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Feedback re incorrect SELCAL Code parameters


Allan Dawson
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Greetings guys,

I wasn't sure where to post this as although I've noticed this issue when using the xPilot app, I suspect it actually applies to the network as a whole, so I thought "General" might be more appropriate than in the xPilot section.

The issue I noticed is that there is an error within the parameters for allowable SELCAL codes on xPilot and the reason I suspect this applies everywhere is because the same error appears in the way the limitations are described on Wikipedia and also within some ICAO documents, so it's not surprising this error will have been copied down to VATSIM.

The apparent "rule" states that you cannot have the same letter repeated within a SELCAL code, but this is actually not quite correct. Presumably this is because whoever wrote the original guidance either missed a point through translation, or simply forgot to proof-read that it was described correctly - we're all human! The correct restriction is that you cannot have repeated letters within a block pair, but the same letter can appear twice between the two pairs.

For example: AA-BB or BB-DD are not valid.

However: AB-BC and AB-BS are examples of actual valid SELCAL codes in use on real aircraft I have had dealings with, but these codes are rejected by xPilot on behalf of the network.

(I included the dashes here to emphasise the pairs i.a.w convention, but obviously I understand the dashes should not be entered into xPilot)

Obviously this is not a big deal, I just thought I'd offer up the correction in case any dev's are interested, but it's not a showstopper 😀

Current airline pilot on B737 NG/MAX. 
Previously flew B737 300 Non-EFIS & 300/400EFIS

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Hi Allan,

good feedback. Can you please bring some realworld SELCAL examples, please? I had a brief look around some databases and could not find any that would follow your advice. Do you happen to have some tail numbers to look for?

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On 6/16/2021 at 3:22 AM, Allan Dawson said:

However: AB-BC and AB-BS are examples of actual valid SELCAL codes in use on real aircraft I have had dealings with, but these codes are rejected by xPilot on behalf of the network.

xPilot rejects those SELCAL codes because they are invalid. SELCAL codes cannot contain duplicate characters. 

Controller (C3), Los Angeles ARTCC
Developer: xPilot, vATIS

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21 minutes ago, Justin Shannon said:

SELCAL codes cannot contain duplicate characters.

Have you read the bit where OP says that Wikipedia has it wrong?

They didn't provide any sources, but neither did you.

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1 hour ago, Tobias Dammers said:

Have you read the bit where OP says that Wikipedia has it wrong?

They didn't provide any sources, but neither did you.

”SELCAL code assignments have a few rules that are followed to make sure the radio systems are consistent in their usage. Firstly, a character may never be repeated, i.e. a code cannot use the ‘A’ twice. Secondly, the first character of each pair must be shown with the lowest alphanumeric character first, i.e. ‘A’ must be before ‘F’ or ‘D’ must be before ‘3’ or ‘5’ must be before ‘8’.”

https://www.icao.int/SAM/Documents/2019-06901-SAMIG23/SAMIG23_WP12 SELCAL.pdf

https://www.asri.aero/selcal/how-selcal-works/

If the OP can provide actual evidence that these rules are wrong, then I’d be glad to entertain the idea of updating xPilot accordingly. 

Edited by Justin Shannon

Controller (C3), Los Angeles ARTCC
Developer: xPilot, vATIS

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  • 1 month later...
2 hours ago, Denzel de Reuver said:

wait selcals can have numbers?

Not currently. I missed that in the quote I posted; ICAO is proposing an expansion to the usable SELCAL characters, hence the addition of numbers. 

Currently, as far as I’m aware, a SELCAL code can only contain a specific subset of alpha characters. 

Controller (C3), Los Angeles ARTCC
Developer: xPilot, vATIS

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