alisahinler
Topic Author
Posts: 9
Joined: Fri Dec 16, 2016 5:44 pm

AOM-RVR-Ceiling Question

Tue Feb 06, 2018 8:49 pm

Hello everyone, i have couple questions there,

1. AS far as i know in a precision app: RVR is the limiting factor, (visibility or ceiling are not limiting, unless the chart states otherwise)
In a nonprecision approach. Rvr/visibility & ceiling is limiting factors. Is this right? I read on web that people saying, if chart doesn't state that ceiling is a limiting factor than it is not.

2. I saw a nonprecision approach charts with 2800 m RVR minimum.
My question is: If the RVR value is higher than 1500m, rvr's are not published in METAR's. And the chart says RVR, not CMV, so i can't convert visibility to RVR. So why jeppesen charts are published with RVR minimums? Why aren't they just visibility limit??? According to the bottom post, i understand that, in case of no Rvr published, visibility is accepted as rvr. So why not just write there visibility? It is obvious that above 1500m rvr wont be published????

Thanks.

11. DEPICTION OF EASA AIR
OPS AOM IN CASE OF EXISTING
STATE MINIMUMS
If State minimums are officially published, the depiction
of AOM may differ from the standard depiction
where all values are expressed as RVR or VIS.
a. If RVR and VIS are charted together, the RVR
value is compulsory. If no RVR is reported, the
reported VIS has to be used without conversion.
b. No prefix is charted if RVR and VIS is identical.
The reported RVR is compulsory. If no RVR is
reported, the reported VIS has to be used without
conversion.
c. If only VIS is charted, the reported VIS has to be
used without conversion.
d. If CMV is charted, the pilot converts a reported
VIS and compare this value against the charted
CMV.
 
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zeke
Posts: 12348
Joined: Thu Dec 14, 2006 1:42 pm

Re: AOM-RVR-Ceiling Question

Wed Feb 07, 2018 5:31 am

It would be very easy for me to spoon feed you the answer to that, looking at the question you have asked I think you have missed a simple association which unlocks this all.

Instead of complicating the question between precision and non precision approaches, can I ask you why some airports with an ILS are CAT I and others are CAT II/III ?

What could cause a CAT II ILS revert to CAT I (not aircraft, transmitter or standby power related) ?

The answers to those questions will answer why some NPA have published RVRs, think about the V.
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alisahinler
Topic Author
Posts: 9
Joined: Fri Dec 16, 2016 5:44 pm

Re: AOM-RVR-Ceiling Question

Wed Feb 07, 2018 11:30 am

Forgive my ignorance but i can't see the relation between catII/I with my question.
I would appreciate you go a little bit in details thanks.
 
User avatar
zeke
Posts: 12348
Joined: Thu Dec 14, 2006 1:42 pm

Re: AOM-RVR-Ceiling Question

Wed Feb 07, 2018 11:51 am

Will give you another hint, what are the CAT I/II differences here

https://www.icao.int/APAC/Meetings/2015 ... SYSTEM.pdf
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Nicoeddf
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Re: AOM-RVR-Ceiling Question

Wed Feb 07, 2018 12:55 pm

Is it as easy as the differences in the Approach Lighting System which prescribes RVR for NPA vs. VIS?
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User avatar
zeke
Posts: 12348
Joined: Thu Dec 14, 2006 1:42 pm

Re: AOM-RVR-Ceiling Question

Wed Feb 07, 2018 4:53 pm

Nicoeddf wrote:
Is it as easy as the differences in the Approach Lighting System which prescribes RVR for NPA vs. VIS?


Close, one cannot descend below the MDH unless elements of the approach lights, threshold or touchdown zone, markings or lights, or the visual glide slope. Runways that have precision approaches normally always have approach lights that extend from the runway out up to around 900m.

ICAO charts do not actually publish the visibility required on their charts, they display the OCA/OCH. The chart suppliers make it easy for pilots and convert this OCA/OCH into a useful MDA/DH/RVR/Visibility. I will run an example of how they do this.

To calculate visibility EU regulations AMC5 CAT.OP.MPA.110 Aerodrome operating minima DETERMINATION OF RVR/CMV/VIS MINIMA FOR NPA, APV, CAT I — AEROPLANES
(https://www.easa.europa.eu/system/files ... 202017.pdf ) provides the following formula

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

For this example I will use the RNAV 04 at EGSS (London Stansted)

ICAO chart
http://www.ead.eurocontrol.int/eadbasic ... -09-15.pdf

London Stansted Aerodrome - Textual Data
http://www.ead.eurocontrol.int/eadbasic ... -01-04.pdf
EGSS AD 2.14 APPROACH AND RUNWAY LIGHTING
RW04 780m of approach lights

From the chart we can gather the following information, descent path is 3 degrees (5.24%), the OCA is 650', OCH 318', therefore threshold is 332' (same as Jeppesen chart).

If the OCH is 318' (96.93m), and the approach is 3 degrees/5.24%, the triangle for this to hit the end of the runway is 96.93/(5.24/100)=1849m, so if we were to touchdown on the end of the runway we would need to have a visibility of 1849m.

However we do not land at the end of the runway, we cross the end of the runway at the TCH, which for this runway is 53' touchdown point is 1011'/308.29m from the threshold. That means at the OCH we are only 1849-308m from the runway threshold which is 1541m.

The approach lights extend 780 m from the threshold 04, 1541-780=761m, which is rounded down to the Jeppesen RVR of 750m.

Now if we look at table 5 on page 67 of the EU regulation https://www.easa.europa.eu/system/files ... 202017.pdf

For a DH of 318, with the FALS out the NALS RVR is 1400m (1541-210 (maximum)=1331), Jeppesen RVR ALS out 1400m.
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