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CAT II with DH>200ft?

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CAT II with DH>200ft?

Old 28th Aug 2015, 22:01
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CAT II with DH>200ft?

Hi,

Im getting confused with a CAT II chart that I have just found. This airport in Spain (EU) used to have a CAT II approach. Recently, there have been a few changes to the runway and also new obstacles have appeared, so the charts have been updated.

It shocks me to see this ILS CAT II with DH greater than 200' (between 233' and 276') . How is this possible? I thought both in the US and in EU CAT II meant 100'<DH<200'.

This implies that the pilot must get visual contact when s/he is around 1km from the threshold, so at that point there is a valley that is more than 240' deep and RAs are around 500'; is the radioaltimeter reading accurate in that case?



Many thanks
EnxAero
P.S. I am not a pilot, but an airport engineer, so I would move the thread to a different forum if necessary.
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Old 28th Aug 2015, 22:16
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Higher than typical Cat II minimums are due to the missed approach climb requirements; if you notice A/C that can perform a 5% missed approach climb gradient are allowed to descend lower Vs those that can only make 2.5%
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Old 28th Aug 2015, 22:19
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From Eu OPS: "Where the decision height (DH) and runway visual range (RVR) do not fall within the same category, the RVR will determine in which category the operation is to be considered."

DH could be limited to a higher height due higher OCH , however RVR is always the governing factor to determine the ILS category.
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Old 28th Aug 2015, 23:26
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Old 28th Aug 2015, 23:56
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Astra driver,
Indeed. One the modifications was the displacement of the threshold, so now the beginning of the runway is closer to the most critical obstacle in the missing approach. My surprise comes from the fact that even with a 5% gradient the DH > 200 ft.

Citation2,
I have found the sentence you mention in the context of determining whether it is CAT IIIA or CATIIIB.
However, for CAT II the definition seems to be:

‘Category II (CAT II) operation’ means a precision instrument approach and landing operation using ILS or MLS with:
(a) DH below 200 ft but not lower than 100 ft; and
(b) RVR of not less than 300 m.

http://eur-lex.europa.eu/LexUriServ/...01:0238:EN:PDF

Condition (b) is met, (a) is not.

Furthermore, since there are only 420 m of lights, I guess at least 700 m of RVR would be required.
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Last edited by EnxAero; 29th Aug 2015 at 12:55. Reason: Fixing link to EU Ops
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Old 29th Aug 2015, 09:08
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Is there a CAT 1 ILS on this runway? If so what is the DA & RVR? The only parameter that meets CAT 2 is <550m RVR. It is an odd ball. CAT 2 ground installations have other specifications than a CAT 1. It seems a lot of bother for 100m reduction in RVR. However, the CAT 1 RVR may be much higher than 550m.
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Old 29th Aug 2015, 11:13
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As RAT 5 suspected, CAT I RVR varies between 1300 and 2400m depending on aircraft category and missed approach climb gradient.

CP
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Old 29th Aug 2015, 11:36
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RAT5,
There is a CAT I equipment with DH ~550 ft. That is a funny one as well: for categories B, C & D the DA of the LOC approach is lower than with ILS CAT I. (In fact the ILS CAT I DA is even higher than the DA of the VOR approach).

I have no idea where the RVR of 450 m for the CAT II is coming from, as this is clearly not enough: When an aircraft reaches the DH of 233' (best case scenario for a category A aircraft), the distance to the threshold is (233-54)*0.3048 / tan(3º)= 1041 m.
Since there are only 420 m of lights before the threshold (IALS), even a RVR of 550m would not be enough, since 420+550= 970 < 1041


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Old 29th Aug 2015, 20:41
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Having had a careful look at the AIP I believe this should be a “Lower than Standard Category I Operation” (that is "A Category I Instrument Approach and Landing Operation using Category I DH, with an RVR lower than would normally be associated with the applicable DH."). The aircrafts would need to be approved for CAT II and capable of a climb gradient of 5%, but the DH would be determined by baro altitude.

But let's say that I am wrong and this is a CAT II. There is no inner marker and the RA for a category C aircraft is 514'. Are GAs going to be performed the first time the radio altimeter reaches 514', which should be ~1.6 nm (~3 km) before the threshold? If that is the case the ILS CAT I and even the VOR procedure would let aircrafts get a bit closer to the threshold.

One final doubt: If the aircraft is capable of only a missed approach climb gradient of 2.5%, when do we start the GA? There is no RA for that case.

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Old 29th Aug 2015, 21:54
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Wink @Inbalance, your Posted Pic

Sir,
I'm not able to identify the location of this image, but what a joy it is to view. It looks much like SW Germany. If you don't want to share the details in public, a PM would be sincerely appreciated. What a beautiful place it is! Standing by for PM if that is your choice. Thank you. NFZ
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Old 29th Aug 2015, 22:08
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@No FLy Zone, pic

@No FLy Zone
The pic is from the NW of Spain. That is the view from the cockpit approaching the runway 21 of LECO (A Coruña, Spain), the airport whose charts are mentioned in the thread. The pic shows runway 22, but it was renamed a few years ago.
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Old 1st Sep 2015, 03:38
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What I can't get my head around though is the increased Baro Alt minima for a regular CAT I approach, for which the decision point is not determined by reference to the Rad Alt...
That typically means there is an obstacle somewhere along the ILS flight path, at an altitude below the LOC MDA but penetrates the protection surface of the 3.00 degree ILS.

Remember that while the LOC MDA is a "hard deck", the ILS has to provide protection even if the aircraft is flown below the glide slope (up to full deflection), and below the DA when a missed approach is initiated. So near the runway the ILS protection is actually below the MDA in this case.

Additionally, the ILS design has to take into account that a real-life glideslope doesn't precisely signal the ideal flight path but may have some errors up and down due to reflections, etc.

When there are obstacles penetrating the ILS surface, the two basic choices are: 1) raise the DA(H); and/or 2) raise the glideslope angle beyond 3.00 degrees.
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Old 1st Sep 2015, 14:03
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Quote:
Remember that while the LOC MDA is a "hard deck", the ILS has to provide protection even if the aircraft is flown below the glide slope (up to full deflection), and below the DA when a missed approach is initiated.
Hi FlyerGuy, sorry if this is thread drift but your quote in bold is interesting to me... This has been the source of several discusions I've had with no resolution. Does the ILS really guarantee protection in the missed approach if the missed approach is initiated below DA? What about engine out? And do you have a reference for this? Cheers.
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Old 1st Sep 2015, 21:23
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@Derfred

If the missed approach were initiated below the DA the protection in the missed approach would be reduced, as you are starting the segment lower and closer to the obstacle.

I guess what peekay4 means is that if you started the missed approach at precisely DA, the aircraft still loses a bit of altitude until you it starts to climb, and it goes slightly below DA. Those few ft are taken into account and the aircraft is protected.
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Last edited by EnxAero; 2nd Sep 2015 at 08:49. Reason: fixing grammar
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Old 1st Sep 2015, 21:36
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As a quick graph to give some clarity, I have drawn a few lines over the obstacle chart (from the AIP). The original numbers in black are in meters. My numbers in purple are in ft. The horizontal axis is distance in meters to the end of the runway (so 2188 is the threshold)


Because of the deep valley (~260'), the radio altimeter height around the DH point is higher than when flying over the hill
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Old 2nd Sep 2015, 00:32
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Hi EnxAero I'm not sure that is the right chart to use. That "Type A" chart is mainly used for take-offs. So that particular chart is actually for RWY 3 departures instead of RWY 21 arrivals. The maximum heights shown on that chart may (or may not) actually be on the relatively narrow localizer path.

There is another ICAO chart called the "Precision Approach Terrain Chart" for use with CAT II and III approaches.

This "PATC" chart is used to asses any terrain which may impact the Radio Altimeter, but only to a maximum distance of 2000 meters. So basically, anything over 2000 meters gets ignored.

PATC for LECO RWY 21: http://www.aena.es/csee/ccurl/341/10...CO_PATC_en.pdf.
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Old 2nd Sep 2015, 02:52
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If the missed approach is initiated below the DA the protection in the missed approach is reduced
ummmm....MA below the DA?

Last edited by underfire; 2nd Sep 2015 at 03:14.
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Old 2nd Sep 2015, 08:48
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peekay4,
In general you are right, but for this particular case it more or less works, as in both cases the profile is done along a straight line.

http://www.enaire.es/csee/Satellite?...&ssbinary=true

AOC is not as precise, and the horizontal distances are to the threshold of runway 21, but it was a schematic drawing to give people an idea of the terrain before the threshold.

The "issue" with the PATC in this case is that, although it shows the deep valley at around 1000 m for threshold, it does not show the peak of the hill 3000 m before. You can see the terrain going up 2000 m before the threshold but the chart ends before the peak is reached. 2000 m before the threshold, the terrain is still below the airport elevation. I guess it is not common to have a relevant feature 3km before the threshold...but on the other hand, I guess it is not common to have a RA of 500' at DH either.


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Old 2nd Sep 2015, 08:56
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ummmm....MA below the DA?
Sorry underfire, I was trying to reply Derfred hypothetical scenario.

My sentence should have read:
"If the missed approach were initiated below the DA the protection in the missed approach would be reduced"

Clearly, that shouldn't be done.

I have edited my reply. Sorry for my mistakes with English grammar.
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Old 2nd Sep 2015, 09:47
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Re Peeka4y's response:
Quote:
Remember that while the LOC MDA is a "hard deck", the ILS has to provide protection even if the aircraft is flown below the glide slope (up to full deflection), and below the DA when a missed approach is initiated.

It's still rather strange that the ILS Cat I DAs for Cat BCD are higher than the LOC Only MDA!
Perhaps if they lopped off the top of some of those trees in the final segment (as shown in the "Southern Germany" lookalike pic) the CRM analysis for determining the minima for the precision approach? Or, perhaps those who designed the approaches only used the OAS (Obstacle Assessment Surfaces) method and didn't do a CRM (Collision Risk Method) analysis, where the latter may in fact give lower DAs that are equally safe.


Re EnxAero's response to Defred:
Quote:
I guess what peekay4 means is that if you started the missed approach at precisely DA, the aircraft still loses a bit of altitude until you it starts to climb, and it goes slightly below DA. Those few ft are taken into account and the aircraft is protected.
Design of Approaches using Vertical Guidance, where the minima is expressed as a DA/DH (and even RA), always takes into account the sink rate factor that's going to occur if the Decision is made to GA AT or ABV the DA/DH (MA not initiated after/BLW).
And so as EnxAero indicated in one reply, in such cases the design provides protection in the missed approach (for normal ops ... ie, not necessarily EO conditions).

Re the Cat II APCH and the relatively unusual large RAs due to the valley in the 1k are prior to the THR - yup, it is a bit special! Especially if the RA at around 1.6NM (3k) is less than the RA at the 0.5NM (1k) mark!
Possibly that's why that Cat II APCH is a special authorisation required (ref chart below) procedure?

Hmmm, interesting diversion.
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