Reported Visibility and approach ban
 

Hi guys,

few days ago, in Genova (GOA/LIMJ), ATIS was reporting 3500 meters of visibility. The ILS (it's just CAT I) for runway 28 has this minimums for Cat. C: 788' DA / 3600 mt VIS (not sure about 788', maybe 789' but this is not the point :})

I was OFF but a friend of mine, a captain who was approaching GOA, told me about 2 airplanes in front of him landing there. As his turn come, the VIS increased above 3600 mt.

We know that if the RVR/VIS is below the minimum we can start the approach until reaching the Outer Marker. At this point, in order to continue, you need the actual RVR/VIS to be above minimum, otherwise a go around should be executed.

So, we thought about the 2 airplanes landing without having the minimum VIS and we came to this: as the reported Visibility is the lowest visibility of the 360° view from the airport, maybe at the outer marker they have already got the runway in sight because 3500 meters VIS was a sector not affecting the final for that runway and decided to land.

My question is, legally, are we authorized to continue beyond the OM if we don't have the minimum VIS but we have the runway in sight and we are able to maintain it? (note: Visual approaches are no longer granted in Italy).

This is something not stated in the EU OPS approach ban explanation.

Waiting for your thoughts and hints!

Where do you get those numbers from? That's not the DH on the ENAV plate, nor the correct VIS or CMV calculated from either.

Jepp chart for ILS rwy 28 at LIMJ shows an EU standard minima of 788'/2850m/3600m (ALS out) - but this is not the point :}

The golden rules:

1. Don't crash.
2. Don't do anything which (while you may get away with it) risks a crash.
3. Don't get caught.
4. Obey the letter of the law.

Letter of the law:

Appendix 1 to Ops 1.430, para 3, Visual Reference for Category 1 approach doesn't mention RVRs or visibility estimates - only various runway/threshold/lighting elements.

If, as you say, you have the runway in sight at the OM, then you could request visual approach and continue. Once you are in continuous visual contact with the runway, IMC minimums no longer apply.

I don't doubt that you can read a plate but do you know how that's calculated? It seems inconsistent with Appendix 1 (new) to OPS 1.430 which requires no increment to DH with ALS out and a 2400 m max RVR/CMV for an ILS approach in any case.

which I wouldn't argue with for a moment however

includes

OPS 1.405
Commencement and continuation of approach
(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).

Compliance with OPS 1.405(e) and the establishment of visual reference permitting descent below DH does not absolve the crew from the letter of OPS 1.405(a).

I actually agree with Bookworm on this one, plus there IS a practical aspect.

Being able to see the runway on approach does not guarantee acceptable minimum visibility closer in, due to slant-angle. Actual visibility often becomes worse once you enter a fog-bank, and the only place where actual RVR can be assessed is on the runway horizontally.

Which is why Converted Meteorological Visibility is such a daft idea. For an approach with low minima (Cat I, II etc.), with a transmissometer right beside the runway, the RVR will usually offer a good guide as to whether there will be sufficient visual reference to complete the approach from DH. But to determine whether a crew should be permitted to start an approach based on whether the tower can see 3500 m or 3700 m from their perch is just bad physics.

If we're talking about an ILS, then the aircraft is flying a steady 3º slope towards the runway, so the slant visibility will be steady all the way down, n'est Pas?

Admittedly it won't necessarily match the visibility along the runway ...

The minima for this Cat 1 ILS is 776' height above terrain. Descent angle is 3.17º, threshold crossing height is 56' (displaced threshold), so minima is (776-56=) 720' above threshold.

720/tan(3.17º) = 720 / 0.0553834597 = 13 000.2713 feet = 3 962 metres

400m meters for standard lights, and you need 3600 meters vis to become visual at the cat 1 minima :)

750m for the High Intensity Approach Lighting System, and you need 2850m to be visual with the lights at the Cat 1 minima. :)

There is no increment to DH, only to the required visibility - and the RVRs listed in the chart are system minimums - thus "2400m" is the largest value on the chart, but it isn't the "maximum" allowed - it's the largest "minimum" value allowed :)

Thank you for your opinions, but I have to clarify a point:

the ILS in GOA is an offset (2° left) ILS, with dangerous obstacles on short final (harbour cranes).

Regarding the Jeppesen chart, STANDARD with FULL ALS, you need 3600 meters VIS, minima is 788' DA.

You are approaching the Outer Marker (or equivalent position in this case, cause GOA has not the OM) and VIS is 3500 mt but you have the runway clearly in sight. What's your course of action?

Legally:

OPS 1.405
Commencement and continuation of approach
(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).

Pratically, 2 different airlines landed. Jeppesen minimums are not increased by our airline so they are the absolute minimums and are for sure the same as at least one of the other airlines that landed (LIDO).

LIDO minima are 780/800 baro for class B/C ("my" company LIDO manual uses 800/810). Visibility requirements are the same though except if using an EVS where it is 1500m/2400m.

Thank you Denti, I was referring to LIDO visibility requirements of "that" airline which is 3600 meters.

Short answer: If the tower is reporting runway visibility below the minima, you cannot continue past the equivalent point (1000' AGL).

Long answer: If the tower doesn't have RVR, then they are reporting a met vis, and you can factor this (if high intensity approach and runway lights are installed, x1.5 by day and x2.0 by night) so a "tower reported" 3500m airport vis becomes 5250m vis (for the purpose of continuing the approach). You still, of course, have to make the required (real, not "factored"!!) visual reference at or before the minima.

In any case, you seem to be looking for evidence of wrong doing in other operators in a specific case. Read the chart - the minima with FULL ALS isn't 3600m. It's 2850m.

Our jeppesen chart is different! It shows 3600 meters with FULL ALS.

I had a look to the LIDO's chart of another italian airline, and it's 3600 meters too with full ALS.

It seems jeppesen and LIDO don't trust in italian marginal visibility approach skills eheh :}

I don't have Jepp chart ready now, but I have the LIDO one:

http://i683.photobucket.com/albums/v...x82/goamin.jpg

Check,

You'd think so, but my experience has been different.

I've had the phenomenon of being able to quite clearly see the runway environs on the slope, only to have the percieved vis drop dramatically once actually in the mist. Can't give you a definitive explanation.

Say hello to redo for me!!

Well, if you have low fog/clouds you might be able to see the whole runway and airport at the FAF / FAP although reported visibility is down way below standard CAT1 visibility, but getting lower down, close to your MDH/MDA, you will see nothing.

Ok, today I flew to GOA. Jeppesen chart was recently updated in the minimums section and it now has 2850 meters as shown by Checkboard before.

Regardless, at ANY point on the ILS, if you sight the runway and make an assessment that you have the required VIS then surely you can continue based on this, are you not licenced to make this assessment.

Hi Ollie Onion,
Suppose the fog is just 50 feet deep.
From a point far out, you may be able see the runway quite clearly through shallow fog, because the light only has to travel through the fog a distance of 50/TAN (3degs) = 953 feet (or about 320 m). So if the RVR is 350m, then you'll be able to see all the runway easily.

During the flare, you'll be looking along parallel to the runway and will only be able to see 350m.

That's why we are licenced - to pay due regard to the reported RVRs.