CAT I Approach question

[Inverted7]

Gday,

Got a question regarding CAT I approach in Australia or any ICAO country for that matter, any help would be greatly appreciated!

If the RVR was right on the minima on a CAT I approach, what would you expect to see?


How far can you continue the approach without seeing the threshold?


at what height would you expect to see the threshold if RVR was 550m?

Thanks again for the help.

[OhNoCB]

On a 3 degree glideslope, at a normal CAT1 DH of 200' you will be a touch over 1km from the threshold. Obviously in 550m vis this is not sufficient to see the threshold, but (talking European here I might add at this point) FALS should be at least 720m so you will see the approach lights to continue.

To answer the question at what height will you see the threshold, well some very rough calculations would suggest to me approx 95'.

[de facto]

GDAY to uou too maty,

With 550 RVR you ll see the approach lights of your precision approach lighting system at about 200 HAT.
At about 100 HAT,you will see the threshold unless its covered by snow

If you wanna know more search this and download it: ROYAL AERONAUTICAL SOCIETY FLIGHT OPERATIONS GROUP SPECIALIST DOCUMENT
THE ALL WEATHER OPERATIONS GUIDE CONVERSION COURSE TRAINING MODULE

Enjoy the reading

[Inverted7]

Thanks alot boys, much appreciated!

[Inverted7]

One more thing, so is the vis requirement of a CAT I the same as a CAT II then in which you just need to see three longitudinal lights and one lateral at the minima in order to continue? Thanks again guys, the helps appreciated.

[OhNoCB]

To be honest I have no idea how many lights are required. Our ops manual (bearing in mind CAT I only) leaves it fairly open with wording along the lines of "At DA the pilot must have adequate sight of the landing environment (including the ALS) to execute a normal landing."

[de facto]

Cat1:any portion of lighting system and or threshold
Cat 2/3A: at least 3 consecutives lights and lateral light

[safetypee]

The diagrams below are taken from Cat 2 /3 research documents and show the first contact height and visual segment for a range of RVRs against altitude (m) - Calvert lighting pattern - centreline and 5 crossbars
The first contact height is at the intersection of fog ‘RVR’ line and cockpit cut-off, i.e. 60M/200ft altitude for '600m' RVR.
The visual segment for a particular aircraft type (cockpit cut-off) at lower altitudes, is the horizontal distance from cockpit cut-off line to the fog line, i.e. at 150 ft in 400m RVR, the far point is 255m and near point is 110m; vis seg 255-110=145m. The crew would see the centreline and crossbar 2.
The threshold would be seen at an altitude of 35m / 110ft for the '600m' fog, and just below 100ft in the '400m' fog

For differing fog types/cloud conditions, the lines of RVR will has a different line shape and path.
In the 600m fog shown, the first contact and ‘immediate’ visual segment (just below 200ft) would contain the centreline and crossbar 4. Just enough for Cat 1?



Cat 1 is generally associated with cloud breaks thus a large visual segment would be expected; however in fog, the conditions can have significant variations.
In a shallow fog (13), the threshold might be seen at 200 ft even in an RVR of 300m; hence a min RVR / approach ban.



In more mature fogs (8), nothing will be seen at 200ft (DH), even though the RVR is 600m.

[de facto]

The question is Mr Safety not to say the rest: is 'mature fog' 'heavy fog'?

Interesting diagrams,thanks

[Inverted7]

Thanks very much gentleman. The help is much appreciated! Those graphs are awesome.

[safetypee]

de f, if only we could answer all of the questions in aviation!

For info, the lower RVRs associated with Cat 3 more often represent stable conditions – dense maybe, thus ‘heavy’!!! Having made a decision the visual segment is unlikely to reduce – an opening sequence (type 1 in the lower diagram).

Cat 2 RVRs are more problematical as they are often associated with fog formation or dispersal and other forms of visibility reduction, and with wind. In these circumstances (similarly in Cat 1 pushing the minima), having make a land decision the visual segment could reduce such that a manual landing would be imprudent – a closing sequence (type 13 in the middle diagram).

[chevvron]

'Required visual reference' used to be one crossbar and at least 3 centreline lights of the HI ALS but that may have changed.

[Piltdown Man]

With standard lighting I would expect to see at least six lights and a lateral element. I've normally seen more. At that point you can decide to continue. Providing you see an increasing number of lights and an increasing lateral reference you continue to land. As a previous poster mentioned, an even 550M visibility normally means you'll see the threshold lights around 100' or so.

PM