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LongLats
6th Oct 2016, 07:41
I was just looking at the Jepp plate for the 27L ILS at Heathrow and noticed that where you would usually see 0.8km as the visibilty requirement at the DA on an Australian plate, it only shows an RVR of 550m, then 750m and finally 1200m respectively under headings FULL, LIMITED and ALS out.

Can any international guys comment on what the difference is here? I'm used to thinking about minima as a visibility requirement from the air, however isn't RVR a visibility on the runway centreline? How can you make a decision on what the RVR is if you're not on the runway>

clear to land
6th Oct 2016, 09:42
RVR is reported via the use of a transmissometer and reported as TDZ,MID and Rollout. Usually all 3 are required but exception may be made for RO for the Rollout section only depending on your companies policy. These instruments provide a readout to ATC, and ATC provide them to the pilot. Depending on the type of Approach (II, IIIA or B), certain minima are required before proceeding past the Approach Ban Point (ABP) which will normally be either 1000' or G/S intercept depending upon the State. You must always check the RVR before passing the ABP. If minima are less than required before the ABP you can not conduct the Approach. If you have passed the ABP you can continue to the relevant minima.

donpizmeov
6th Oct 2016, 09:56
The RVR needs to be reported, on the ATIS and from ATC. If you don't have an RVR reading, you have to use the min Viz figures. So if you have RVR use 550m, if the reading is not available use 750m. Works well around the world.
There use to be charts to factor Viz to work out the RVR, but most are not allowed to use those anymore.
The RVR transducers are spaced at touchdown, midpoint and roll out ends of the runway.
Not sure if this answers what you were asking or not.

maggot
6th Oct 2016, 10:02
Sydney has it too....

AerocatS2A
6th Oct 2016, 11:14
I think he's asking how you decide at the DA whether you have the required RVR to land when the RVR is a runway measurement.

donpizmeov
6th Oct 2016, 11:44
You look out the window and make sure you see enough to complete the landing safely. Does your ops man give guidance of what/how many lights you need to see etc?
Its no different to landing at min Viz range.

LookingForAJob
6th Oct 2016, 12:16
Speaking as an ex-controller in Europe, here's my take on it.....

RVR is the controlling factor in whether an aircraft can start an approach, or continue it beyond a specified point. If the aircraft gets as far as DH/A, if the pilot has the required visual reference he or she can continue to landing, if not it goes around.

StudentInDebt
6th Oct 2016, 12:49
In the UK, and the rest of Europe, if at 1000ft/FAF the RVR or visibility is below the landing minima then the approach must be discontinued. There is no pilot discretion to "take a look" however, you may continue if he visibility decreases once you have passed the approach ban point. This concept has been adopted in Australia for CAT 2/3 operations.

oggers
6th Oct 2016, 12:58
What clear to land said is correct.

ICAO annex 6 pt 1:

4.4.1.2 An instrument approach shall not be continued beyond the outer marker fix in case of precision approach, or below 300 m (1 000 ft) above the aerodrome in case of non-precision approach, unless the reported visibility or controlling RVR is above the specified minimum.

..."reported" is the key word. You cannot go down and have a look. Also, you should not even continue to destination unless the forecast RVR indicates you will at least get into your alternate. As per the same reference. And according to pt 2 the same applies to GA :ok:

Under EASA you may continue the approach but not below 1000' unless the RVR is above minimum.

[edit; with a nod to StudentInDebt who obviously types quicker than me]
[James Albright explains all this well on his site code7700]

Hempy
6th Oct 2016, 13:29
c_t_l answered it. It's in the books.

edit: oggers beat me

RUMBEAR
6th Oct 2016, 13:50
Longlats

The key to understanding the difference between visibility and RVR is in the definitions of each. As you correctly state the RVR is measured along the runway ( which is where you will be looking ). If my memory is correct the definition of met visibility is the greatest distance that can be seen over more than half of the sky. So if vis is reported as 800m, then along the runway could be more or less than this value. Visibility is relevant for circling but not so relevant for runway aligned approaches!. Where I work, when RVR is not reported we convert Vis to CMV (converted met visibility ), which is considered almost the same as RVR.

As other posters suggest RVR is more of a check to continue past the approach ban point for a pilot assessment of conditions at the DA.

RVR will always be reported by ATIS ( or TWR ) when being measured during low vis ops. Pilots don't make their own assessment of RVR value.

LongLats
7th Oct 2016, 06:59
Thanks guys that answers my questions.

Mr Approach
7th Oct 2016, 08:08
There is also a value for a CAT 1 precision approach calculated by the Tower controllers based on the number of runway lights (at max intensity) an observer, normally the airport airside safety guy, can count from the threshold of the runway. This is Runway or Ground Visibility and is a guide to pilots for ILS CAT 1 approaches. CAT 11/111 requires RVR measurement equipment and in Australia currently only SY, ML and CB are equipped.