RVR on DATIS

[Timothy]

Yesterday I picked up the KB DATIS which included "Visibility 800m RVR greater than 750m"

This is at an airfield which has an absolute minimum RVR of 800m on its ILS.

I understand that this is a DATIS, and that R750 is plenty for departure in anyone's money, but one of the requirements of a take-off in an RVR which is below landing minima is that you identify an airfield that is above minima within half an hour's engine failure flying. Therefore knowing whether the KB RVR is greater or less than 800m is actually rather relevant, even for departure.

So why would they record "Visibility 800m RVR greater than 750m"?

Will

[ATCO Two]

Because 750m is the maximum measurable RVR at Biggin Hill due to the physical characteristics of the runway. (Big hump in the middle).

[Timothy]

....what use is that if the absolute minimum for the ILS is 800m???:confused:

What if the Actual is "Visibility 500m RVR >750m"; How do I know if I am legal? Or is it just a matter of, you don't, but nor does anyone else? :E

Will

[ATCO Two]

The absolute minima for an ILS at Biggin Hill is actually 700m RVR.

[TEN-4]

W Collins
....what use is that if the absolute minimum for the ILS is 800m???

It maybe a good idea to get some correct Aerodrome data before you do your revalidation flight with an examiner! The absolute minima at Biggin Hill is 0700m RVR for an ILS approach to RWY21.

[Bright-Ling]

What if the Actual is "Visibility 500m RVR >750m"; How do I know if I am legal?

...because under 750m will be measured accurately with the lights seen. (Human observer method aka Fireman) :)

B-L

[Timothy]

....hmmmm....

On Jepp it's 800m!!! And the VOR/DME is 1200-1400m.

I couldn't see a reference in the AIP. Where is 700m published...is that Aerad?

But anyway the absolute minimum for single pilot ops is 850m, so the same issue applies!

Will

[TEN-4]

And the VOR/DME is 1200-1400m.
The VOR/DME is 1000m, same also for the LLZ only to RWY21.

[Timothy]

10-4

Pleeeze...pretty please

...what is your reference material?

Will

[TC_LTN]

Each ATC unit is responsible for calculating the minimum RVR values, for each type of instrument approach available at that airfield, below which pilots should not continue an instrument approach below 1000 ft above aerodrome level. The procedure was introduced on 1 March 1999, as a result of the CAA's consideration of the AAIB Report (1/96) into the accident to a Boeing 737 aircraft while making a Surveillance Radar Approach to Coventry Airport in fog. This calculated RVR value is the 'Absolute Minimum RVR'. The Absolute Minimum RVR is a theoretical value, calculated according to the instrument approach and facilities available at the aerodrome, which will be equal to or less than the specified operating RVR for a Category A aircraft carrying out that instrument approach procedure. The 'absolute minimum' RVR values are based on the calculation process notified in the AD 1.1.2 section of the UK AIP. If the minimum contains an RVR element which is greater than the aerodrome system maximum, or the unit is not capable of making RVR observations, a table is available from which operators are able to calculate an 'equivalent RVR' based upon the meteorological visibility and a scaling factor. In certain circumstances, for example, if the unit is not capable of making RVR observations, operators can calculate an ‘equivalent RVR’ using the meteorological visibility and a scaling factor. Detailed information is contained in the AD 1.1.2 section of the UK AIP. As far as I aware there is no requirement to promulgate these 'Absolute Minimum RVRs' outside the MATS Part 2 of the particular unit concerned. Since this 'Absolute Minima' will always be equel or less than the CAT A operating minima, the CAT A operating minima is really the only value which needs to be promulgated to crews.

The purpose of this procedure is to act as a merely a 'safety check' where a pilot may have made a gross error in calculating the operating minima for that approach. Should a pilot request details of Aerodrome Operating Minima or indeed the 'Absolute Minima', the controller will pass the minima published in the Aerodrome (AD) Section of the UK AIP for the particular instrument approach procedure. The controller will also advise the pilot that this is the lowest minima which would be applicable to a Category A aircraft flown by an instrument rated pilot in current practice when all the aerodrome lighting facilities are serviceable.

At the end of the day the decision to make an instrument approach in specific weather conditions rests solely with the pilot who must ensure that the flight complies with the appropriate legislation, including licence restrictions and Operations Manual requirements. Controllers are not permitted to prohibit a pilot from making an instrument approach other than for traffic reasons and they are not responsible for ensuring that Aerodrome Operating Minima are complied with.

[RodgerF]

Quote

But anyway the absolute minimum for single pilot ops is 850m, so the same issue applies!

Will, I think 800m is the absolute minimum for single pilot ops unless you have an ILS coupled AP that you can use down to DA.

R

[DFC]

Will,

I am also looking at the Jepp published minima;

ILS DME 21 - 800m RVR, ALS Out 1200m RVR
LOC (GS out) - Cat A - 1200m RVR, ALS Out 1500m RVR

I won't bother quoting the other approach RVRs.

There is no note to signify that RVRs are not reported above 750m

However RVR increments are 50m between 400m and 800m. Thus if the reported RVR is "above" 750m then it may be considered to be at least 800m since this is the next incriment above.

Single pilot ops are indeed 800m RVR

If one refers to the JAA Aerodrome Operating minimums published in the Jepp under Air Traffic Control and pages 601+, one will find a table for converting Met vis to RVR.

It does state that the table can not be used when reported RVR is available but I think that in this case, it is not avaialble above 750m

That table would be the basis on which I would make a decision regarding approach minima. In the example quoted, Vis 800m would for HIALS and HIRL work out as a "Calculated RVR" of 1200m.

Off to check the minima published in the AIP!!

Regards,

DFC

[Timothy]

Thank you, that is all excellent information. I feel a bit better now than 10-4 made me feel with It maybe a good idea to get some correct Aerodrome data before you do your revalidation flight with an examiner! The absolute minima at Biggin Hill is 0700m RVR for an ILS approach to RWY21. ...I'm pretty good about these things and have never had any difficulties with an IR, whether initial or renewal, and would be very worried if I thought that I had made a gross error as 10-4 implied.

I do have a mental block about that single pilot thing though. 2 Donkeys, Keef, Rustle and others keep telling me that it's 800m and...b:mad:r me if it doesn't keep popping out as 850m. Must get that particular neurone replaced!:uhoh:

I would still love to know the AIP reference, because I have looked through the entire "Aerodrome Specific" stuff on AIP and cannot see any reference to RVR. I've even cleaned my glasses :8 :O and that didn't help! I hope DFC does better than me!:\

Will

[TC_LTN]

WCollins,

Is http://www.ais.org.uk/aes/pubs/aip/pdf/aerodromes/30101.PDF what you are looking for?

I think Para 4?

[Big Hilly]

Hmm,

Interesting thread.

I have to confess that I was always led to believe that the absolute minima is 700m, I got that from a controller there, although he now works in the Midlands. Something to with them not being able to measure more than 750m due to the 'bump' on 21. :confused:

Perhaps Biggin SATCO could clarify though?

Best wishes,

BH

[TC_LTN]

Big Hilly,

The 'absolute minima' for Biggin Hill for use by ATCOs when initiating the safety check procedure are as follows;

ILS/DME Absolute Minima (RVR) = 700m
ILS/DME Absolute Minima (Met Visibility) Day = Not applicable
ILS/DME Absolute Minima (Met Visibility) Night = Not applicable

ILS/DME Localiser only Absolute Minima (RVR) = 1000m
ILS/DME Localiser only Absolute Minima (Met Visibility) Day = 670m
ILS/DME Localiser only Absolute Minima (Met Visibility) Night = 500m

VOR/DME Absolute Minima (RVR) = 1000m
VOR/DME Absolute Minima (Met Visibility) Day = 670m
VOR/DME Absolute Minima (Met Visibility) Night = 500m

As I tried to explain previously, these are 'absolute minima' for the initiation of a particular procedure by ATC and NOT applicable to a pilot in calculating his/her particular minima. As such, as far as I know, these 'absolute minima' are not published anywhere other than in air traffic publications or perhaps the aerodrome manual for the aerodrome concerned.

[Timothy]

TC_LTN

Thank you. I now see that 4.3.1 of the reference you gave me gives the figures referred to. I had sort of assumed that it would be published in the EGKB pages...obviously far too easy!

You would think, as RVR minima are considered the most critical information for a pilot making an approach (the only ones enforced by law), that the AIP editors might think of putting it somewhere on the approach plate!

We can but dream.

Will

[Big Hilly]

TC_LTN,

That's them!!!

Knew I'd heard those figures somewhere.

Many thanks,

BH

[TEN-4]

As I tried to explain previously, these are 'absolute minima' for the initiation of a particular procedure by ATC and NOT applicable to a pilot in calculating his/her particular minima.
One would hope that a pilot's minima would be higher than those TC-LTN quite rightly quoted for Biggin Hill. A pilot should not commence an approach if the visibility is less than those TC_LTN listed for this particular aerodrome otherwise ATC are required to use their legal jargon which is put aside just for very special occasions which go something along the lines as ''c/s, you are advised that the current RVR is *** meters which is below the absolute minima for a (type) of approach, what are your intentions'' etc etc. Should a pilot be a complete fruit cake and decides to continue the approach, ATC are then required to say (prior to completing a 1261 form) ''c/s, if you continue the approach it is belived that you will be contravening UK legisation and I shall be required to report the facts''.

Timothy: I agree with you regarding the figures (or lack of) in the AIP entry.

[TC_LTN]

Thank you. I now see that 4.3.1 of the reference you gave me gives the figures referred to. I had sort of assumed that it would be published in the EGKB pages...obviously far too easy!

You would think, as RVR minima are considered the most critical information for a pilot making an approach (the only ones enforced by law), that the AIP editors might think of putting it somewhere on the approach plate!

W,

Surely since the data at 4.3.1 is applicable to many locations you would not expect it to clutter up every individual plate but is best located in the Aerodrome General section? I would have thought the OCA was the most critical information for the particular approach which, of course, is on the plate.

Just a thought.

[Timothy]

Surely since the data at 4.3.1 is applicable to many locations you would not expect it to clutter up every individual plate but is best located in the Aerodrome General section? I would have thought the OCA was the most critical information for the particular approach which, of course, is on the plate.Jepp put it on every plate, and their pages are half the size of the AIP ;)

I guess that Jepp is designed for quick reference, whereas it is not unreasonable to struggle with the AIP a bit!

W

[SATCO Biggin]

I think ATCO Two, TC-LTN and TEN-4 have answered all the points on this thread, so there is little point in me putting in my 10 pence worth. I do wonder if the CAA haven't made things a lot more complicated than necessary by introducing another set of 'minima' (Absolute Minima).

Heres another thought for you....

RVR's at Biggin are assessed using the human observer method. That is, someone counts how many runway lights they can see from the 21 threshold. The maximum number of lights that can be observed is 13 due to the hump in the runway. A table produced for us by NATS Ltd lists this as an RVR of 750 metres. If ATC report the RVR as 'in excess of the maximum measurable (750 metres)' then the pilots have to calculate an 'Equivalent RVR' by factoring the Met Vis by 1.5 or 2.0 dependant on whether it is day or night.

How can Biggin ATC assess the RVR to be in EXCESS of the maximum we can see? We would need to see 14 lights to know the RVR was in excess of 13 lights!! So theoretically the RVR at Biggin can never be more than 750 metres because we cannot measure it and the pilots should not be factoring the met vis.

Regards

[Spitoon]

As has been pointed out, absolute minima is an ATC procedure and the values that trigger the procedure are, or were until TC_LTN popped them into his post, only written down in the unit MATS Part 2.

This really shouldn't be of any interest or concern to pilots because the only time the procedure is triggered is if a pilot looks like he/she is going to make an approach in conditions that are below all legitimate minima that can be calculated.

TC_LTN also makes the point that it's a final safety check or propmpt to the pilot that maybe someting is wrong with the minima that are being used.

It's undesirable to 'put off' the pilot just before he/she makes an approach in poor conditions with the official phraseology if ATC are wrong and the pilot is legally able to attempt the approach. But if it's legal to make the approach I've no doubt nothing further will be heard from the authorities - it's just that I can't think of a situation where an approach could legally be made and when the warning would be passed to the pilot.

[Timothy]

Spitoon

Really showing my ignorance here....

If the AIP says for the ILS 21 at Biggin in an "A" aircraft the minimum RVR should be 700m, why is Jepp showing 800m?

If I am a private operator (as indeed I am) I do not need to announce in my Ops Manual where I am going to get my RVR minima (on account I don't have an Ops Manual) so all I have to do (I assume) is remain legal.

So why shouldn't I use the minima as specified in the AIP and MATS Pt 2s?

And if I can use them, why not publish them?

Or have I missed an important line in the argument here?

(Let's leave out the confounding factor of the minimum 800m for single pilots for the moment.)

As ever, asking, not arguing,

Will

[TC_LTN]

W,

You haven't listened to a word we have said! ;)

The Absolute Minimum RVR is a theoretical value, calculated according to the instrument approach and facilities available at the aerodrome, which will be equal to or less than the specified operating RVR for a Category A aircraft carrying out that instrument approach procedure. This value is used simply for the initiation of an ATC safety checking procedure and does not relate to the minimum RVR calculation you would complete for an approach. The 'absolute minimum' RVR values are based on the calculation process notified in the AD 1.1.2 section of the UK AIP and in the case of Biggin ILS/DME result in a figure of 700m.

As far as I can see the AIP does not mention a specific RVR value for the Biggin ILS/DME procedure and you would 'simply' :eek: initiate the generic calculation on the basis of the data contained in http://www.ais.org.uk/aes/pubs/aip/pdf/aerodromes/30101.PDF
Using the table at AD 1.1.2 para 4.3.1 with a CAT A OCH of 280 and 420m of HI Approach Lighting I think you would arrive at a minimum RVR of 800m which I guess is what Jepp conveniently extrapolate and place on their plate for you.

So in summation, yes, you should use the minima contained within the AIP, which I think works out to 800m but you should not use the absolute minima contained within MATS Part 2 which is for the initiation of a ATC procedure and therefore we do not publish that value for your use.

I may have missed your point entirely - if so, I apologise - but this is the way I understand it!

[DFC]

Perhaps the following would explain the situation as I see it:

The minimum RVR for a pilot making an ILS approach is 800m in the Biggin case.

The maximum RVR that can be measured at Biggin is 750m

Even if the visibility is 100Km, the reported RVR will be 750m.

Thus an RVR reading of 750m can mean that

a) the RVR is indeed 750m; or
b) the RVR is 800m or more.

The pilot needs 800m and there is a procedure for determinimg the calculated RVR based on met vis.

ATC on the other hand are charged with reporting pilots who land below minimum RVRs.

In the Biggin case, ATC have no evidence that any RVR minima has been busted unless thay can show that the RVR was less than the required minima. The first time that ATC know the RVR is below the minima is when an RVR of 700m is reported.

To my understanding, that is why ATC are working with an "absolute minima" of 700m while us pilots are only interested in 800m.

Does that explain the situation?

Regards,

DFC

[Timothy]

DFC

Although what you say is entirely reasonable and sensible, as I understand the explanation it is different.

As I understand it there are simply two different ways of calculating minima, one of which applies to pilots flying approaches and the other to a theoretical minimum applying only to ATCOs who have to decide whether to warn pilots that they may be busting minima, and if they continue to do so then to file an MOR.

I understand that the second, the absolute minimum, will always be less than or the same as the first one, as applied by the slowest aircraft, "A"s.

So far so good...makes perfect sense to me. But the bit I don't get, and probably never will, despite my expensive education, is why two different criteria are used. Why does ATC not simply take the same criteria, as applied on our behalf by the gentle gnomes toiling away in the cellars of Jeppesen and Aerad, and use the most liberal of those as their criterion?

Despite all the valiant efforts of all these people who have been trying to explain it to me, that question remains.

Will

[TC_LTN]

Why does ATC not simply take the same criteria, as applied on our behalf by the gentle gnomes toiling away in the cellars of Jeppesen and Aerad, and use the most liberal of those as their criterion?

Despite all the valiant efforts of all these people who have been trying to explain it to me, that question remains.


At most locations the calculation would be the same but in the case of Biggin Hill, I believe for the reasons outlined by DFC, SATCO BH et al, it is reduced to a value that can be accurately measured.

[Timothy]

Bingo! I'm there. Thank you all!

Night night :zzz:

Will

[Timothy]

I'm so sorry to drag all this up again, but flying into Biggin today, on first contact with Thames, I was told "Biggin is reporting Met Visibility of 700m, which is below absolute minima for the ILS"

Now, I never argue with an ATCO, or anyone, and anyway it cleared up by the time we got there, but is it accurate to say that if the absolute minimum is R700 that a Met Vis of 700m is in the approach ban?

Timothy

[Timothy]

Talk to me someone....

AIP AD 1.1.2 says that I can multiply met vis by day by 1.5 if there is HI lighting.

AD-2-EGKB-2-1 says that RWY 21 has HI lighting

No RVR was available, only met vis of 700m, so surely I am entitled to interpret that as 1050m RVR.

Or am I continuing to show my ignorance?

Biggin SATCO, are you there, or AlanM, or .seven? Surely someone can answer?

[Legs11]

SATCO BIGGIN,

If you can see an object 'at ground level' beyond the last visible light then you are allowed to report 'RVR in excess of x' We have the same at my airfield, can't see lights due to a hump, but you can see buildings/ariels and therefore can use the 'in excess of' line. It's in CAP168 somewhere.

Any help?

L11

[TC_LTN]

I was at work last night and only read your post just now so can't ask any Thames valid boys but in the absence of any other replies and having read and re-read the Part 2, I would say you are correct.

If Biggin are not reporting RVRs, even if the Met Vis. is 700m or less this MET VIS should not be used to trigger the Absolute Minima Procedure and you would be entitled to use the 1.5 calculation.

Just to be sure;

It was the full ILS/DME procedure we are talking about?

The controller definitely quoted a Met Vis as opposed to an RVR value?

I will point out the thread to TC Ops and maybe we could issue a bit of paper to clarify this overly complicated procedure.

[AlanM]

Timothy......

Email me at home/and work! :)

(Damn that TC_LTN bloke is good...) http://www.stopstart.fsnet.co.uk/smilie/smileycowboy.gif

[Timothy]

TC_LTNIt was the full ILS/DME procedure we are talking about?Yes
The controller definitely quoted a Met Vis as opposed to an RVR value?I am 99% certain that's what he said and 95% certain it's what he meant. The RVR procedure at Biggin takes so long that I don't think that it could allow for new readouts every few minutes as I was getting (and indeed it was varying very rapidly in SCT000 !)

AlanMEmail me at home/and work!I don\'t have your work address, but I have eMailed you at home but...um...why couldn\'t you just eMail me?:confused: :rolleyes:

Timothy

[SATCO Biggin]

I have two days off from work and Timothy comes up with another question!!

Luckily a prominent member of my staff pointed out that this thread has re-appeared so I have dropped my Flymo and given this subject my full attention. :sad:

Now lets see.....RVR not available....its foggy....pilot needs to know whether he is breaking the absolute minima........

Well if anyone can come up with an alternative to factoring the Met Vis I would be interested to hear it!

(My pocket calculator makes the answer 466 metres Met Vis is equivalent to 700 metres RVR using the 1.5 factor, but ATC are not allowed to do the calculation, only pliots.)

Legs 11

Thanks for the tip. I will dig out CAP168 next time I am suffering from insomnia :O

[Timothy]

B SATCO

I am sorry to have interrupted the flymo...is that what you call the Yak now? :}

So, for the avoidance of doubt, if Thames report a Met Vis of 700m I am utterly entitled and legal to shoot an ILS/DME approach, but if they report R700 or less I am not and risk my details being sent to the Belgrano.

I am sorry that this has caused ripples in ATCO circles (as I understand it) but please believe me that this was an entirely innocent question asked without any overtones. I was not sure of the answer, and (perhaps naively) assumed that something I am told by an ATCO (who is working that approach all day every day) is more likely to be right than my part-time and amateur understanding.

I also, again naively, thought that I would just be given the answer and we could all continue to be friends.

Following a PM on the subject (which I have tried to clear up on the telephone with the author, but he seems unwilling) I will not ask any more questions on this forum.

I think it is a sad day for ATC/pilot relations, but there you go.

Timothy

[Farty Flaps]

If they are calling met v is and the chart limits are in rvr do the calculation..end of. Grey areas are for the use of all not just the regulators.

In some circumstance it can mean that in the absence of mid/stop servicable rvr thingies that it is better to go non lvp. Cant be arsed going into it but many a nite larnaca ahas been spent reading the necessary bits. After FHM ,sun et al have been exhausted that is:D

[PPRuNe Radar]

Following a PM on the subject (which I have tried to clear up on the telephone with the author, but he seems unwilling) I will not ask any more questions on this forum.

I think it is a sad day for ATC/pilot relations, but there you go.

A very sad day indeed. I am of course not privy to the PM and its contents, however if the said message was intended to discourage anyone from visiting this Forum and seeking answers to legitimate queries, then the sender is acting well outwith the bounds of their authority.

In fact, on Danny's trainset those with the authority to determine policy and access are small in number and try to keep communication lines open as far as possible.

Not looking for any names (hence no pack drill) and only know what Timothy has stated here. However knowing Timothy to be a man of integrity and a pilot who has always seemed to me to be keen to learn more about ATC and the various underlying issues and processes, then I find the notion that someone would take a stance to cause that to change worrying.

ATC 'professionals' who would behave that way aren't welcome here. My policy. Period.

[Timothy]

I now have heard, through the grapevine, why I was being vilified. It seems that the feeling was that I had waited months to "show up" Thames when they made a mistake, and was doing this for self-gratification.

Well, this could not be further from the truth.

My question was an honest one. I am a magistrate. I cannot be prosecuted or I will have to resign. If an ATCO says "The approach is below minima" I am not going to say (particularly without a copy of AIP to hand) "Oh, no it isn't, see you in court!" am I?

I think, and have said many, many times on and off this forum that Thames/LHR is one of, if not the best, ATC units anywhere. They bend over backwards to be helpful, they are precise, professional and I trust them with my life on a regular basis. I also beg favours from them (like tourist trips up the Thames) and they always say yes. Why would I want to put anything over them?

I have two friends on Thames, AlanM and another who I don't think is on this Forum, and I did not know if it was one of them who was talking to me. Why should I want to put one over on them?

I am also on friendly terms with Biggin SATCO. We have known each other for years. Why should I want to put one over on him?

I put a question in just the way I would have put a CRM question on the flight deck. That it has caused so much consternation between a pilot and an ATCO gives me cause for concern.

[SATCO Biggin]

I am also on friendly terms with Biggin SATCO. We have known each other for years. Why should I want to put one over on him?

...and no offence is taken from what you post (except maybe referring to Yaks as flymos, I though they were R22 helis).

Aviation regulation in the UK appears to be littered with 'grey areas' and sub paragrpahs of small text hidden in the deep murk of various documents. Often the answer to a question is not clear cut so those asking the question may get slightly varying answers from different people.

There are other threads on this and other forums specifically on the subject of regulation and attempted prosecution all of which identifiy parts of 'the rules' that you can drive a coach and horses through. You should try reporting someone for breach of Absolute Minima when a fog bank on the landing threshold of the instrument approach runway reduces visibility to diddly squat, but the other end is in clear blue sky. :confused:

[Timothy]

Doesn't even have to be end to end.

I have landed at EMA when the runway was in practically zero vis (I needed a follow me from the turn-off) but, because the fog bank was travelling North-South across the runway, the IRVR (which was only on the South side in those days) was giving >1500.

[almost professional]

timothy-our IRVR is still only on the south side, on the grass, clear of the strip and like all such installations subject to the usual anonomilies-bring back the human observer!

[Timothy]

Following off-forum multi-way conversations I can confirm that everyone is friends again, and (if I may) I will continue bugging you all! :O

[AlanM]

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hooooorah