ICAO Doc 4444
4.12 REPORTING OF OPERATIONAL AND METEOROLOGICAL INFORMATION
184.108.40.206 When operational and/or routine meteorological information is to be reported, using data link, by an aircraft en route at times where position reports are required in accordance with 220.127.116.11 and 18.104.22.168, the position report shall be given in accordance with 22.214.171.124 (requirements concerning transmission of meteorological information from ADS-C equipped aircraft), or in the form of a routine air-report. Special aircraft observations shall be reported as special air-reports. All air-reports shall be reported as soon as is practicable.
4.12.3 Contents of special air-reports
126.96.36.199 Special air-reports shall be made by all aircraft whenever the following conditions are encountered or observed:
b) moderate or severe icing; or
c) severe mountain wave; or
d) thunderstorms, without hail that are obscured, embedded, widespread or in squall lines; or
e) thunderstorms, with hail that are obscured, embedded, widespread or in squall lines; or
f) heavy duststorm or heavy sandstorm; or
g) volcanic ash cloud; or
h) pre-eruption volcanic activity or a volcanic eruption.
Note.— Pre-eruption volcanic activity in this context means unusual and/or increasing volcanic activity which could presage a volcanic eruption.
i) moderate turbulence; or
j) hail; or
k) cumulonimbus clouds.
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