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RVR and Visibility in ILS charts

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RVR and Visibility in ILS charts

Old 17th Jun 2018, 12:36
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RVR and Visibility in ILS charts

Hi there,

Letís say an airport reported METAR visibility 0200, RVR 750. The requirements to shoot the ILS approach requires CAT 1 of Visibility 800m / RVR550m, The airport only has CAT 1 landing. Iím able to meet the RVR criteria but not the Visibility criteria, am I able to shoot the approach?

How about dispatch stage? Do we need both the vis and RVR?

Thanks for your time

Last edited by extricate; 17th Jun 2018 at 12:59.
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Old 17th Jun 2018, 12:49
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I don't think that RVR and visibility will be reported at the same time. ISTR
I think, if reported then RVR is controlling. In the absence of RVR, visibility may be factored to arrive at an RVR equivalent.

Last edited by Meikleour; 17th Jun 2018 at 12:53. Reason: additional comment
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Old 17th Jun 2018, 13:06
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Originally Posted by extricate View Post
Hi there,

Letís say an airport reported METAR visibility 0200, RVR 750. The requirements to shoot the ILS approach requires CAT 1 of Visibility 800m / RVR550m, The airport only has CAT 1 landing. Iím able to meet the RVR criteria but not the Visibility criteria, am I able to shoot the approach?

How about dispatch stage? Do we need both the vis and RVR?

Thanks for your time
Speaking for the U.S. only, RVR is controlling when reported.
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Old 18th Jun 2018, 00:19
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For dispatch, we look at rvr too? Or Visibility is the criteria?
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Old 18th Jun 2018, 02:21
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At least in the FAA system dispatching a flight is based on forecasts. The reg actually says "weather reports or forecasts, or any combination.." But I've never seen a forecast with RVR predicted. If the flight is only 30 minutes or an hour the current report matters as much as the forecast but as the flight gets longer you're going to base your planning on the forecast. Unless you're going to Hawaii where the current METAR will be about the same all week.
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Old 18th Jun 2018, 05:03
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The metar stated 0200 RVR R750 though
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Old 18th Jun 2018, 05:49
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I agree with MIB...

As I have always understood it, and according to our Ops manual, at the briefing stage the TAF is “controlling”...... and I’ve never seen forecast RVRs.

At the briefing/planning dispatch stage any METARS you see might be half a day old by the time you are setting up for the Approach so in Longhaul at least they are almost irrelevant, though I appreciate there will be a different emphasis on shorthaul.

In flight METARS/reported actual weather comes into play.....As for “shooting” an ILS....the reported RVRS only are controlling.

Last edited by wiggy; 18th Jun 2018 at 06:19.
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Old 18th Jun 2018, 05:50
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You won't be given that by the tower you just get a single value or the 3 values.

Your getting confused between preflight planning and inflight.

Metar RVR does matter in planning for say LVO on departure and you need a take off alternate or not and same for TO alternate selection.

It would help if you tell us your experience level and if this is you trying to get your head round it for exams or for real life operations.

Oh and as wiggy states above... there is a difference between what type of flying you are doing. Regional stuff with flight times between 40mins and 1.5 hours we will factor in the current metar but there is no legal requirement to do so. IT would then be a commercial decision to stick extra fuel on and go and hold till it clears up or sit on the ground and wait until the sun comes up.
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Old 18th Jun 2018, 06:05
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RVR is not forecast in a TAF. So you require your destination met. vis. to be forecast at or above your required visibility to depart with a single alternate. The only exception might be a very short flight (<10 minutes) that would be covered by the TREND in the RVR values contained in a METAR or SPECI report. But if you start getting as cute as this you should start asking yourself why. Also, don’t forget you can always start an approach but you may not descent below 1,000’ AAL unless you have the required RVR (or vis.).

PM
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Old 18th Jun 2018, 06:06
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Thanks for the explanations above. It makes sense now. Agreed that Metar shouldn't come into place for dispatch planning for determining landing operations into destination since it's validity would have expired. TAF should be controlling in planning stage.

is there anywhere written that given both visibility and rvr, rvr is controlling on whether it is legal to shoot The Approach?
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Old 18th Jun 2018, 06:13
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It should be in your ops manual. Once your into LVP's the controllers will only pass RVR's visibility won't be mentioned. When that swap over starts is airport dependant.

I have never ever heard a tower controller say RVR 550meters visibility 200meters wind variable at 2knts cleared to land. I have only been doing it for 17 years. I am just a young pup compared to Wiggy and PM.

Also there is a conversion table where you can convert visibility's into RVR's so say the airport RVR is off line and they give out a viz instead during daytime that table would convert 400meters to 400 meters at night it would convert to 600meters RVR. So daytime you wouldn't be able to go past the approach ban limiting factor and at night you would.
I can't remember the table off the top of my head I have used it 10 times in the space of 17 years never in the last 10 years But I know where it is in the manuals and what to do with it. So don't take my example as the actual factors day and night. There is runway lighting factored in as well.
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Old 18th Jun 2018, 06:16
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My manual states an approach should not be commenced unless either reporting visibility OR controlling rvr is at or above operating minima. Grey area here

What happens if atis states vis is below but rvr is above minima? Usually Cat 1 visibility 800m and rvr 550m. If vis is 700m and rvr is 750, which one do we fall back on? I'm thinking rvr
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Old 18th Jun 2018, 06:23
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Originally Posted by extricate View Post
My manual states an approach should not be commenced unless either reporting visibility OR controlling rvr is at or above operating minima. Grey area here

Ah, having read the above is the “grey area”/the confusion down to the way the Ops manual is written/semantics? For some approaches the “controlling” minima will be a vis....for others it will be an controlling RVR...however the way the manual has been written has conflated the two.

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Old 18th Jun 2018, 06:32
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And you would be correct. But you will never have a controller give you both. It will either be vis on the ATIS and the subject never mentioned again. Or the approach controller/tower will give you a RVR value they won't give you both.

I will add this only works for controlled aiports if you ever start operating into Information service airports things sometimes get a bit weird you should get special briefings before you do and at that point if its not mentioned you can ask the question to your Chief pilot. technically you can just take the RVR but they may have different ideas.
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Old 18th Jun 2018, 09:08
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Thanks all
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Old 18th Jun 2018, 09:49
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Our ops manual states you cannot use conversion tables for minima below 800RVR after conversion. Hence I have never seen much use of this table.

For dispatch we are to use met vis only, again according to our manual.
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Old 18th Jun 2018, 10:02
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its that for takeoff requirements and alternates as well?
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Old 18th Jun 2018, 16:26
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Originally Posted by tescoapp View Post
its that for takeoff requirements and alternates as well?
This is what EASA says:
  1. A conversion from meteorological visibility to RVR/CMV should not be used:
    1. (1) when reported RVR is available;
    2. (2) for calculating take-off minima; and
    3. (3) for other RVR minima less than 800 m.


As for alternates, no special provision AFAIK. Why should there be?
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Old 18th Jun 2018, 16:36
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Sorry crossed lines. I wasn't on about the table.

It was using met vis only for take off mins and take off alternate selection when RVR is available.
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Old 18th Jun 2018, 21:09
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Hereabouts, the "visibility" generally refers to the "prevailing visibility" which is defined as the greatest visibility through half of the horizon (not necessarily contiguous).

RVR for a runway to which one is making an approach takes precedent.
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