visibility and rvr

[aerobat77]

hello !

maybe you can help to clarify the question if the visibility or the rvr is crucial for a decision to perform a flight or not when both is stated in the metar ?

as we all know in CAT I you need 800 meter vis or 550 meter RVR ( jar ops) and currently you often have metar reports with a vis of lets say only 150 but simultany a rvr of 700 . is it legal to land under such conditions opertaing CAT I ?

i would say yes since the rvr is crucial and vis becomes only interesting when the airport does not give a rvr- but since i heared also opinions that no because you need 800 meter vis AND 550 rvr instead 800 meter vis OR 550 rvr i would like to hear what you think.

thanks in advance !

[Luc Lion]

aerobat77,

I'd suggest you re-read the 14 pages of
Appendix 1 (New) to OPS 1.430 - Aerodrome operating minima
in the EU-OPS1 regulation document.

page 70-84, available here:
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2008:254:0001:0238:EN:PDF

These pages are quite clear : all limits on horizontal visibility are expressed in RVR/CMV.
(“Converted meteorological visibility (CMV)”. A value (equivalent to an RVR) which is derived from the reported meteorological visibility, as converted in accordance with the requirements in this subpart)

The conditions for using Reported Meteorological Visibility after converting it to RVR/CMV is explained and constrained by the paragraph:

(l) Conversion of reported meteorological visibility to RVR/CMV.
1. An operator must ensure that a meteorological visibility to RVR/CMV conversion is not used for takeoff, for calculating
any other required RVR minimum less than 800 m, or when reported RVR is available.

Note: If the RVR is reported as being above the maximum value assessed by the aerodrome operator, e.g. “RVR more than 1 500 metres”, it is not considered to be a reported value for the purpose of this paragraph.


2. When converting meteorological visibility to RVR in all other circumstances than those in subparagraph (l)1. above, an operator must ensure that the following Table is used:

Table 11
Conversion of met visibility to RVR/CMV
Lighting elements in operation RVR/CMV = Reported met. Visibility ×
Day Night
HI approach and runway lighting 1,5 2,0
Any type of lighting installation other than above 1,0 1,5
No lighting 1,0 Not applicable




In short : limitations are in RVR.
In specific conditions, reported meteorological visibility can be used as a surrogate for RVR after conversion.

Luc

[Type1106]

Aerobat 77

I think you are confusing yourself here. The limitations on CAT1 are in RVR, not met vis; if the particular runway minima allow it you can make the approach in an RVR of 550m PROVIDED the approach is flown in auto coupled mode, or manually with a Flight Director, or with a HUD. If you don't have an auto couple capability or a FD or a HUD then you are limited to 800m RVR.

NOTE RVR - not met vis. The met vis can be considerably lower than the RVR figure, as you say, and it's why RVR was brought in in the first place; it is RUNWAY visual range NOT met vis as observed from the met office.

Originally RVR was obtained by a man in a hut alongside the runway touchdown point and he literally counted lights! Nowadays, of course, it is done by sophisticated light measuring equipment usually at 3 places along the runway.

Luc Lion gives the reference authority to convert met vis to RVR which is called Converted Met Visibility. This is only used if RVR is not available or is above (I believe) 2000m

Hope this clears it up

[Luc Lion]

Type1106,

about the limitation you quoted that CAT I approaches with an RVR of 500 m are only possible if the airplane is equipped with a suitable auto-pilot (coupled with the ILS) or with an approved HUD and that without this equipment the RVR has to be at least 800 m.
Actually, that limitation is only applicable to single pilot commercial operations (see page 77).

For multi-pilot operation (or general aviation operation), the first limiting factor is the availability of a full approach light system (fully operational).

Luc

[aerobat77]

thanks much friends ! so i can sleep calm again, its like i understood ( and have flown) - there was in these days just a little curiosity because some in our company claimed its not legal when our OPS sends us to an airport with vis below but rvr in limits.

we operate cheyenne III commercial, multipilot.

cheers !