Alternate Minima Launceston (YMLT)

[jetstar1]

G'day all,

This question has been driving me mad for a couple of days, so hoping someone can put me out of my misery...

I bought myself a set of Jepps not long ago, and noticed something interesting while trying to get used to the new format... Alternate Minima at Launy...

When doing my IREX, I was pretty happy that Alternate Minima Ceiling is based on the Circling Minuma plus 500 feet. The circilng minima is based on a survey of obstacles in the circling area plus (depending on the performance category) 300 feet (correct me if I'm wrong). Since the circling area will be the same dimension for every runway, the circling minima should be the same for every approach (this seems to be the case for 99.9% of aerodromes, but still correct me if I'm wrong. Therefore, if the cicling minima is the same, the Alternate Minima should be the same on every approach chart. Just to make sure, I dug out the trusty Bob Taite IREX book last night, which confirmed that Alternate Minima should be the same on each approach chart for an aerodrome.

OK, if you are still awake, time for my question, based on a CAT B aircraft...

YMLT VOR Rwy 14R - Circle-to-land MDA(H) on actual QNH 1330'(768') [DAP Plate HERE or Jepp YMLT 13-1]
YMLT ILS or LOC Rwy 32L - Circle-to-land MDA(H) on actual QNH 1350'(788') [DAP Plate HERE or Jepp YMLT 11-1]

Question Number 1: Why is the circling minima for the VOR approach LOWER than the circling minima for the ILS?

YMLT Alternate Minima [DAP Plates above or Jepp YMLT 11-1] - VOR Rwy 14R on actual QNH 1268', any other approach (ILS Rwy 32L in our example) on actual QNH 1288'.

Now at this stage let me say that I realise this is pointless, because the Met man won't forcast the cloud base as between 1268' and 1288', but this leads me to question number 2...

Question Number 2: What is the Alternate Minima cloud base for Launceston? Or can you have 2?

Any opinions greatly welcome, thanks in advance.

J1

[neville_nobody]

The ILS vs VOR circling approach:
The circling minima is actually the same if you look at the 32L VOR and ILS
Its the 14R which is lower. I would guess this is because of terrain off the end of the runway? Not sure what buffers are put on the circling area.

The alternate minima's can change with approaches and if the Tower is open or not for your special alternate minima

[ForkTailedDrKiller]

If I have this right, you are comparing approaches from different ends of the Rwy, ie 14R VOR vs 32L ILS.

1) Therefore I would think the reason for the circling minima for the 14R VOR Appr being lower than the circling minima for the 32L ILS is terrain/obstacle clearance. My Jepp has brown bits close to the threshold of 14R.

2) I make the alternate minima for a Cat B aircraft with actual area QNH to be 1268' for VOR Rwy 14 R and 1288' for ILS Rwy 32L.

I see there is a special alternate minima given as 1200' - with 980' for VOR Rwy 14R and Rwy 32 not authorised. I assume that's for use with actual terminal QNH but I am still searching for the reference to that in Jepp.

I assume the difference is also because of terrain/obstacle clearance issues from opposite ends of the Rwy.

Dr

[Zhaadum]

With Jepps the alternate minima is published on the back of the airport chart, not on each approach chart. It is nothing to do with the circling minima. I would suggest you have "the cart before the horse with your approach to this matter".

While it is common for the alternate minima cloud ceiling to be equal to the NPA circling minima + 500' and visibility circling +2.0 km it is not always so.

[SmokingHole]

isn't special minima applicable when you have a pair of vor/ils in the a/c? ref AIP ENR 6.2

I make the alternate minima for a Cat B aircraft with actual area QNH to be 1268'

FTDK, if you're using area QNH, you must add 50' to the alternate minima. You cannot take off the 'shaded' 100' on an area QNH.

[jetstar1]

Thanks for the snappy replies Nev and Doc.

Let's just for the sake of argument say the Tower is closed, so that rules out the Special Alternate minima, and actual QNH is available from AWIS.

I am starting to think my assumption that circling minima is based on ALL obstacles in the circling area must be incorrect. I had a quick flick through the Instrument flight procedure design Manual of Standards (MOS) but couldn't find a reference for circling minima design.

Keep the thoughts coming,

j1 (frustrated VFR pilot on a less than ideal day)

[jetstar1]

Zhaadum,

With Jepps the alternate minima is published on the back of the airport chart, not on each approach chart.

Yes, I realise this... but the fact remains that there are TWO printed on the same chart.

It is nothing to do with the circling minima.

Are you sure about that? I would have to dissagree. From the MOS (link above), my bolding:

The general alternate minima must be calculated by adding the tolerance for the forecast ceiling and visibility to the circling minima (500 ft and 2 km).

[Mstr Caution]

In answer to Question one.

The VOR 14R Chart date is 30AUG2007.
The ILS / LLZ 32L Chart date is 15 MAR2007.

It is quite possible that should the Chart dates be the same then the circling minima's produced may have been the same.

The 14R Chart being the most recent, it may be quite possible that a more recent survey could have been conducted resulting in a lower circling minima.

As you acknowledge there is not much difference between the two minima's. If a higher obstacle was surveyed then it's probable that both charts could have been ammended reflecting the higher minima's.

With regard to question 2.

Zhaadum is quite correct, use the published alternate minima on the reverse of the aerodrome chart & check the conditions associated with it. That is which approaches the alternate minimum is associated with.

[jetstar1]

Mstr Caution you are a legend. That seems to make a lot of sense.

Interesting to note that the Jepp plates have the same dates, but I assume the DAPs are more authoritive in this case as they come straight from the procedure designer.

I found it quite curious that a less 'precise' approach should result in a lower minima. So assuming I could circle to 32L if conditions require, I can use the 14R VOR lower alternate minima for planning purposes?

[GreenerGrass]

Navaid Rq

Another possibility that was shown to me a while back is that the circling/alternate min is also based on the the required climb gradient for the missed approach. Cairns is a good example. I use DAP's and if you look at the CS NDB/VOR A & CS NDB/VOR B you will see they have completely different Circling & Alternate minima. If you look at the top right hand corner of the CS NDB A chart there is the requirement for a DME. This then allows the missed approach point to be further from the hills to the south of CS and not overhead the Navaid. This would permit a lower minima which won't infringe the missed approach climb gradient. I see the YMLT plates have the same sort of Navaid Requirments in the top right hand corner. Hope this also helps.

[Icarus53]

I think Greener Grass is on the money here - the ILS is the only approach with a missed approach tracking NW, while each of the others head to the SE followed by a reversal. With terrain clearance and performance requirements, it's probably coincidence more than anything else that the two minimas are so close together!

PS - those new MAs are a pain in the arse! These plates changed in the middle of company cyclics with single engine approach into LT. Most people got through on the old plates while the last few got stabbed with this more complicated procedure. Were the old MAs unsafe??? Heaps more steps on the DGA too. Not a whinge, just an observation!

[Mstr Caution]

I found it quite curious that a less 'precise' approach should result in a lower minima

The ILS is a more "precise" approach when flown to the ILS minima as far as getting you closer to the ground is concerned.

The ILS chart is also applicable to LLZ approaches to the circling minima.

As far as circling is concerned, whether it's a non precision or precision approach that gets you to the circling minima, the same result is achieved.

Notwithstanding the comments above regarding climb gradient requirements.

[Scurvy.D.Dog]

... I'll reply more fully tommorrow (if I can do so without Mrs Scurv catching me and breaking the computer ) .. suffice to say a bit of most of the answers above applies.
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Icarus53 ..... yer right to an extent ... the reason the MA's were redesigned that way was to provide an off to the best approach (ILS) for which most of the weather that would require a MA is generated from the NW. ... by doing them that way, the most likely option was provided straight up + ... terrain is less of an issue to the SSE, and the aid of the LOC is available. The extension of that, should a return to O/H be required for 14, the positioning nav to the VOR (via the NIE loc) enables straight O/H outbound for the 14VOR.
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The DME arrival reworks were largely a survey issue, also to provide the ability to manouver off the 009R to the north, new arrivals from the west and St Helens (mainly for the RFDS).
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.. next time you fly in .... have a captain cook to the north of the 14R threshold .... that is cocked hat hill ..... it could really **** up yer day if you are off the ILS pointed that way in the soup and a racket maker desides not to play .... same with the ridge to the NW and W .....
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... industry were canvassed about the MA options ....
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.. any other queries or questions, let me know, and I'll ask the horses mouth
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P.S
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Start using the Walker Intercept (from the 009 to NIE) vice O/H ... makes the ILS procedure (reversal) much more comfortable for all concerned

[pilotshorvath]

I too am still investigating an answer, but Mstr Cautions suggestion that:

In answer to Question one.

The VOR 14R Chart date is 30AUG2007.
The ILS / LLZ 32L Chart date is 15 MAR2007.

It is quite possible that should the Chart dates be the same then the circling minima's produced may have been the same.

The 14R Chart being the most recent, it may be quite possible that a more recent survey could have been conducted resulting in a lower circling minima.

is now null and void as looking at my charts (Jepps) all VOR NDB ILS charts are now dated 16 NOV 07 (EFF 22 NOV)

cheers.