SCQ CATIII

[nick14]

Hello all,

I have been looking into Santiago and discovered it has a CATIII approval for rw17. The CATII plate shows 2 MACGs and different minima. Now to me this means that there is something important about the missed approach. How can it have a CATIII approval, and if so what is the MACG? As there is no CAT III plate for this runway unlike other airports it is impossible to determine the minima and MACG. If it is a higher value then we would need extra performance charts in order to dispatch there with CATIII conditions.

[rudderrudderrat]

Hi nick14,

I would say from the info on the chart that there must be an obstacle close to the approach path which infringes the cone on the GA - hence the two minima and MACGs.
On a CatIII approach, if you GA at 50ft radio, then you'll be over the runway threshold and the obstacle would be behind you.

[mustafagander]

Nick,

If you are referring to SCEL/SCL Arturo Benitez Intl Airport, Santiago de Chile, there is in fact a Jepp Cat III chart. It is on the same page, 21-1A, as the Cat II approach.

This page has one minimum for Cat II, RA 100ft, and one minimum for Cat IIIA, RA 50ft. For Cat IIIB there is a note that the fail passive minimum is RA 50ft, otherwise RA 0ft. We have a company requirement for the missed approach climb gradient to be not less that 5.0%.

There is a shed load of obstacles on the approach path but all are OK with a 3* approach slope so the Jepp charts say. From experience they look mighty close though!

Should you be referring to one of the many other "Santiagos" in the world I apologise for wasting your time.

[BOAC]

No - he/she is referring to SCQ as posted.

Nick - I think the answer must be that some obstruction on the airfield falls into the g/a cone for CATII (before the threshold) but not for CAT III over the threshold, and thus a low g/a hradient might compromise clearance - hence the higher minimums.

No effect on CATIII but you should have somewhere in your company OPS manual a max wt for CATIII approaches which I believe requires a 2.5% gross gradient?

Where two gradients are quoted (as for your CATII) a lot of airlines stipulate you must use the 2.5% UNLESS the company airfield brief contains figures for the higher MACG.

The 'great unknown', of course, is if you g/a at, say 199ft radio at SCQ on a CATIII at max CATIII ldg weight (to give a 2.5% MACG) what will you hit?:eek:

[rudderrudderrat]

Hi BOAC,
max wt for CATIII approaches which I believe requires a 2.5% gross gradient?
It aint necessarily so...
http://www.blackholes.org.uk/PP/ZRH16.pdf
ZRH ILS 16 CATIII DH 50' requires 5% GA gradient to 1,000' AAL.

[RAT 5]

The CATII plate shows 2 MACGs and different minima.

Does any authority allow CAT 2 approaches with a failed engine? Note I didn't say single engine. If they do, and you approach with less thrust than normal for the G/A, could this be cause for a higher minimum? Or, could the required climb gradient for obs clearance need to be started with higher ground clearance so to clear the obs with the same gradient when at higher weights?

[BOAC]

rrat - I was talking in general terms. ZRH16 would be a 'special' case and in the ZRH airfield brief for you. After all, these cuckoo clocks can be quite tall.............................

[mustafagander]

Oops!!

Thanks BOAC

[nick14]

I was referring to SCQ in Spain.

Our performance manual only has figures for a 2.5% MACG on a CATIII hence the question. If the requirement for the approach was greater than this then surely under pans ops it would have to be stated on the chart?

Thanks for the replies.