Special observations are required to be made by all aircraft operating on international air routes whenever the following conditions are encountered or observed: severe or moderate turbulence; severe or moderate icing; severe mountain wave; thunderstorms with or without hail, that are obscured, embedded, widespread or in squall lines; volcanic ash cloud; pre-eruption volcanic activity or volcanic eruption.

Other non-routine aircraft observations are made when other meteorological conditions are encountered (e.g. wind shear) and which, in the opinion of the pilot-in-command, may affect the safety or markedly affect the efficiency of other aircraft operations. These observations are to be made through voice communications by advising the appropriate ATS unit as soon as practicable.

Dissemination of messages:

• national and international exchange (bulletins UAEO60 EETN and UAEO70 EETN)
• publication on Weather Service webpage (lennuilm.ee)

Content of air-reports („uplink“):

1. Message type designator
2. Aircraft identification
3. Condition prompting the issuance of a special air-report

• severe turbulence – SEV TURB [EDRnnn]
• severe icing – SEV ICE
• thunderstorms with hail (obscured in haze; embedded in cloud; widespread or forming a squall line) – TSGR
• thunderstorms without hail (obscured in haze; embedded in cloud; widespread or forming a squall line) – TS
• volcanic ash cloud – VA CLD [FLnnn/nnn] or VA[MT nnnnnnnnnnnnnnn]
• moderate turbulence – MOD TURB [EDRnnn]
  moderate icing – MOD ICE

4. Observed (OBS)
5. Time of occurence in hours and minutes (UTC)
6. Position or latitude and longitude in degrees and minutes
7. Level or range of levels

FLnnn
FLnnn/nnn
nnnnFT

Examples:

UAEO60 EETN YYGGgg
ARS
B735 MOD TURB OBS AT 0820Z N5900E02330 FL300=

UAEO70 EETN YYGGgg
ARS
B735 VA CLD OBS AT 1245Z N5930E02330 FL180/210=