When to update RVR in LVP
 

During LVP information about RVR is given to pilots. When do you update this information? How big a change calls for an update of the values provided?

In Uk RVR values are reported by ATC in real time, whenever any change from a previously reported value takes place.

I'm sure you know this but FWIW in general once we're below a 1000' any RVR values ATC pass are for information only.

If we have legal RVRs descending through 1000' then we're locked into those numbers and subsequent change is irrelevant ( from a legal POV). From that point down we're much much more interested in monitoring for any equipment failures and acquiring any visual references, if any are needed.

Back in the old days when IRVR was still new the CAA would monitor landings against the IRVR logs and pilots were threatened with prosecution.

Knowing this , I refused to pass a 450M RVR to an FK27 about to flare following an RVR of 600M but ensured that I put it on tape that the change had taken place during the flare.

We never had that 1000ft rule back then.

Another one from long ago... Trident landing at Heathrow in gin clear conditions. The IRVR suddenly came on with a very low reading so I read it out as I had to. The Trident crew asked if there was a problem with the IRVR and when I said there was not they said that they were bound to go-around and promptly did so. We heard that the IRVR system has been turned on for maintenance but nobody told ATC!

Mats PT 1 goes into quite clear details on all the requirements for passing and updating RVR/IRVR, including not indicating it better than reported, turning the lights down and all that jazz. Oh and reporting IRVR Won't necessarily mean you are in LVPs either.

For info the IRVR on the ATIS/METAR is in general a 10 minute average at the time the report was made so could be a 10 minute averge that's now 29min out of date. Dependant on SPECI updates but again you'd only here them on ATIS.

The live IRVR is again in general(does vary with type - a one minute average.

Key point was made by a pilot - they all just a magic number related to some other magic number for some policy - that someone one day might just change like getting rid of LVPs for low cloud, key thing is what the aircraft pilot doing - you could say it's raining lemons, by that point ruling factor(dependant on a/c minima) is do we see the lights/runway before we hit our other magic number someone made up.

What you report doesn't cause crashes it's what the weather actually is at that spot in space and at that moment in time!

IRVR values used for METAR and SPECI are 10 minute running averages. Live values displayed to ATC are 1 minute running averages.

But - the 1 minute average is only of the raw visibility, the MOR. Other RVR parameters, such as Background Luminance and Runway Light Intensity are monitored at least every 5 seconds and if they change the live IRVR will be updated immediately.

So if, for example, ATC change the brightness of the runway lights, the live IRVR value will change within a few seconds, the system will not wait until the next 1 minute MOR value is available.

I know this a northern hemisphere thread but for interest this how it works in Australia.

We have RV (runway visibility) which is by observation and RVR which is instrumented only. Our transmissometers are approved for fog and mist only. We don't use the term IRVR. Melbourne was the first and currently the only CAT III installation, Sydney has CAT11.

Knowing the approach ban and 1000 ft requirements, we asked the airlines what they wanted in the way of RVR reports. The answer was they wanted an RVR check on first contact with the tower and nothing after that. Rather than initiate a MAP due to a subsequent report, they prefer to get the first contact report and fly down to the decision height. On departure, an RVR report is passed after the aircraft reports ready, before crossing the holding point.

The procedure you described seem to have a significant loophole.. Is there any specific point along the approach segment where the first contact with TWR takes place?

10 mile final.

And so the word significant in my post above does not apply.:E

I have noticed the term IRVR in the UK at LHR. Is this different than RVR? Perhaps laser transmissiometer versus forward scatter light beam but in the end, basically the same thing?

Thanks, I wasn't aware that there is still a human observer method in the UK. I have not seen the IRVR term used anywhere else. In fact, the Jepp approach charts for LHR just use RVR(including for CAT II/III approaches) but the term IRVR is used in the reference pages. Not sure why.

Does the RVR minimum value for approaches at the bottom of the page just mean the lower of the RVR or IRVR value available?

Human observation? Is that someone in a shack near the end of the runway?

<<we asked the airlines what they wanted in the way of RVR reports. The answer was they wanted an RVR check on first contact with the tower and nothing after that.>>

In the UK, with rapidly changing visibility at times, the procedure above could be somewhat undesirable and potentially dangerous,.

Counting the runway lights is always the more accurate method of determining Visibility along the runway.

IRVR is a nice piece of kit, but it only takes a very localised reading at each site, and the algorithm converting the light reading into RVR always assumes a level of contamination (dirt, oil etc) on the AGL light fittings. Hence if your airport has a decent AGL cleaning regime, then your IRVR is probably probsbly reporting lower RVRs than is actually the case.

OK, then give it to us on short final(ie after final approach point) at which point we are allowed to continue if below the minimum.

Thanks.

At Farnborough at certain times of year, the setting sun shines straight into the transmissometer and gives a false low reading.

It would be interesting to know, what are the ATS rules for updating RVR in case of significant variations to the aircraft on approach.

Formally speaking, the reported values can only be disregarded by the commander if already below 1000 feet. (EASA (a)IR-OPS)

for the UK, CAP493 sec 3 chap 3 para 7

IRVR values are to be passed to aircraft at the beginning of each approach for landing and, thereafter, whenever there is a significant change in the RVR until the aircraft have landed. A significant change is defined as a change in value of one increment or more. The current RVR value is also to be passed to aircraft before take-off.
7.2
Even though a pilot may have received an IRVR value from the ATIS broadcast, controllers must ensure that they pass the current value as specified above.
7.3
When all three positions are to be reported to the pilot, they are to be passed as three numbers relating to touchdown, mid-
point and stop end respectively, e.g.
“RVR runway (designator) 650 —500 — 550 metres”.
7.4
If only two values are to be passed, they are to be individually identified, e.g.“RVR runway (designator) Touchdown 650 — Stop End 550 metres”.
7.5
A high degree of priority should be given to such broadcasts to ensure that current RVR information is provided to pilots with the minimum delay.

Thank you. My memory suggests that the increments are

<500 m: 25 m
<1000 m: 50 m
<2000 m: 200 m

Need to check the books to be sure, probably Annex 3? But probably some day later. :O