Conditions to start an instrument approach?

[Adam S]

What conditions must be met in order to be able to start an instrument approach?
Cloud base? Vis? RVR?

Thank you

[Jolax]

An instrument approach may be commenced regardless of the reported RVR/visibility.
if the reported RVR/visibility is less than the applicable minimum, the approach shall not be continued:
-below 1000ft AGL
-into the final segment if the DA/MDA (H) is more than 1000ft AGL.

[uncle dickie]

And perhaps stating the obvious, ATC approval for the procedural approach as well.
From a practical point of view, unless there is reasonable expectation of a successful approach you wait until the RVR is at or above your minima, otherwise you are wasting fuel.

[Adam S]

Thank you!