Cat I approaches

[Rainboe]

Could a kind ATC-type lease have a look at http://www.pprune.org/forums/showthread.php?t=269562
and advise what is the policy on giving RVR readouts for an aeroplane carrying out a CAT I approach please?

[eyeinthesky]

I'm not an airfield ATCO, but in my experience if there are three RVR values (only available when IRVRs are available and not the human observer method) they are all passed. As JAR OPS says, you need to ensure that those which affect your planned landing performance are at or above your minima.

This is logical, as there is not a lot of point in landing on a runway where the T/D RVR is 550m, only to enter the fog bank half way down the runway at 80 kts with an RVR of 100m and career off the side of the runway!

Just for those who may not be familiar: IRVR= Instrumented Runway Visual Range calculated by those yellow 'daleks' you see facing each other beside the runway. It is virtually instantaneously updated.

Human Observer method= A person situated on a suitably elevated position at the T/D end of the runway counting how many runway lights they can see and converting that to an RVR. Updated as often as they do this and tell the Tower!:p

[Spitoon]

In the UK, the procedures manual for controllers says:3.5.1 A number of different IRVR systems are installed at United Kingdom aerodromes. The processors in some systems are programmed to automatically reduce in intensity, or suppress, the display of the mid-point and/or stop-end readings when the values are not operationally significant.
3.5.2 Unless a suppressed value is specifically requested by a pilot, the RVR reports transmitted are to contain only those values that are displayed at full intensity. The value of the Touchdown position is always displayed at full intensity and if no other values are at full intensity this is the only value which needs to be passed.
3.5.3 A description of the equipment, its use and any other associated liaison with the telecommunications section shall be included in MATS Part 2.The rules used to be the same everywhere (because every airport that had IRVR used the same equipment) but now each airport sets its own rules. From what I recall, in the old days the equipment used to be set up so that the TDZ was always displayed and MID and STP were supressed if they were more than 600m and more than the TDZ value. All of this was intended to ensure that when conditions were such that cat II/III ops were necessary because of the RVR, that all three values were displayed (and hence reported to aircraft). Nowdays, with all of the SMS stuff that we do at airports, theoretically we should make sure that whatever is reported is sufficient to support operations at the airport.
ICAO, in the Manual of Runway Visual Range Observing and Reporting Practices, helpfully says:5.5.4 All-weather operations require the provision of RVR, and the level of detail to be provided depends on the category of aerodrome operations. The detailed requirements for all-weather operations are given in regional air navigation plans as follows:
non-precision approach and Category I operations
- one site providing information representative of the touchdown zone;
Category II operations
- as for Category I, plus a second site representative of the mid-point of the runway;
Category 111 operations
- as for Category II, but normally with a third position representative of the stop-end of the runway, unless assessments at two sites are adequate for the operations planned.It goes on to say (although this doesn't make it a standard or rule)Because visibility can vary considerably along a runway, particularly when fog is forming, useful information can be obtained from multiple instruments even if only Category I operations are being undertaken.
After a quick look at ICAO Annex 3, 11 and PANS-ATM, I can't find anything that gives a definitive answer to the question....which suggests that it's a locally determined procedure.
ECAC did produce a document called 'Establishment of Common European Procedures for the Authorisation of Category II and III Operations' back in 1979 but I think this is now long gone and I suspect that the airborne bits have been subsumed into JAR-OPS. However, IIRC the document also covered ground aspects of AWO and may have covered RVR reporting procedures.
All this doesn't give you an answer I'm afraid but I hope it is of some use!

[Rainboe]

Thanks chaps. My reading of that is that anything worse than Cat I warrants full AWOPs with Midpoint and Rollout reports. So what is Cat I predicated on? Is it only Touchdown>550m, or MP and Rollout both >550m as well? When flying a Cat I approach, all I want to hear is one RVR report, and as long as it is >550m, it's legal. Officially one is supposed to regard MP and Rollout reports under Cat I as 'advisory' only. Last summer flying into Leeds with mixed Cat I and Cat III operations, under a Cat I approach, we were being given 3 RVRs. It is relevant because unless a pilot has done the AWOPs course and sim checkout, he hasn't learnt how to handle more than one RVR report. Also, limits on Landing plates and in aircraft performance manuals only mention one RVR figure. So how would you handle 800/200/50?

[Spitoon]

Phrases involving worms and cans come to mind here! Maybe that's why no-one else wants to have a stab at it - I, however, am made of sterner stuff!!

First point to make is that this is a UK-centric answer. One of the problems with AWOPs seems to be that because there are few standards each State does things differently.
On the ground we don't really think in terms of Cat I or II or III - that, by definition, is determined by the decision height that the crew will use....and only the crew know what that is (and please don't tell me what it is, it doesn't make any difference to the way that I work). Each airport has Low Visiblity Procedures (LVPs) which will be introduced in certain weather conditions (RVR or cloud ceiling). The weather criteria used to be specified nationally but now each airport will introduce LVPs as necessary to support operations at that airport. LVPs are intended to do two things - first, to limit traffic and certain activities on the manoeuvring area if the TWR controller is not able to see enough to control it visually and, second, to protect the runway and ILS signal for aircraft making Cat II/III approaches (assuming the ILS is suitable for such approaches). It is no co-incidence that that the triggers to introduce LVPs are such that normally they are fully in place by the time that an aircraft will need to make an approach below Cat I minimum. And most operators are waiting to hear "LVPs in force" before making an approach to a minimum below Cat I - although, in my experience, I have seen aircraft making a Cat II approach when LVPs were not in force and some crews that did not really understand what "LVPs in force" meant (to be fair, it is a good few years since I was asked so maybe this latter is not an issue these days).

I can't help feeling that LVP ops have become a bit of a mess in recent years. Not only do we potentially have different criteria for introducing LVPs at different airports but many now use different 'levels' of LVPs - typically introducing some of the restrictions that will be necessary in preparation and bringing in the full restrictions only when the weather requires it. In this way the airport can continue to use normal arrival spacing for as long as possible. The problem is that it means that much of the airport (ground handlers etc.) will think that LVPs are in force because thay are subject to LVP restrictions but operating crews and ATC will be working 'normally' because the weather has not actually gone below a particular criterion. Although this is really useful to maintain maximum capacity when the weather is hovering in and out of LVP conditions it is a recipe for confusion - and it has gone spectacu;larly wrong on at least one occasion to my knowledge (read about it here (http://www.aaib.dft.gov.uk/publications/bulletins/january_2006/boeing_757_3cq__g_jmaa.cfm))

As an aside, the airport operator is, technically, responsible for managing the airport LVPs although this responsibility is often largely or wholly passed to ATC.

Hope this explains some things!.