Wake up, little Boeing, wake up – ICAO Selcal · 4 | HF is in the Air – A Primer on Aero Bands Wake up, little Boeing, wake up – ICAO Selcal | 5 ©2016, Nils Schiffhauer, DK8OK

4 | HF is in the Air – A Primer on Aero Bands Wake up, little Boeing, wake up – ICAO Selcal | 5

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2016, Nils Schiffhauer, D

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Wake up, little Boeing, wake up – ICAO Selcal

Since 1957, each airplane is identified by a code of 2 x 2 letters, e.g. QS-HM. This is the “selective callsign”, or Selcal. Each of the 16 used letters is coded by one specific of 16 tones from 312,6 Hz to 1.479,1 Hz. The tones are transmitted in two groups of one second length each, separated by a gap of 200 milliseconds, e.g.; 1.203,3 Hz/1.497,1 Hz (= QS) and 654,7 Hz/977,2 Hz (= HM), see top.

The aircraft has to submit its Selcal to all ground stations en route, e.g. by its Flight Plan, or during a VHF contact. At least in the initial HF contact, the ground station is transmitting the Selcal to check if it works, and the airplane can be reached by this one during flight. The Selcal is generally transmitted in USB with full carrier. See the video at the bottom of this page for a live example.

Many decoders do offer decoding ICAO Selcals, among them Sorcerer and MultiPSK. Nevertheless, decoding can be a bit tricky for at least four reasons:• Speech formants are interpreted as tones. Remedy: Take care to

check the decoder only when there is no speech.• Noise is interpreted as tone. Remedy: Reduce the audio level

that there is (nearly) no output under noise.• Even slight deviations of the frequency of your receiver may pro-

duce other tones, and so an incorrect Selcal. Remedy: Switch to AM, which offers the most precise method.

• Transmitter is over-modulated, producing many and strong har-monics. Remedy: Try to sort out the 2 x 2 strongest frequencies manually. A table of frequencies/letters is part of the Selcal Us-er’s guid, see below.

Airframes.org provides a lookup for e.g. ICAO Selcals. You will soon realize that most Selcals are given out to multiple airplanes. So you often need some additional information in assigning the decoded

Figure 1: There are many Selcal decoders around, but MultiPSK delivers one of the best performances. Here you see the 2 x 2 tones of N829MH, a Boe-ing 767-432 of Delta Airlines on a flight from John F. Kennedy International to Nice Cote d’Azur, Flight Number DAL412, called by Gander on 5.616 kHz at 03:05 UTC on June 9th, 2016.

Figure 2: How Selcal generally works: ground Station is transmitting the the Selcal, and Aircraft Station is receiving it. There it is decoded in the Airborne Selective Calling Unit, If matching the aircraft’s Selcal, this call is indicated by light or a buzzer (“Indicator”). From ASRI’s User’s Guide.

Video 1: This video (click onto the still picture above to get it running) shows the normal procedure: Gander is asking Flight Number DAL412 (see also Figure 1) for its Selcal via voice. DAL412 is giving it as “QS-HM”. Then Gander is transmitting the Selcal, and DAL412 eventually acknowledges it.

Selcal to the correct airplane, e.g. the Flight Number. You will not find many Selcals of military airplanes, as these information is not available for the public. Some additional background information on Selcals and their applications is found in the User’s Guide of Avia-ton Spectrum Resources, Inc. ASRI, which officially issues Selcals.

Figure 3: After having decoded the Selcal, you may look it up at the “Aircraft Registration Data-base” of Airframes.org. Here we have luck that under “QS-HM” we find (a) just one (b) entry.

Figure 4: Next step maybe to look up the Flight Number (DAL412) at e.g. FlightAware. There you get a lot of more information, neatly visualized.

Figure 5: You may also have a look onto the “logbook” of FlightAware in a list format. I marked that entry yellow, where I received the Selcal.

Figure 6: Selcals are not always as clear as shown above. Here Santa Maria is transmitting Selcal DM-EJ with audio frequencies 426,6 Hz/977,2 Hz and 473,2 Hz/716,1 Hz. Due to too many harmonics, this Gulf Stream 6 of GainJet Aviation, a private jet charter, answered “Negative Selcal” on Flight Number GNJ65. HF sonagram, to ensure that harmonics are real and not being introduced during demodulation. The correct fundamentals had been marked within this paling.

http://www.kd0cq.com/2013/07/sorcerer-decoder-download/http://f6cte.free.fr/index_anglais.htmhttp://www.airframes.orghttps://www.asri.aero/wp-content/uploads/2012/07/110914-ASRI-SELCAL-Users-Guide-61742-Rev-C.pdfhttps://www.asri.aero/wp-content/uploads/2012/07/110914-ASRI-SELCAL-Users-Guide-61742-Rev-C.pdfhttp://flightaware.com

6 | HF is in the Air – A Primer on Aero Bands Wake up, little Boeing, wake up – ICAO Selcal | 7

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16, N

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Figure 7: After Ground Station and airplane have exchanged Selcal, the Ground Station can call & alert the pilot. Here Gander first calls REACH 191 in voice. With no answer on this way, Gander sends out its Selcal KM-AG three times. After that, REACH 191 answers in voice, and Gander can give through a change of level clearance. Click onto the loudspeaker icon on the right to listen to this communications. As REACH 191 is a plane of the US Air Force, no further information is available for the public – no solution of the Selcal, no trace at FlightAware. You have to fully rely on monitoring HF!

Figure 8: Rarely, also full AM (i.e. both sidebands with carrier) are also found with legacy equipment. See this example of LDOC Nairobi on 13.330 kHz. This shouldn’t be mixed up with signal having just a bad suppression of the lower sideband … Even more rarely, you may find a pure LSB Selcal with car-rier (e.g. with Stockholm Radio).

Selcal Tone [Hz] Designation plus from September, 2016 312,6 A 329,2 T 346,7 B 365,2 U 384,6 C 405,0 V 426,6 D 449,3 W 473,2 E 498,3 X 524,8 F 552,7 Y 582,1 G 613,1 Z 645,7 H 680,0 1 716,1 J 754,2 2 794,3 K 836,6 3 881,0 L 927,9 4 977,2 M 1.029,2 5 1.083,9 P 1.141,6 6 1.202,3 Q 1.266,2 7 1.333,5 R 1.404,4 8 1.479,1 S 1.557,8 9

Figure 9: List of the 16 Selcal tones and their desig-nations, see the two first columns. 2013 it has been recommended by ICAO/ASRI to double this pool from September, 2016 – see the last two columns. Even if this recommendation will materialize from that day or later, the “old” Selcal tones will work furthermore.