Why no approach attempt in Wellington?

[breid]

About a month and a half ago I was scheduled to fly on a Pacific Blue flight from Wellington to Sydney. It turned out to be a very foggy day in Wellington and pretty much every flight was cancelled. However my flight wasn't yet and the good news was that they were airborne out of Sydney.
I was hopeful that they would arrive because the fog was starting to lift a bit to what I was guessing was a 200 foot (variable)ceiling and good vis underneath. I could see hills on the far side of the runway. However about an hour before landing it was announced that they were going to Palmerston North and my flight to Sydney was cancelled.
What I found odd was that they would not even try the approach or at least continue toward Wellington in anticipation of improving weather instead of giving up so early. However, I don't know how the rules work down there and was wondering what the requirements were to try and make it in. Perhaps the ILS was off the air.

[NoseGear]

The ILS at Wellington was on air, however, the DA there is 500ft, so you can see the waste of time trying an ILS with a clould base of 200ft. As for the legal side of it, you cannot start an approach if weather is reported below minimums, which it obviously was. The trip from Palmy to Wellington in a 73 would be on the order of about 10 minutes, so if the wx did the unlikely and improve, then it would have been easy to then head for Welly. It was an unusual period of wx for WN, usually just blows its tits off. Surprised Pac Blue did not get you all on a bus for Palmy and go to Sydney from there, its an international airport. Freedom go to Ozmateland from there, so obviously its long enough.

Nosey

[MOR]

So when is NZ going to join the rest of the world, where an approach ban is based on RVR and not cloudbase?

[cjam]

It has joined the rest of the world.

[Capt Fathom]

Not sure what your point has to do with this case MOR?
If the cloud base is 200', and the minima is 500', you're not going to see anything. Even if the vis is 10kms!

[MOR]

Well, not really. The cloudbase might be 200' at the field, but it might be 500' at a mile and a half or so from the threshold, which means that if you have the vis, you could land. There might be a big hole opposite Greta Point. The cloud might be thin enough to see the field (or the lights) through it.

The point is, that if you specify an approach ban exists on the basis of cloudbase and vis, you will miss out on landing when it would be entirely legal on the basis of visibility only.

That is why in Europe, the only basis for an approach ban is RVR for a precision approach, or RVR/vis for a non-precision approach. As long as you have the RVR/vis, you can continue to MDA/DA.

It is interesting that, when the TV cameras were reporting the recent fog at WLG, you could clearly see the 16 threshold area from the terminal. OK it may not have been the 3000m you need, I don't know, but as the ceiling was indefinite, you couldn't make an approach even if you could clearly see the runway lights through the murk.

When flying in Europe, on the days when the weather was close to minima, on about 50% of those days we would have never got in if there had been a minimum cloud base.

Mind you we normally just went Cat II, which got us down to 100' radalt. Only ever missed one of those...

BTW excuse me if the terminology isn't correct, been a while since I flew commercially in NZ. They keep changing the rules, I can't keep up. :p

[askmelater]

Nose gear, MOR:

Quote; “the DA there is 500ft, so you can see the waste of time trying an ILS with a cloud base of 200ft”

I would have thought not necessarily the case unless it was an overcast layer, broken layers can still provide the odd area of clear sky and whats to say that won’t happen around the runway threshold.

Quote; “As for the legal side of it, you cannot start an approach if weather is reported below minimums, which it obviously was”

I have interpreted minimums here to be both cloud and visibility (correct me if I am wrong) and I would therefore disagree with your comment. NZCAR Parts 121.159, 125.159 and 135.159 all state that the approach cannot be continued past the FAF (or final approach segment) if the VISIBILITY is less than that prescribed for the approach, no mention of cloud base and the fact the approach cannot be CONTINUED would suggest that there is no restriction on at least starting it. Again I would suggest that it is quite common for 5 to 6 oktas (ceiling/base) of cloud to provide sufficient gaps between clouds for visual reference (at the required minimum at least) to be maintained.

In NZ (not sure about other places) fog (FG) is used when visibility is less than 1000m and mist (BR) when visibility is between 1000m and 5000m. Granted the visibility in Wellington during that period was a lot of the time less than 1000m and therefore not suitable to continue an approach but there was nothing stopping an attempt to the FAF/FAP (unless operator specific procedures restricted it). The vis required for the WN ILS is 3000m (5000m at night on 34) and to my way of thinking it wouldn’t take much for an improvement from 1000m to 3000m (maybe wind increases slightly).

My point; there is nothing in the CARs that stop you starting the approach and continuing at least to the FAF/FAP/final approach segment. My comments have assumed that conditions indicated that at ETA, WN was forecast to be at or above the approach minimums refer 121.157, 125.157 and 135.157.

Interested on your thoughts and happy to be corrected on something I may have miss-interpreted.

MOR; so we do use visibility as a basis to continue approaches.

AML