1.3.1  Means of transmission
1.3.1.1 Except as provided in 1.3.2.1, information shall be disseminated to aircraft by one or more of the following means as determined by the appropriate ATS authority:
PANS-RAC (Doc 4444)
a)  the preferred method of directed transmission on the initiative of the appropriate ATS unit to an aircraft, ensuring that receipt is acknowledged; or
b)  a general call, unacknowledged transmission to all aircraft concerned; or
c)  broadcast; or
d)  data link.

Note.— It should be recognized that in certain circumstances, e.g. during the last stages of a final approach, it may be impracticable for aircraft to acknowledge directed transmissions.
1.3.1.2 The use of general calls shall be limited to cases where it is necessary to disseminate essential information to several aircraft without delay, e.g. the sudden occurrence of hazards, a change of the runway-in-use, or the failure of a key approach and landing aid.
1.3.2  Transmission of special air-reports,
SIGMET and AIRMET information

1.3.2.1 Appropriate SIGMET and AIRMET infor-mation, as well as special air-reports which have not been used for the preparation of a SIGMET, shall be disseminated to aircraft by one or more of the means specified in 1.3.1.1 above as determined on the basis of regional air navigation agreements.
1.3.2.2 The special air-report, SIGMET and AIRMET information to be passed to aircraft on ground initiative should cover a portion of the route up to one hour’s flying time ahead of the aircraft except when another period has been determined on the basis of regional air navigation agreements.
1.3.3  Transmission of information
concerning volcanic activity

1.3.3.1 Information concerning pre-eruption volcanic activity, volcanic eruptions and volcanic ash clouds shall be disseminated to aircraft by one or more of the means specified in 1.3.1.1 above as determined on the basis of regional air navigation agreements.
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1.3.4  Transmission of information concerning radio-active materials and toxic chemical “clouds”
1.3.4.1 Information on the release into the atmosphere of radioactive materials or toxic chemicals which could affect airspace within the area of responsibility of the ATS unit shall be transmitted to aircraft by one or more of the means specified in 1.3.1.1 above.
1.3.5  Transmission of selected special reports and amended aerodrome forecasts
1.3.5.1 Selected special reports and amended aerodrome forecasts shall be transmitted on request and supplemented by:
a)  directed transmission from the appropriate air traffic services unit of selected special reports and amended aerodrome forecasts for the departure, destination and its alternate aerodromes, as listed in the flight plan; or
b)  a general call on appropriate frequencies for the unacknowledged transmission to affected aircraft of selected special reports and amended aerodrome forecasts; or
c)  continuous or frequent broadcast of current aerodrome reports and forecasts in areas determined on the basis of regional air navigation agreements where traffic congestion dictates.

1.3.5.2 The passing of amended aerodrome forecasts to aircraft on the initiative of the appropriate air traffic services unit should be limited to that portion of the flight where the aircraft is within a specified time from the aerodrome of destination, such time being established on the basis of regional air navigation agreements.
1.3.6  Transmission of information on heavy or medium unmanned free balloons
1.3.6.1 Appropriate information on heavy or medium unmanned free balloons shall be disseminated to aircraft by one or more of the means specified in 1.3.1.1 above.
1.3.7  Transmission of information to supersonic aircraft
1.3.7.1 The following information shall be available at appropriate area control centres or flight information centres for aerodromes determined on the basis of regional air navi-
　
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