Selcal Selective Calling Chapter 7 Selcal Selective Calling

SELCAL system The SELCAL system operates through the aircraft com radios and VHF). Each aircraft has a code that SELects that particular aircraft to be CALled, however since there are only 10,000 possible codes, some codes are being assigned to more than one aircraft. To deal with the problem of code shortage, every attempt is made to assign the same code to aircraft on opposite sides of the world. On HF, different HF channels are assigned to aircraft using the same code. SELCAL will eventually be provided through Satcom.

SELCAL Ground Network SELCAL messages are sent through an ARINC control station (in the US). ARINC relays the message to the airline company, usually through phone lines. SELCAL overwater uses HF instead of VHF.

SELCAL Control Panel Light Light Reset Button Here is the SELCAL controller located in the flight deck. When being called, a chime will sound and a light will light, letting the crew know they are being paged. The crew will then turn up the volume on their com radio (either HF or VHF) so they can respond to the call. Pressing the RESET button arms the system for the next call.

SELCAL Decoder Textbook page 46 In the E&E bay, is a SELCAL decoder, the “black box” for the SELCAL system. A 4-letter code is assigned each aircraft (excluding the letters I, N and O), which is entered on the face of the SELCAL decoder, by thumbwheels. Some aircraft have 2 decoders: One for HF and one for VHF, for up to 4 radios (2 for each band).

SELCAL Block Diagram Textbook page 48

How a SELCAL Code is Generated Textbook page 47 Code consists of 4 tones from the 16 audio frequencies shown on the left. They are sent in 2 pairs: “A” & “B” are mixed together (312.6 & 346.7 HZ) and transmitted for 1 second. Then, after a .2 second interval, “C” & “D” (384.6 & 426.6 HZ), is transmitted for 1 second.

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Review Q&A Chapter 7 SELCAL 7.1 What does the contraction “SELCAL” mean? Answer: Selective Calling. 7.2 Give 2 reasons why SELCAL is used. Answer: Reduce crew workload and extend the range of VHF. 7.3 How many tones are in a SELCAL code? Answer: 4 7.4 How many SELCAL tone pairs are transmitted simultaneously? Answer: 2 7.5 Can 2 aircraft have the same SELCAL code? Answer: Yes 7.6 What precaution is necessary if a pilot receives a SELCAL intended for a different airplane? Answer: He must clearly identify his flight to the ground station. 7.7 How is the problem reduced where 2 aircraft have the same SELCAL code? Answer: Either by assigning the same code to aircraft on opposite sides of the globe or by assigning different HF channels (HF only). 7.8 How is the pilot warned of an incoming SELCAL message? Answer: By a light illuminating on the SELCAL control panel and a chime.