5.2.1.7.3.1 Call Sign Change Restrictions
An aircraft shall not change the type of its radiotelephony call sign during flight, except temporarily on the instruction of an air traffic control unit in the interests of safety.
5.2.1.7.3.1.1 Transmission During Critical Phases
Except for reasons of safety no transmission shall be directed to an aircraft during take-off, during the last part of the final approach or during the landing roll.
5.2.1.7.3.2 Establishing Communications
Full radiotelephony call signs shall always be used when establishing communication. The calling procedure of an aircraft establishing communication shall be in accordance with Table 5-2 (Radiotelephony calling procedure).
5.2.1.7.3.2.2 General Calls
PANS.— Stations having a requirement to transmit information to all stations likely to intercept should preface such transmission by the general call ALL STATIONS, followed by the identification of the calling station.
5.2.1.7.3.2.3 The reply to the above calls shall be in accordance with Table 5-3 (Radiotelephony reply procedure).
5.2.1.7.3.2.4 Uncertain Identification
PANS.— When a station is called but is uncertain of the identification of the calling station, it should reply by transmitting the following:
STATION CALLING . . . (station called) SAY AGAIN YOUR CALL SIGN
(CAIRO station replying)
STATION CALLING CAIRO (pause) SAY AGAIN YOUR CALL SIGN
Commencement of Communication
5.2.1.7.3.2.5 Communications shall commence with a call and a reply when it is desired to establish contact, except that, when it is certain that the station called will receive the call, the calling station may transmit the message, without waiting for a reply from the station called.
5.2.1.7.3.2.6 Interpilot Air-to-Air Communication
Interpilot air-to-air communication shall be established on the air-to-air channel 123.45 MHz by either a directed call to a specific aircraft station or a general call, taking into account conditions pertaining to use of this channel.
5.2.1.7.3.2.6.1 PANS.— As the aircraft may be guarding more than one frequency, the initial call should include the distinctive channel identification “INTERPILOT”.
CLIPPER 123 — SABENA 901 — INTERPILOT — DO YOU READ
or
ANY AIRCRAFT VICINITY OF 30 NORTH 160 EAST — JAPANAIR 401 — INTERPILOT — OVER
5.2.1.7.3.3 Subsequent Communications
5.2.1.7.3.3.1 Abbreviated radiotelephony call signs, as prescribed in 5.2.1.7.2.2, shall be used only after satisfactory communication has been established and provided that no confusion is likely to arise. An aircraft station shall use its abbreviated call sign only after it has been addressed in this manner by the aeronautical station.
5.2.1.7.3.3.2 After contact has been established, continuous two-way communication shall be permitted without further identification or call until termination of the contact.
5.2.1.7.3.3.3 In order to avoid any possible confusion, when issuing ATC clearances and reading back such clearances, controllers and pilots shall always add the call sign of the aircraft to which the clearance applies.
5.2.1.7.3.4 Indicating Transmitting Frequency
5.2.1.7.3.4.1 PANS.— As the aeronautical station operator generally guards more than one frequency, the call should be followed by an indication of the frequency used, unless other suitable means of identifying the frequency are known to exist.
5.2.1.7.3.4.2 HF Frequency Indication
PANS.— When no confusion is likely to arise, only the first two digits of the High Frequency (in kHz) need be used to identify the transmitting channel.
(PAA 325 calling Kingston on 8 871 kHz)
KINGSTON CLIPPER THREE TWO FIVE — ON EIGHT EIGHT
5.2.1.7.3.4.3 VHF 25 kHz Separation
PANS.— Wherever VHF communications channels are separated by 25 kHz, only the first 5 digits should be used to identify the transmitting carrier frequency in radiotelephony communications. Not more than two significant digits after the decimal point are used. In the case of these being two zeros, a single zero is considered significant.
| Channel | Transmitted as |
|---|---|
| 118.000 | ONE ONE EIGHT DECIMAL ZERO |
| 118.005 | ONE ONE EIGHT DECIMAL ZERO ZERO FIVE |
| 118.010 | ONE ONE EIGHT DECIMAL ZERO ONE ZERO |
| 118.025 | ONE ONE EIGHT DECIMAL ZERO TWO FIVE |
| 118.050 | ONE ONE EIGHT DECIMAL ZERO FIVE ZERO |
| 118.100 | ONE ONE EIGHT DECIMAL ONE |
5.2.1.7.3.4.4 VHF Panel Settings
PANS.— In airspace where all VHF voice communications channels are separated by 25 kHz or more and the use of six digits as in 5.2.1.7.3.4.3 is not substantiated by the operational requirement determined by the appropriate authorities, the first five digits of the numerical designator should be used, except in the case of both the fifth and sixth digits being zeros, in which case only the first four digits should be used.
| Channel | Transmitted as | Radio management panel setting for 25 kHz (5 digits) | Radio management panel setting for 8.33/25 kHz (6 digits) |
|---|---|---|---|
| 118.000 | ONE ONE EIGHT DECIMAL ZERO | 118.00 | 118.00 |
| 118.025 | ONE ONE EIGHT DECIMAL ZERO TWO | 18.02 | 18.025 |
| 118.050 | ONE ONE EIGHT DECIMAL ZERO FIVE | 18.05 | 118.050 |
| 118.075 | ONE ONE EIGHT DECIMAL ZERO SEVEN | 118.07 | 118.075 |
| 118.100 | ONE ONE EIGHT DECIMAL ONE | 118.10 | 118.100 |
Chapter 6. VHF Air-Ground Digital Link (VDL)
6.1 Definitions And System Capabilities
The VHF digital link (VDL) is a constituent mobile subnetwork of the aeronautical telecommunication network (ATN), operating in the aeronautical mobile VHF frequency band. In addition, the VDL may provide non-ATN functions, such as, for instance, digitized voice. The very high frequency (VHF) digital link (VDL) Standards and Recommended Practices (SARPs) defined and referenced below apply to aeronautical VHF digital communications systems operating within the aeronautical telecommunication network (ATN).