Shallow fog and approach ban

[demomonkey]

For a CatI landing the visual requirements are quite vague in that you must only see any part of the approach/runway edge/centrelines lights. If passing 1100' on the approach or FAF and despite the iRVRs reading 400m, the pilot has full CatI visual requirements and the runway is in full and continuous sight then is it admissible to land?

[captainsmiffy]

Have seen the self-same fog phenomena on a few occasions at BRS myself. No fog on the rwy at all but only over the transmissometers. Much discussion as to what to do with the approach on the first occasion, with the older and more experienced captain in the RHS urging me to land and ATC implying that it was below minima....managed to persuade the ATCO, in the end, that his transmissometer needed looking at prior to the approach ban point so he declared it u/s and we landed with everybody happy. It is a stupid situation though and one where common sense should prevail. A case of where 'rules are for the guidance of wise men and the obedience of fools....'

[moggiee]

I got caught by this landing a VC10 at Gutersloh in the late 80s. ATC were giving 400m RVR which was OK for us because our military rules permitted a Cat I ILS at that RVR. We could see the lights from miles away and we made the decision to land when still some distance away (it was my landing). All was well until we reached the flare at which point we hit dense fog and the reflection from the landing lights blinded me. My landing was a bit firmer than normal due to loss of visual references and I found myself doing about 140kt with practically no view out of the front window. The fog was so dense that we missed our turn off but as it was only about 40ft deep, tower could see our tailfin sticking out of the top of it like some sort of landshark and were able to guide us. 10 minutes later the fog was all gone and the whole airfield was covered in a thick layer of dew.

To be frank, I reckon that the quoted RVR was more than a touch "generous" in fact I would be surprised if it was more than 200m and I'm sure that ATC were trying to help us out, but it gave us a false impression of what to expect. That said, if it had been quoted as less than 400m we would almost certainly have made a visual approach because we could see everything we needed from miles away!

The requirements for visual references give a great deal of scope for making that decision to land - the hardest thing could well be getting a civilian ATCO to approve the visual approach on the first place.

[aerobat77]

For a CatI landing the visual requirements are quite vague in that you must only see any part of the approach/runway edge/centrelines lights. If passing 1100' on the approach or FAF and despite the iRVRs reading 400m, the pilot has full CatI visual requirements and the runway is in full and continuous sight then is it admissible to land?

afaik basicly yes. when you have positive visual contact with the runway or approach lights you may continue to decision altitude. at decision altitude always the crew makes final decision if to land or not regardless of the reported RVR .

if you cannot see anything and the weather is reported below minimums you are not allowed to approach until DA.

of course at extreme low RVR reports you should be extreme careful even when you see the runway from far away since you may like described run into extreme shallow fog on flare , loose orientation and get into severe problems when you nearly made it.

[captainsmiffy]

...the point raised, though, was that the rwy was not in fog. Only the transmissometer was...the question is about the legality of the approach when common sense points out the shortcomings of the rules. We are not really discussing loss of visual in a shallow fog type of situation.

[aterpster]

captainsmiffy:

...the point raised, though, was that the rwy was not in fog. Only the transmissometer was...the question is about the legality of the approach when common sense points out the shortcomings of the rules. .

That is a very unusual condition. Even when it exists how does the flight crew safety and positively assess it; i.e., transmissometer(s) "fogged in" but the runway is "CAVU?"

[aerobat77]

the question is about the legality of the approach when common sense points out the shortcomings of the rules. We are not really discussing loss of visual in a shallow fog type of situation.

strictly due to law you may continue when you have a solid visual contact with the rwy or the app lights to decision altitude, and then finally decide regardless what the weather report says.

but i think its a theoretical situation that just the transmissometer is completely fogged with anything else good for a safe landing, never saw that in real life.

[captainsmiffy]

It very definitely is a real situation; have seen it with my own eyes. Mind you, been flying since 1986! Appreciate that there could be problems in assuming that it was only the transmissometer fogging-in but that was our situation indeed, and we could see BRS 27 from many miles away and could also see a small patch of fog obscuring the area south of the runway. This the transmissometers were giving very poor RVR measurements whilst the rest of north somerset was basking in a glorious evening sunshine. The controller, however, was a 'numbers man' and had not recently looked out of the window (am being kind here!). It took some persuasion before he finally relented and stated that the machine must be broken! This saved me a difficult decision as I was new to command and I had a right seat recently demoted captain who was urging me to land anyway! The ATCOs late decision saved me from a tricky call.....

[demomonkey]

Dammed if you do and dammed if you don't!

If you pass the OM/FAF/1000' point with RVR < 550m you have broken the approach ban despite being meeting all the requirements for a catI landing. Fail.

So if you do land, expect a call from 'The Authority' and if you divert expect a call from Dir of Flt Ops. Either way you're going to be short on the tea and biscuits front. Do like the idea of the proactive ATCO realising the paradox of the situation and declaring the RVR equipment U/S and thus allowing pilots to continue to DA. However from a flight safety perspective this approach whilst legally acceptable does require a cloud base to be of sufficient height to allow reasonable time to assess the lighting requirements. As such it should be treated with caution.

[jalbert1]

If you get passed an RVR then I'd be inclined to believe it.
It's on tape for a start and they're closer to the situation than you are.
Slant visibility and all that.Never nice to loose visual reference in the flare at 20 odd feet.
http://www.aaib.gov.uk/cms_resources...8%20G-VAIR.pdf

[RAT 5]

I can well appreciate the question and understand the frustration. It's generated by the apparent inability to use discretion, common sense and be flexible. Trouble is, and as noted by the stories, there are sometimes when you can land OK and some when you shouldn't try. How do you know which is when?
Myself, at SPL, crossed the OM at 3000' perpendicular to the rwy en-route to the hold. A/C CAT 1. RVR 500m. Oops. Last flight of the night and div was BUS. Fully visual with the full length of the rwy; tower 3km's from the threshold and zillions of feet in the air. What to do? Luckily a KLM was also inbd. Discussed if he was doing an autoland; luckily yes. Radar vectors to 4.5nm behind and a PIREPS on landing please. KLM declared that "RVR was well in excess of what was being given"; we declared visual, landed. Filed a report to effect and nothing heard. Lucky for us. But it was slant range visual at OM. Recently a colleague at GRO rwy 20 ILS, CAT 1, saw everything at DA. As PF (F/O) flared it all went very dark and correctly they made a G/A. landed on the other end NPA.
It is not an exact science and thus the multitude of answers. "Where there's doubt there is no doubt" come to mind. Saved many a foolhardy thinking pilot that one, and ignoring has cost many too much.
Finally the pilot at LTN, many moons ago, Christmas evening, CAT 1 a/c, RVR 300m. Flew overhead 3000', declared field in sight and requested visual. Granted, landed, CAA reviewed the meteo and landings a few days later. More than a slapped wrist I remember. Long before SAIR's etc. Back in the dark days of mission accomplished = star pilot. But he still had his come-uppance. Things are more legally framed and the risk to very high. Your defence has to be more solid than a politician's promise.

[captainsmiffy]

Gentlemen, when you are in the position that was posed here initially, and that I, too, recounted, then you will have no doubts about the approach. Slant range doesn't even come into it! If you are in widespread fog then, yes, agreed, take extreme care as you might be 'suckered in' and fall foul of the slant range etc - but the situation described was completely different. We were in CAVOK conditions, as was the rest of the county but a little light fog was rising from the damp grass adjacent to the runway. This is quite common in the UK near rivers, streams etc. Fog was not forecast and neither was it occurring except for a few feet around the transmissometer. This post is all about what to do when clearly there is a paradox from the RVR transmissometers.....they happen to be poorly placed and are very obviously giving erroneous readings (well, they might be giving a correct reading for their immediate environment but if they reside in the only small packet of fog then you have a problem!)

Without a sensible ATCO then you will be damned by the authority for making the approach and you might be damned by the company for not 'taking the common sense decision'! The only answer, insofar as I can see is to elicit the ATCOs help and get it declared u/s. Believe me, you will not be thinking 'slant range' etc in the described conditions; more like "WTF! Why doesn't he look out of the window....." This phenomenon is much more widespread than you might think in the UK in the autumn on those beautifully crisp, clear and cold days.

[bookworm]

strictly due to law you may continue when you have a solid visual contact with the rwy or the app lights to decision altitude, and then finally decide regardless what the weather report says.

Not according to EU-OPS:

OPS 1.405 (a) The commander or the pilot to whom conduct of the flight has been delegated may commence an instrument approach regardless of the reported RVR/Visibility but the approach shall not be continued beyond the outer marker, or equivalent position, if the reported RVR/visibility is less than the applicable minima (see OPS 1.192).
...
(e) The approach may be continued below DA/H or MDA/H and the landing may be completed provided that the required visual reference is established at the DA/H or MDA/H and is maintained.

The visual reference mentioned in paragraph (e) does not exempt you from the restriction of paragraph (a). If it did, the approach ban would be practically unenforceable from outside the cockpit, as the crew could always claim that they saw the lights despite the low reported RVR.

[TolTol]

Sorry to hijack the thread but I have another question regards the approach ban and it relates to paragraph (d):

(d) Where no outer marker or equivalent position exists, the commander or the pilot to whom conduct of the flight has been delegated shall make the decision to continue or abandon the approach before descending below 1 000 ft above the aerodrome on the final approach segment. If the MDA/H is at or above 1 000 ft above the aerodrome, the operator shall establish a height, for each approach procedure, below which the approach shall not be continued if RVR/visibility is less than applicable minima.

Does this mean that the commander is entitled to continue the approach past 1000ft even if the RVR is below minima, they just have to decide by 1000ft what they are going to do?

Thanks.

[captainsmiffy]

You can pass the approach ban point if you have the requisite RVR. Once past it, it doesn't matter what the RVR drops to but you must have the required visual references at your decision point in orfer to land.

This thread is about the rather unusual case where the RVR recorder lies in fog but the aerodrome is actually CAVOK. It is thus not legal to pass the approach ban point without clearing up the RVR issue with the ATCO..

[bookworm]

Does this mean that the commander is entitled to continue the approach past 1000ft even if the RVR is below minima, they just have to decide by 1000ft what they are going to do?

It's not intended to mean that, but the wording is awful, isn't it?! The intention, of course, is that the 1000 ft point substitutes for the OM for the purposes of paragraph (a).