8.3 Communication with Aircraft

CALLSIGN CONFUSION

8.3.1 Controllers should be aware that the similarity of some aircraft call signs can cause confusion which could lead to incidents. In many cases strict R/T discipline can alleviate the problem. Call signs which contain three or more common digits are particularly liable to be confused. When there is a likelihood that call signs will be confused, the pilots of the aircraft concerned should be warned, especially when the flight number are identical, e.g. SAA515 and SFR515.

8.3.2 Callsign abbreviation must not be used when two aircraft on the same frequency have similar registrations e.g. ZS-SSB and VP-SSB. In this situation both aircraft are to be instructed to use full callsign.

8.3.3 The omission of the company designator when it is an integral part of a callsign can lead to confusion with other numerical and literal information, e.g. levels, headings, reporting point designations, etc. It may also negate the ‘alerting’ effect on the pilot of hearing his own company designator. Therefore, company designators must always be used when they are part of a callsign.

ESTABLISHMENT OF CONTACT

8.3.4 The initial call made to establish RTF contact should take the following form:-

a) The full RTF callsign of the station being called;

b) The full RTF callsign of the station calling, e.g. ‘Springbok 302 – Cape Town Tower.

8.3.5 The phrase ‘continue as cleared’ should not be used when replying to an initial call made by an aircraft which has been transferred from another frequency.

READABILITY OF TRANSMISSION

8.3.6 When the checks are made the following readability scale is to be used to indicate the quality of the transmission.

Quality

Scale

UNREADABLE

READABLE NOW AND THEN

READABLE BUT WITH DIFFICULTY

READABLE

PERFECTLY READABLE

ACKNOWLEDGE AND READ BACK OF MESSAGES

8.3.7 As a general principle, all messages should be acknowledged by the use of the aircraft callsign.

8.3.8 Executive instructions will be acknowledged by an abbreviated read back of the instructions, e.g.:-

a) ZS-BCD aircraft landing runway 03, hold position. Reply ‘BCD holding’

8.3.9 A full read back will be made to messages containing any of the following:-

a) level Instructions.

b) Heading Instructions.

c) Speed Instructions.

d) Airways or route clearances.

e) Runway-in-use.

f) Clearance to enter, land on, take-off on, backtrack or cross an active runway.

g) SSR operating instructions.

h) Altimeter settings.

i) VDF information.

j) Frequency changes.

k) The controller shall listen to the read-back to ascertain that the clearance or instruction has been correctly acknowledged by the flight crew, and shall take immediate action to correct any discrepancies revealed by the read-back.

TRANSFER OF COMMUNICATIONS

8.3.10 To transfer communication with an aircraft to another unit, controllers shall pass instructions giving:-

a) The identity of the unit to be contacted;

b) The frequency to be used for contact.

8.3.11 When the frequency of an aeronautical mobile service station is an intermediate 25 kHz the full figure will comprise 6 digits. However, controllers transferring aircraft to these frequencies are to use only the first 4 digits, e.g.:-

FREQUENCY	SPOKEN	PRONUNCIATION
124.700	124.7	WUN TOO FOWER DAY-SEE-MAL SEVEN
120.050	120.050	WUN TOO ZERO DAY-SEE-MAL ZERO FIFE ZERO
119,775	119,775	WUN WUN NINER DAY-SEE-MAL SEVEN SEVEN FIFE

8.3.12 If no further communication is received after acknowledgement, satisfactory transfer of communication may be assumed.

LOSS OF COMMUNICATION

8.3.13 Refer to Section 2 GENERAL – CHAPTER 10 RADIO FAILURE PROCEDURES

EMERGENCY COMMUNICATION

8.3.14 Distress and urgency traffic shall comprise all radio-telephone messages relative to the distress and urgency conditions respectively. Distress and urgency conditions are defined as:-

a) Distress: a condition of being threatened by serious and/or imminent danger and of requiring immediate assistance.

b) Urgency: a condition concerning the safety of an aircraft other vehicle, or of some person on board or within sight, but which does not require immediate assistance.

8.3.19 The radiotelephony distress signal MAYDAY and the radiotelephony urgency signal PAN shall be used at the commencement of the first distress and urgency communication respectively. If time permits the signal MAYDAY or PAN should be repeated 3 times in the initial call.

8.3.20 In distress and urgency traffic the radiotelephony distress and urgency signals should be used at the commencement of any subsequent communications so as to indicate to any station which may have just joined the frequency that there is distress or urgency traffic in progress with which they must not interfere.

8.3.21 Distress and urgency traffic will normally be maintained on the frequency on which such traffic was initiated until it is considered that better assistance can be provided by transferring that traffic to another frequency.

8.3.22 In case of distress and urgency communications, in general, the transmissions by radiotelephone should be made slowly and distinctly, each word being clearly pronounced to facilitate transcription.

DISTRESS COMMUNICATIONS

8.3.23 The distress call and message should preferably be sent on the air-ground frequency in use at the time.

8.3.24 The distress call and message shall be preceded by the distress signal “Mayday”, preferably spoken three times if time permits.

8.3.25 The distress call may be addressed to a specific aeronautical ground station, normally that station communicating with the aircraft or in whose area of responsibility the aircraft was operating; or it may be broadcast without being addressed to any station.

8.3.26 Whenever possible the distress message should be transmitted in the same transmission as the distress call.

8.3.27 The foregoing provisions are not intended to prevent:-

a) The distress message of an aircraft being made on another aeronautical mobile frequency, if considered necessary or desirable;

b) The distress message of an aircraft being broadcast, if time and circumstances make this course preferable;

c) The aircraft transmitting on the maritime mobile service radiotelephone calling frequencies;

d) The aircraft using any means at its disposal to attract attention and make known its condition;

e) Any station taking any means at its disposal to assist an aircraft in distress.

Note: The station addressed will normally be that station communicating with the aircraft or in whose area of responsibility the aircraft is operating.

ACTION BY GROUND STATION ADDRESSED

8.3.28 The station addressed by an aircraft in distress or first station to acknowledge the distress message shall:-

a) Immediately acknowledge the distress message;

b) Take control of the communications, or specifically and clearly transfer that responsibility, advising the aircraft if a transfer is made;

c) Take immediate action to ensure that all necessary information is made available, as soon as possible to the appropriate ATSU.

d) Warn other stations, as appropriate, in order to prevent the transfer of traffic to the frequency of the distress communication.

IMPOSITION OF SILENCE

8.3.29 The station in distress, or the station in control of distress traffic, shall be permitted to impose silence, either on all stations of the mobile service in the area or on any station which interferes with the distress traffic. It shall address these instructions “to all stations”, or to one station only, according to circumstances.

8.3.30 When a ground station imposes silence on a frequency it may transfer aircraft, other than the aircraft in distress, to another frequency in which case the frequency must be stipulated.

ACTIONS BY OTHER STATIONS

8.3.31 The distress communications have absolute priority over all other communications and a station aware of them shall not transmit on the frequency concerned, unless:-

a) The distress is cancelled or the distress traffic is terminated;

b) All distress traffic has been transferred to other frequencies;

c) The station controlling communications gives permission:

d) It has itself to render assistance.

8.3.32 Any station which has knowledge of distress traffic and which cannot itself assist the station in distress shall nevertheless continue listening to such traffic until it is evident that assistance is being provided.

URGENCY COMMUNICATIONS

8.3.33 The urgency call and message should preferably be sent on the air-ground frequency in use at the time.

8.3.34 The urgency call and message should be preceded by the urgency signal “Pan”, preferably spoken three times.

8.3.35 The urgency call should normally be addressed to a specific station.

8.3.36 Whenever possible the urgency message should be transmitted in the same transmission as the urgency call.

ACTION BY GROUND STATION ADDRESSED

8.3.37 The station addressed by an aircraft reporting an urgency condition, or first station acknowledging the urgency message, shall:-

a) Acknowledge the urgency message;

b) Take immediate action to ensure that all necessary information is made available, as soon as possible to:-

i) The appropriate air traffic services unit;

ii) The aircraft operating agency concerned.

Note: The requirement to inform the aircraft operating agency does not have priority over any other action which involves the safety of the aircraft or any other aircraft in the area or which might affect the progress of expected flights in the area.

c) If necessary, exercise control of communications.

PRIORITY OF URGENCY COMMUNICATIONS

8.3.38 The urgency communications have priority over all other communications, except distress, and all stations shall take care not to interfere with the transmission of urgency traffic.