iRVR and Minima

[Ethics Gradient]

A little ATC guidance please.

Recently we were inbound to a major UK regional airport when the RVR dropped below Cat 1 minima. No problems though , we were in a Cat 3b (0/75) aircraft. However when we ask for a Cat 3 approach we are told that the iRVR system has just failed, an engineer is on way to fix it but until further notice the airfield is Cat 1 only.
As we trundled round the hold we dug out our manuals and as far as we can determine could make an approach based on human observation of the TDZ RVR. The Mid and stop end are “no effect” in the degraded airfield equipment table. However when we prodded the controller he responded that his Airfield Ops manual required all 3 iRVR transmissometer thingys to be working for worse than Cat 1 and he could not offer us a Cat 2/3 approach. He said he would check, however before he could get back to us we ran out of gas and diverted.
We didn’t feel in a strong enough position to fight the issue, it had been a long day and there was a fair chance we were mis-interpreting our manual. Having had a sleep on it though I’m still comfortable that we could legally have made an approach based on our books.
So for future reference which book was right? (both operator and airfield are UK CAA approved)

[Spitoon]

Interesting. The problem is that both books are 'right' because they will both be approved by the CAA. Where you may be making an slightly iffy assumption is that Human Observer RVR was available. Many airports that have IRVR stop maintaining HO facilities because it costs money - you have to have the lights calibrated at least once every three years. It's not a huge amount of money in the big picture but IRVR is mature technology and is usually pretty reliable kit. And, of course, the humans who do the observing can be redeployed.....

I can't remember what ICAO says off the top of my head about Cat II/III but - as a pilot you'll no doubt know - in Cat I if IRVR is not available the met vis can be factored to give an equivalent RVR. I don't see why the same should not be possible in Cat II/III - but I guess if you do the risk assessment stuff maybe IRVR is preferred.

[issi noho]

Spitoons correct, it would require human observation which just don't really have a place in UK majors anymore.

Regards cat2/3, it would depend entirely on the operators approval from the CAA but you would have had to have made the most incompitant submission approved by the worst inspector following his christmas lunch the day before his retirement to have got an approval which didn't require multiple IRVR's.

By diverting you did the right thing.

[tired]

For info, from our Ops Manual (UK, (CAA-approved!) long haul operator)-

1)For Cat II/III Ops with no decision height (ie DH = 0'), "at least one RVR value must be available at the aerodrome".

2)Under "Failed and Downgraded equipment" - "Touchdown Zone RVR may be temporarily replaced by Mid zone RVR if approved by the State of the Aerodrome. RVR may be reported by human observations."

3) Stop end RVR is always advisory (ie not required).

So, multiple RVRs are not required - we only need Touchdown RVR to do a Cat IIIB, and it can be replaced by Mid point RVR. And a human observation is perfectly acceptable - but as said above, the chances of finding a major aiport with a human observer available are probably a bit slim.

t

[Ethics Gradient]

I hadn't realised that getting human RVR readings had become so difficult in the UK. How hard can it be to train a fireman to count lights? Er sensible answers only I'd rather not get moved to Jet Blast.

Our ops manual is the same as tireds which is pretty much a straight copy from JARs.
In this case though the airport must have had someone qualified as despite the iRVR failure they were giving an RVR of 450M. I'm still not sure what would have happened if we had insisted on making an approach, would we have ended up at the wrong end of an SRG investigation or should we now be asking the airport for our diversion costs back!

I get the feeling I might have to phone the CAA for a "definitive" answer, any suggestions who would be the person to talk to?

[throw a dyce]

Ethics,
Are you sure that the 450M was not the met vis.If the complete IRVR system fails then that's the only other option.
At EGPD we used to have manual RVR.When the IRVR system was installed,the 16 RVR hut became the Emergency Visual control room.Then a new location was found for that,so the 16 RVR hut joined it's brother on the bonfire.
The firemen stopped doing RVR readings here over 25 years ago.Our assistants took over the task,but when IRVR came in,all the staffing numbers changed to reflect what their main job is.
It's not often that the complete IRVR system goes down,but then s....t happens sometime,and we use met vis as a backup.
Don't come to PD today.We have the Haaarrrrrr again:cool:

[issi noho]

Tired

Check the definitions at the begging of your AWO section.

iRVR, if its anything like mine, is defined as the RVR determined at TD, MID POINT and STOP END.

That is not a definition of the defunct Human Obs system. It is fairly clear that the manual needs to be brought up to date to fully reflect the current operation.

Im pretty sure it would have been a MET VIS issued and nobody has mentioned 'factoring' which would probably have permitted a CAT 1 approach to be flown. (edit - sorry spitoon you did mention factoring- memory fade)

[issi noho]

CAP 168 Licensing of Aerodromes

Appendix 2A para 1.2

Where IRVR is not available; RVR for the purposes of cat 1 ops may be assessed by human observer. However, the human observer method of assessment of RVR is not permitted for cat 2/3 operations.

So that would seem to forbid it, in the UK at least, irrespective of your ops manual.

[Ethics Gradient]

Ah finally, thanks Issi.

Bit of a farce if one bit of the CAA is approving something that another bit forbids but then why does that surprise me. :hmm:

Helps to bail us out with the company who may raise an eyebrow at what appears (according to our books) to be an unnecessary diversion.

[Spitoon]

Ah, now issi and Ethics have taken the lid off something that I didn't want to mention in case it clouded the issue (if you'll excuse the expression).

CAP168 is, technically, a set of rules that you need to satidfy in order to get an aerodrome licence, issued by the CAA's Airport Standards Department, and it doesn't have a lot to do with how aircraft are operated - that's down to the CAA's Flight Operations Department and what they will approve in your company's Ops Manual (all this is, of course, valid for the UK). Now, the two departments do talk to each other but maybe not as much as they could.

In order to get an aerodrome licence you have to show that you expect to offer all of the requirements in CAP 168 but it is recognised that some things might break from time to time, in which case the airport issues a NOTAM and the pilots then decide what they can do guided by their Ops Manual. For example, if some of the approach lights fail most Ops Manuals will still permit an approach, albeit perhaps with increased minima.

It's not quite so clear what the text that issi quoted actually means. Is it 'You won't get an aerodrome licence that permits you to offer Cat II/III approaches if you don't have IRVR but if the IRVR breaks you can report HO RVR or met vis and let the pilot decide what to do' or does it mean 'No IRVR = no Cat II/III'. The interesting thing is that you'll get a different answer from different people at the CAA.

As a pilot, what matters is what your Ops Manual says and if it is unclear on this topic I guess you should ask for it to be clarified. Although, if ATC at the airport are told that they cannot offer Cat II/III approaches without RVR you don't get the option!!

Knowing how inaccuarate HO RVR can be, maybe it is best if IRVR is available but this leads on to another debate about whether it all makes any difference anyway because if you get to DH/DA and don't see what you need you'll go ound. Because minima are just a tool to control exposure to the increased risk associated with a go-around if there is no chance that you'll be able to successfully complete the approach and landing.......

[Ethics Gradient]

Aaargghhh, now I'm getting a headache.

So the core issue isn't what the CAP168 says , more what the airfields own ops manuals say?

OK , the problem is that, using our JAR Compliant, CAA approved ops manuals we load enough (just) fuel on the basis that we can do Cat 3b approaches and if certain systems fail (eg the iRVR) we can still make approaches. Now it seems we have to be conversent with the internal approved manuals of each airfield we visit, which frankly isn't going to happen.
Is there anyway of knowing at which airfields Manual RVR readings are possible and which do and don't apply these rules?

[issi noho]

OK, I accept your thoughts on the subject.

With reference to airline ops manuals, in the operational procedures they(mine) only refers to RVR as a generic term when discussing failures, however, it is implicit that they are really referring to IRVR when you read their definitions of IRVR/RVR several pages earlier in the preamble.

What we should really ask now is; Are there any Low Vis Ops approved airfields where the human observer method is available as a back up to an instrument system.

As a pilot all I want is to know is if it is legal to commence and continue the approach. I want it simple but this is a technical subject and I would like the manual to be more 'technically' correct. The failure tables talk about using the mid point rvr; it should say mid point irvr as the human obs system doesn't consider (generally) multiple observers.

I have to say my question bank for the next time I teach or check LVO has grown immensely following this thread.:)

[tired]

Ah, so CAA Airfield Ops, or whatever they're called, don't talk to CAA Flight Ops? Now why doesn't that surprise me...?! :ugh:

issi - my Ops Manual makes no mention whatsoever of iRVR, whether in the definitions or in the text - the only references are to "RVR". Therefore, as far as I'm concerned my manual allows me to make an LVO approach so long as I'm provided with an RVR (either touch down or mid zone), no matter how it was determined. Very disconcerting to discover we're not signing from the same hymn sheet as ATC.

If I were ever in the situation that Ethnic described and a "human" RVR was available but I was still refused an approach, I would file an ASR - maybe that would make the CAA's left hand converse with its right hand?

t

[surface wind]

Ethics Gradient

CAP 168 states that when when IRVR is not available, manual RVR is permitted for CAT 1 approaches only. CAT 2 and 3 not available.

REF CAP168 Appendix 2A page 1.

The airport Authority on this night had to remove CAT 2/3 capability and NOTAM such action.

You could then have made a CAT 1 approach, but then under 'Absolute Minima' rules, if the manual RVR was less than 550m we would have filed a report on your flight!

I've had this before where JAR and CAA do not tie up. LVPs is a bollocks at the best of times......so easy to get it wrong....

[Ethics Gradient]

You could then have made a CAT 1 approach, but then under 'Absolute Minima' rules, if the manual RVR was less than 550m we would have filed a report on your flight!


There was certainly no suggestion on our part of making a Cat 1 approach below minima. we're not like that lot at STN the other week if ya get my drift.

The problem we have is that based on our ops manuals we could LEGALLY make a cat 2/3a/3b approach. Trundling round the hold at 4000' burning contingency fuel is no place to get into a complex legal argument that has the potential of gettting you on the front page of "Flight International"

The failure was not NOTAM'd but then the fog wasn't forecast either.

The hold and diversion must have cost my company £12K, not including customer compensation and loss of goodwill.


If it had been some other failure what would have happened...

for instance : failure of ILS stby transmitter : no cat 3 but cat 1 or 2 is allowed.
no approach lights : we can still do cat3a or b as long as the DH is 50' or less. but no cat 1 or 2.

etc etc.

[Spitoon]

I don't think the driver of an aircarft needs to worry what the Aerodrome Manual says, or what the ATC instructions say - any more than the controller needs to understand what an airline's Ops Manual says. (Of course, it's nice to have an idea of what happens on the the other side of the mic!) What matters is what the Ops Manual says. The pilot will be advised, by ATC or NOTAM, if anything that the AIP says is there is not working or whatever and the pilot then looks to see what the Ops Manual says he/she can or should do.

What the controller has done in this case is to provide more information (good) that has then generated lots of questions and confusion (bad). Understanding how the rules are applied is good but should happen in an office or over a beer - not on the flight deck (or in the radar room).

For example, issi says that failure of ILS stby transmitter means Cat II is OK but Cat III is not. In the UK you probably wouldn't be told the nature of the failure but simply that the ILS is available for Cat II approaches only.

Back to the original events - if the failure was not NOTAMed I would suggest that you have good reason to complain. The provisions to not issue a NOTAM for short-term or temporary failures (I can't recall the actual words) are interpreted far too liberally by some airports - usually because some manager or other thinks it looks bad if there lots of NOTAMs for equipment failure at the airport!