I am pleased with the range so far.

    I did have a question. Most of the traffic in the area is Mode-S. While the ADS-B flights have their ID’s and routes displayed, I have yet to see a Mode-S flight have a complete flight ID translation. JetBlue is the only airline I have seen that has at least the flight number displayed ‘37’ or ‘353’ etc. I understand if the crew does not input the flight ID it will not be displayed. However, it seems strange that not one airline inputs the value. So, is this the just the way it is in the U.S. or is it something else? I did attach a screen shot showing what I see in the ‘MyFlights’ listing.

    I did find this thread on a Mode-S flight ID issue, but I do not know if is related.
http://www.airnavsystems.com/forum/index.php?topic=1372.0
Thanks,

--Steve in Southern California


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[tarbat]

V2.10 will fix this, and you'll see FlightIDs on most (maybe not all) ModeS aircraft.

[DaveReid]

V2.10 will fix this, and you'll see FlightIDs on most (maybe not all) ModeS aircraft.

Specifically those which send FlightID as an ELS parameter, which RadarBox currently ignores - it only decodes FlightIDs sent via the ADS-B Identification squitter.

[tarbat]

Even more specifically, FlightIDs sent in the extended data found in DF20 (Altitude) and DF21 (Squawk) downlink messages.

Example screenshot:

[DaveReid]

Even more specifically, FlightIDs sent in the extended data found in DF20 (Altitude) and DF21 (Squawk) downlink messages.

Indeed so - DF20 and DF21 are the only downlink formats that contain the ELS/EHS parameters.

[tarbat]

Indeed so - DF20 and DF21 are the only downlink formats that contain the ELS/EHS parameters.

That's what testing indicates.  DF20/DF21 messages can also contain other data, so RB v2.10 also has to determine whether the data in DF20/DF21 messages actually contain a FlightID and not other data.

This was tested by comparing a days log from RBv2.10 vs. a days log from Planeplotter.  There was a close match between aircraft showing FlightID in PP vs. RBv2.10, with just a few discrepancies, likely caused by different reception conditions.

Dave, confirm something for me.  Are DF20/DF21 messages only transmitted in response to a ground station, or are they transmitted all the time?

[malc41]

Tarbat

I'm sure that Dave will confirm but my understanding is that DF20/DF21 are only transmitted in response to the UF20/UF21.

UF20 being a request for altitude
UF21 being a rewuest for airframe ID

[tarbat]

Thanks malc41.  Thats also what I suspect, and might explain why sometimes I saw FlightIDs in Planeplotter that didn't appear in RB2.10, and other times they appeared in RB2.10 and not in PP.

Probably depends whether there's an active ModeS radarhead in the locality of the sharer on PP.

[malc41]

Tarbat

Yes its a tricky subject to get the head around. Waiting with fingers crossed for v2.1 and then hopefully the problem will be solved.

[dudbaker]

Hi

Remember, requests for data can come from TCAS equipped aircraft as well radar head.

Dudley

[DaveReid]

I'm sure that Dave will confirm but my understanding is that DF20/DF21 are only transmitted in response to the UF20/UF21.

UF20 being a request for altitude
UF21 being a request for airframe ID

Yes - UF20 and UF21 are the extended versions of the standard UF4/UF5 uplinks, which request altitude and squawk respectively.

The difference is that the UF20/UF21 also contains a request for the contents of one of the transponder registers, which are sent in the DF20/DF21 response.

The registers normally requested are:

for ELS:

BDS1,0: Data Link Capability report
BDS2,0: Aircraft Identification (i.e. Flight ID)
BDS3,0: Active TCAS RA(s)

and, for EHS:

BDS4,0: Selected Vertical Intention
BDS5,0: Track and Turn report
BDS6,0: Heading and Speed report

[malc41]

Dave

Where would we be without you ;-)

[Brisbane]

On the same tack, is that why Delta never show flight i.d. The only one's that seem to tie-up are the 767-400's.

[DaveReid]

On the same tack, is that why Delta never show flight i.d. The only one's that seem to tie-up are the 767-400's.

Same reason as above:  no ADS-B squitter = no Flight ID (currently) displayed by RB. 

The DAL B764s are AFAIK the only ones in their fleet that do have ADS-B, that's why you see their Flight IDs.

[WAL 2T]

Another tech question for Dave: I understand from above that the flight id data held in the DF20/21 frames is not currently parsed by the RB software, what about the Mode S only flights which do display a flight id in the current version of the software? are these differences due to different models of transponder? or does this indicate that they have different capabilities?

cheers