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View Full Version : Need some advise on the CAT II to RWY 26 at EGGW...


Jet Jockey A4
26th Feb 2016, 22:59
We are starting our CAT II operation soon (people in training now) and I Just noticed this week while landing at Luton that the CAT II minimums there are somewhat unusual (see chart).

http://i17.photobucket.com/albums/b79/mlab601/mlab601066/CAT%20II%20RWY%2026%20at%20EGGW_zpscwo4aq4b.jpg

Here are my questions in regards to this approach on RWY 26 at Luton...

I did notice the CAT II warning note (boxed in red) and perhaps that's the reason behind the RA 132' setting but I'm sure some of the folks that have been flying CAT IIs for a while will know the answer especially the ones that fly into Luton often.

Am I correct to assume that we should set the radio altimeter to 132' for this approach because of the uneven terrain just prior to the threshold of this runway which in turn if you were stable on the G/S and at 132' RA you would then be indeed at a DA of 608' and 100' above the runway?

Would some operators use the DA of 608' for a call and not use the radio altimeter in this case because of the uneven terrain?

Thanks for your inputs.

Mikehotel152
27th Feb 2016, 07:06
From Skybrary:-

...because greater precision is required when flying a CAT II or CAT III approach, special attention is given to the terrain in the runway undershoot to enable a radio altimeter to be used. CAT II and CAT III approaches are therefore always flown to a DH with reference to a radio altimeter.

The fact that there is a note warning of quickly rising terrein in the approach path reinforces this advice.

Goldenrivett
27th Feb 2016, 07:33
Hi Jet Jockey A4,
Would some operators use the DA of 608' for a call and not use the radio altimeter in this case because of the uneven terrain?
Mikehotel152 is correct.

If you look at Manchester RW 05L, there are no Cat II limits published (because of uneven terrain under the aircraft at around 100 feet agl).
You can't use a baro altimeter DA (not accurate enough), and you can't read a radio DH as you fly over the river Bollin valley. So you can only do a CAT I or CAT III approach to RW 05L.

Mikehotel152
27th Feb 2016, 09:21
Goldenrivett,

Can you just clarify which bit is correct?

If there are no Cat II limits published for MAN RW 05L then there is no Cat II approach to that runway, probably for the reasons you specify.

However, where there is a Cat II approach, such as at LTN RW 26, notwithstanding the warning about the sloping terrain, surely you cannot fly that approach using a DA?

RAT 5
27th Feb 2016, 09:44
From decades ago at LTN, in B732 (Cat 2 a/c) days, there was no CAT 2 RW26 at LTN. This was due to the terrain in the undershoot. The RA readout was not suitable and at 100' ATHR the RAD ALT was unreliable. CAT 3 was allowed because the a/c was at 50' above the flat (almost) tarmac.
To solve this problem I think they installed RAD ALT reflectors on the approach lights so the readout at 100' ATHR would be accurate. However, approaching the DH point below 1000' (3nm) the RAD ALT readout will be sensible; it will then change from a reducing RA height to a rapidly increasing RA height as you fly over the valley. The RA height will then start to reduce again at an unusual fast rate and can be very confusing.
Seeing this 608'DH = 100ATHR might suggest another solution has been used to the radar reflectors on the approach lights. Perhaps there is now better land surveying of the undershoot. The locals might tell us the uptodate situation. But, most modern a/c that are CAT 2 are usually CAT 3. So they would fly CAT 3 in dodgy weather, if available. There are technical reasons, both airborne & ground equipment, that only CAT is available.
What might be interesting (and I can't remember what we did in B767 days) is the 500' ALERT HT. This is a RA height and a decision about the Land Status. 500' height = 1.5nm on finals. I wonder what the RA readout is at this point? Locals again?

7478ti
27th Feb 2016, 19:41
For US operators,... See FAA AC120-28D. Normally, Alert Height (that is Operational use of AH, ...versus any value potentially considered for aircraft design or certification considerations) is not set above 100' HAT. That's because the higher the alert height, the less conservative the safety application due to the continuation consequence. Conversely, the lower the AH, the safer the application, because the result is a go-around for a mode reversion or failure.

Further, "Irregular terrain" considerations should typically be assessed for each aircraft type and AFDS system used, while in weather conditions better than when Cat II or III minima are actually needed. See also AC120-28D and AC120-29A.

The "caution note" on the EGGW SIAP is most unusual, and would be much better addressed and placed in any ops authorization to use that specific procedure, so as to remove any such interpretation ambiguity. That's why specific "Irregular Terrain" assessments, qualifications, and authorizations are typically used for both autoland (and HUD AIII mode) for various aircraft/system types, and for US based ILS or GLS runways with underlying irregular pre-threshold terrain. Again,... See FAA AC120-28D section 6.2.5, 10.7, and Appendix 8.

172_driver
27th Feb 2016, 20:21
Am I correct to assume that we should set the radio altimeter to 132' for this approach because of the uneven terrain just prior to the threshold of this runway which in turn if you were stable on the G/S and at 132' RA you would then be indeed at a DA of 608' and 100' above the runway?

Short answer: Yes

Jet Jockey A4
27th Feb 2016, 22:14
Thank you to all that answered.

Cheers!

Flap40
1st Mar 2016, 13:47
Just an addition to point out that there is a Cat II approach to 05L at Manchester but it is restricted to Cat A & B aircraft.

The lower approach speed means that rad alt behaviour is acceptable.

http://www.ead.eurocontrol.int/eadbasic/pamslight-B1F398B899066AA6DE8CB18D1BE441C2/7FE5QZZF3FXUS/EN/Charts/AD/NON_AIRAC/EG_AD_2_EGCC_8-5_en_2012-06-28.pdf