SquawkBox

[Merritt Kinon]

Hi All,

I am unclear about how to set-up SELCAL for my a/c. Is the SELCAL code a numeric number like a squawk code or is it similar to a callsign? Any info and a sample example would be greatly appreciated.

Merritt

ps - SB3 is great! Well worth the wait

[George S. Marinakis]

SELCAL is neither a numeric code nor a callsign. It is a type of ground-to-air communication system developed for use with HF (High Frequency, a.k.a "shortwave"). On long, oceanic flights, standard VHF communication is not usable. The reason for this is that VHF is line of sight. As a station (such as an aircraft) moves over the horizon, it can no longer receive the VHF signal. Since shortwave signals are not affected by this limitation (since the atmosphere reflects them back to the ground), it is more suitable for long range communications.

If you have ever listened to shortwave radio (other than a broadcast station), there is constant static in the background. This is annoying and difficult for pilots to listen to for hours and hours. So SELCAL was developed as a tool for alerting the flight deck of when ATC was trying to contact them. SELCAL consists of both an aural and a visual alert and allows the flight crew to not have to constantly monitor the HF frequency.

The SELCAL system consists of a ground-based SELCAL encoder and a VHF or HF communication system and the airborne decoder. Each aircraft's "SELCAL decoder" is assigned a unique code. The airborne SELCAL decoder is connected to the aircraft's VHF and HF radios. When the aircraft is called, an aural alert is received and the active radio is identified on the cockpit annunciator panel, signaling the flight crew to contact ATC on the active radio frequency.

The SELCAL itself is made up of two pair tones. The individual tone frequencies are designated by the letters A - S (excluding "I" and "O"). For example, a typical aircraft selcal code would be "AB-JM" where "AB" is the first tone pair and "JM" is the second. The tone, when generated on the ground by ATC will cause the SELCAL decoder on the flight deck of the particular aircraft to sound an aural and visual cue, alerting the crew to contact ATC (this has use not only for ATC but also for company communications. The flight crew can monitor a separate HF frequency which is a company frequency. If dispatch or someone else needs to contact an aircraft, they can hop onto the company freq. and use SELCAL to get the flight crew's attention).

If you want to hear what the codes sound like, navigate to the folder where SB3 was installed and go to the /sound/selcal folder. There you will see all of the tone pairs. Click on the <ab.wav> file and then about one second later, click on the <jm.wav> file. The sounds you here are exactly what a SELCAL sounds like in the real world.

SELCALs are assigned to airlines by ARINC (Aeronautical Radio, Inc.) There are a total of 10,920 available codes so there is obviously some duplication. ARINC gets by this problem by issuing duplicate codes to aircraft operating in the different parts of the world so in theory, they will never be working in the same area on the same frequency with the aircraft they share their code with.

There is a section in the SB3 manual that explains exactly how to set up your SELCAL. ATC will see your code in the remarks section of your flightplan on ASRC.

Hope this helps.

[Merritt Kinon]

Hi George,

Thanks for the great reply!

Sincerely,
merritt

[somejeff]

Now that's the most facinating post I've read here so far... (other than Joel's responses, we must ALL read those....)

[hans]

And,

I can also recommend VATSIM-UK's Oceanic pages, as well as the same under Eurocenter VACC (EUC VACC), where this is also explained.

Regards,