what is controlling, RVR or Visibility?
 

While enroute to Frobisher Bay CYFB the other week the weather was reported as follows: 1SM R35/1200V3500FT/D -SN VV010 RMK SN8

I read that as, 1 statute mile visibility, Runway 35 RVR 1200 FEET VARIABLE TO 3500 FEET, (/D?), vertical visibility 1,000 feet (SN8?)

If I remember correctly, the RVR were below minimums but the visibility was adquate. The Jepps state that the RVR will be automatically be reported when the visibility goes below 2 statute miles.

I erred on the cautious side and said the airport was below minimums but I cannot find the regulation that would confirm that. FAR 91.175 only refers to "flight visibility".

Anyone run into this lately?

Thanks in advance!

http://www.faa.gov/library/manuals/a...a/CH%2002a.pdf
RUNWAY VISUAL RANGE
Runway visual range (RVR) is an instrumentally
derived value, based on standard calibrations,
that represents the horizontal distance a pilot will see down
the runway from the approach end. It is based on the
sighting of either high intensity runway lights or on the
visual contrast of other targets whichever yields the
greater visual range. RVR, in contrast to prevailing or
runway visibility, is based on what a pilot in a moving
aircraft should see looking down the runway. RVR is
reported in hundreds of feet, so the values must be converted
to statute miles if RVR is not being reported.
[Figure 2-11] This visibility measurement is updated
every minute; therefore, the most accurate visibility
report will come from the local controller instead of a
routine weather report. Transmissometers near the runway
measure visibility for the RVR report. If multiple
transmissometers are installed, they provide reports for
multiple locations, including touchdown RVR, mid-
RVR, and roll-out RVR. RVR visibility may be reported
as RVR 5-5-5. This directly relates to the multiple locations
from which RVR is reported and indicates 500 feet
visibility at touchdown RVR, 500 at mid-RVR, and 500 at
the roll-out RVR stations. RVR is the primary
visibility measurement used by Part
121 and 135 operators, with specific visibility reports
and controlling values outlined in their respective
OpsSpecs. Under their OpsSpecs agreements, the operator
must have specific, current RVR reports, if available,
to proceed with an instrument departure. OpsSpecs also
outline which visibility report is controlling in various
departure scenarios.

Canada's RVR regs are a bit o a mess these days!In essence RVR is controlling (1200A600B)unless the RVR is'fluctuating'ABOVE and below the LEGAL 1200 limit.In the fluctuating case one needs 1/4 mile Vis..
In your case the RVR was'fluc' between 1200-3500,and you had 1mile vis..Legal to proceed to land...
The most recent reading of Air Reg 602-129,used to say 'if the fluc'were above and below limits one could legally land(AIC1/97)..The latest 'mess' is the requirement for the 1/4 mile vis in the event of RVr fluc'..
AIM 9.19.2 Approach ban:ok:

Thanks oldebloke! That was the first instance I ran into that sort of thing. I will look up those Canadian regs you quoted and see if I can understand them. the reports did change every few minutes and we were able to land when the RVR went up again. The visibility was pretty good when we did land. Thanks again, that was a great help.

Art