EU-OPS 1 AOM for CAT I / NPA question

[arxipov]

Ok, there is that Appendix 1 to OPS 1.430 which explains how to get minimum RVR/CMV for CAT I and non precision approaches provided you have DH/MDH, slope angle and approach lights system length:

Required RVR/visibility (m) = [(DH/MDH (ft) × 0,3048)/tanα] – length of approach lights (m)

And there is that table containing lowest allowable values of RVR/CMV for instrument approaches with vertical profiles up to 3.77° for Cat C/D aircraft and various approach lights systems.

Everything goes perfect when you fly your standard 3° GS / DH 200' / RVR 550 m approach to at least CAT I runway.

But here's the question. Let's assume we're flying RNAV(GNSS) approach to LKPR RW24 using LNAV managed guidance only, and reported RVR is 1200 m.

http://i65.tinypic.com/20z9thu.png

http://i63.tinypic.com/346kv47.jpg

At DH we will be
412 × 0,3048 / tan(3°) = 2396 m from touchdown,
or 2396 - 1020 = 1376 m from the beginning of the ALS...
MINIMUM? GO AROUND, FLAPS!

Ok, second approach, RVR became 2000 m, but approach lights have failed.
At DH we will be 2396 - 300 = 2096 m from threshold.
MINIMUM? GO AROUND, FLAPS!

Where is the trick?
These minimum RVRs are extracted from that table, which was calculated using slope angle 3.77°. You can check it yourself:
For NALS: RVR = (412 × 0,3048)/tan(3.77°) = 1905 m.
For FALS reduce it by ALS length: 1905 - 720 = 1185 m.
And note that these values include approx. 300 m margin, because ALS starts from RW threshold.

But if you fly 3° approach instead of 3.77°, at the same altitude you will be tan(3.77°)/tan(3°) = 1.26 times further away from the runway!

So, three questions:
1. Why is that table applicable for approaches with vertical profile up to 3.77°, and not "down to"?
2. Why is distance from threshold to touchdown not used in minimum RVR calculation?
3. What am I doing wrong? :ugh:

[alphacentauri]

arxipov,

Not specifically familiar with EU ops but and the all the information I am about to provide is from the Australian context.

So far as I am aware, visibility and RVR are not the same thing. The formula you quoted and used, is the standard formula for calculating visibility. We all know that the quoted visibility must be enough for you to see the landing area or start of the lighting system. This is not the same as RVR but you appear to be using the terms interchangeably.

In Australia we only publish RVR's for precision approaches and they are standard depending on the DA. They are not individually calculated for each scenario.

I have no idea if this helps....but I think you are calculating one thing and trying to apply it to something different.

Someone more familiar with EU ops will be along shortly to clarify, but that is my suspicion of your problem.

Alpha

[arxipov]

Alpha, you're right.
RVR/CMV and VIS are not the same thing indeed.
At night we could have 600 m of visibility, which would be equal to RVR/CMV 1200 m provided HIALS and HIRL are operative and RVR is not reported. (EU-OPS again)

But with either RVR 1200 m or VIS 600m we won't be able to see approach lights that are 1376 m away.

We don't calculate minimum RVRs either, as they are standard for given DA(H), but it seems that for 3° profiles and DH > 350 ft that standard minimums could lead to weird results.

[FlightDetent]

Few technicalities, but I promise to have a look at the geometry later too.

a) are you looking at
Amendment 1 to EU-OPS OPS 1.430, or
Amendment 1 (new) to EU-OPS OPS 1.430 ?

The old one is carried over from JAR-OPS, the new has some changes including an increase of required VIS / RVR for NPAs.

b) EU-OPS is dead. Superseded by EASA Air-OPS or EASA-IR. I understand the minima section is however unchanged from EU-OPS Amendment (new) 1 to OPS 1.430. Hence the correct use of Jeppesen minima table with [Standard] on it.

Minima table from Lido:
838
This does not show RVR is required, but that's besides your point.

EDIT: In the meantime, are you able to calculate how much RVR is equivalent to the 1200 m VIS printed on the Lido chart?

[arxipov]

Well, that was from Amendment 1 (new), and according to our OM-A, we're still using EU-OPS.

That's weird as well: we have that [standard] label on a Jeppesen chart, but we need RVR 1200 m for that approach.

And no, we don't calculate RVR that way. If there is VIS minima, or RVR and VIS, or no prefix (your case), we have to use VIS without conversion.
But if we try, that corresponds to at least RVR 1800 m (day), so with VIS 1200 m reported you would see approach lights at DH and land.

In other words, looks like this is a Jeppesen fault?

[FlightDetent]

Numbers are the same, they need to work.

LKPR ALS CAT II is 900 m.
RDH for the approach is 49,2 ft ;)
VPA for the approach is 3,0 deg ergo 5,24 %

For a triangle like yours, the vertical Delta from threshold crossing altitude to DA is
vd = DA - RDH - THR ELEV = 1570 - 49 - 1158 = 363 ft ergo 111 m

The lateral distance required to lose 111 m is 111/0,0524 = 2118 m.

2118 - 900 = 1218 m, close enough for 1200 VIS minima.

[arxipov]

Many thanks, FlightDetent!
Looks nice, but how about NALS (ALS out) case?

[FlightDetent]

:) Well, I think 2118 - 0 = 2118 m. If the visibility is less than 2100 m, you will not see the runway.

Why is Jeppesen showing 1900 I do not know, is this the correct figure as calculated by the Amd 1 (new) OPS 1.430 equation?

On a secondary topic, why they show RVR is also beyond my understanding. The relevance of any RVR measurement in TDZ towards pilot's decision on an NPA - 2 kilometers away and up in the air is, ... er, very distant? :sad: Alphacentrauri provides a good lead on this. Austria or Australia, the aviation rules are pretty much identical, especially those related to geometry and physics. Even if the wording may be different.

[good egg]

Not sure if you're interested or not but I stumbled across this article when proposing changes to Low Visibility Operations at my unit...

http://www.icao.int/safety/meteorology/amofsg/amofsg%20meeting%20material/amofsg.10.sn.011.5.en.pdf

(Sorry, not sure how to post a link from my iPad!)