Originally Posted by
FlightDetent
For reference only, EASA starting point is CAT.OP.MPA.185 Planning minima for IFR flights — aeroplanes. Then it follows to CAT.OP.MPA.110.
If, A conversion from meteorological visibility to RVR/CMV should not be used .... for any RVR minima less than 800 m. [AMC 10 (a)(3)]
and by definition any TAF will only have VIS
then anywhere CAT I is required, RVR 550 must be disregarded and VIS 800 used.
That's different from sonic's suggestion. Thoughts?
this leaves me perplexed.
The conversion factors for CMV, I believe, are 1.5 for daytime operations and 2.0 for night time operations assuming full lighting/facilities etc.
Let`s assume a CAT1 ILS at dest`n with a minimum published RVR requirement of 550m.
The way I interpret the 800 m limitation is that notwithstanding our 550 m RVR requirement we can`t `play` with an RVR below 800 m when conducting the conversion back to an equivalent met visibility.
Therefore at night: 800/2 = 400 and so the min forecast visibility in the TAF at ETA +/-1 hr is 400 m in order to dispatch with just 1 dest`n alternate.
For a daytime approach 800/1.5 = 533.3, so effectively the min met vis in the TAF at ETA +/-1 hr is 550 m (although in a TAF they forecast in 100 m increments so I guess you`d be looking for a minimum forecast vis of 600 m).
Anyway, it`s purely an opinion (and probably wrong!)
Any thoughts?