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Do CAVOK (ceiling and visibility okay) and CAVU (ceiling and visibility unlimited) have formal definitions worldwide?

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CAVOK, source: formercaptain.ca

Are they used in ATC communications?

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CAVOK is formally defined in ICAO Annex 3 ( APP3-2 2.2 Use of CAVOK ) . You can hear it at the airports where there is no ATIS , when ATC communicates the weather info. CAVU is not formally defined in Annex 3 .

When the following conditions occur simultaneously at the time of observation:

 a) visibility, 10 km or more, and the lowest visibility is not reported;
 b) no cloud of operational significance;
 c) no weather of significance to aviation as given in 4.4.2.3 and 4.4.2.6;

information on visibility, runway visual range, present weather and cloud amount, cloud type and height of cloud base shall be replaced in all meteorological reports by the term “CAVOK”.

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  • $\begingroup$ Could you quote the actual definition from the document you refer to? $\endgroup$ – Jan Hudec Mar 4 '16 at 10:05
  • $\begingroup$ So what may be the difference between CAVOK and CAVU? $\endgroup$ – lemonincider Sep 18 '17 at 6:00
  • $\begingroup$ This answers 1/2 of the question (while CAVU isn't defined by ICAO, it still has a meaning...) $\endgroup$ – Lnafziger Sep 20 '17 at 15:50
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CAVU means: "CLEAR OR SCATTERED CLOUDS AND VISIBILIY UNLIMITED (GREATER THAN TEN MILES)"

CAVOK means: "CLOUD AND VISIBILITY OK (METAR)."

This military document, has a little more background:

Overseas locations may use the contraction “CAVOK” (ceiling and visibility OK). CAVOK is used when there is no significant weather, the visibility is 10 km or greater, and the ceilings are greater than 5,000 ft.

I have never heard them used in verbal ATC communication, and they are not listed in the Pilot/Controller Glossary so should not be used on the radio.

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Actual Definition From Annex 3 When the following conditions occur simultaneously at the time of observation: a) visibility, 10 km or more, and the lowest visibility is not reported;

Note 1.— In local routine and special reports, visibility refers to the value(s) to be reported in accordance with 4.2.4.2 and 4.2.4.3; in METAR and SPECI, visibility refers to the value(s) to be reported in accordance with 4.2.4.4. Note 2.— The lowest visibility is reported in accordance with 4.2.4.4 a).

b) no cloud of operational significance; c) no weather of significance to aviation as given in 4.4.2.3, 4.4.2.5 and 4.4.2.6; information on visibility, runway visual range, present weather and cloud amount, cloud type and height of cloud base shall be replaced in all meteorological reports by the term “CAVOK”.

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