View Full Version : ILS Catergories
I was studying some approach plates recently when I can across a CATIII ILS plate and a CAT I for the same runway. I was wondering . . . why do they catergorize them exactly?? I understand what they do for catergorization (visibility, etc) but I mean, an ILS is an ILS right? What do CAT 3 ILS's have that CAT I s don't?
dino737
16th Feb 2001, 03:08
Hi,
A CAT3 ILS is indeed the same ILS on the same RWY but the difference are the landing minima.
When Low Visibility procedures are in effect on an airport (when there is mist or low ceiling) the separation between the aircrafts are greater. On the ground the sensitive zone around the RWY in use must also be greater.
So when you do an ILS CAT1 you have to see the RWY at 200ft the latest and when you do an CAT3 you only need 50ft are in some cases you don't have to see the RWY. When you do an CAT3 approach it is also fully automatic and the autopilot lands the aircraft!
A CAT3 is only when it is bad weather!
Hope this is an answer,
DINO
FO B-737
JABBARA
16th Feb 2001, 04:23
Hi!
If an aerodrome is categorized as CAT III, that means the beam quality (both for LOC course and GP) is assured below CAT I DH (that is around 200'RA). To maintain the currency of CAT II/III status of an ILS of a specific runway, the sensivity or the quality of the emmitted electronic signals are periodically checked by airport authorities. Besides this, only if certain terrain feautures are available just next to the approach end of runway, then this runway can be approved and certified for CAT II/III operation. So publishing a seperate chart for these operations may be necessary.
I hope, I could explained my opinion despite my broken English.
Bye.
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Thank you both. You both answered my question. SFly
Gonzo
18th Feb 2001, 03:09
Added to the above, to obtain a CATIII 'rasting', an ILS has to be radiating for a set amount of hours, continuously. I think it's around the 8-10,000 hours mark (?). Interesting for LVPs at Heathrow when we get the ILS replaced this summer on 27R!
Gonzo
airbus wannabe
18th Feb 2001, 14:17
Gonzo, wjat is your status at LHR? While they replace the ILS, where will the planes land...? same runway? if so, that is terribliy dangerous i would expect?
Smooth skies,
Dan :)
Gonzo
19th Feb 2001, 00:34
Airbus Wannabe,
Well, they tell me I'm an air traffic controller, but I'm not so sure of the 'control' bit!!! My status? I wonder that myself sometimes ;) ;) ;)
If I can recall correctly (we recently had a briefing on this). In the next few years, both runways are to be resurfaced. Basically they close one runway overnight, 2300-0600, and do a little bit, then open the runway during the day, then that night they close it again and do the next little bit, etc etc. After so many months, they complete one runway, then go on to the next. As part of this, they are going to replace the ILS systems, which actually takes one day, I think. (it was at this point in the briefing that the food was brought in, so my attention wandered!!!!).
So I anticipate that if this is the case, we'll stop the alternation and land the whole day on the ILS-equipped runway, and depart on the non ILS runway. Or if the Approach guys feel up to it, SRA talkdown approaches to the non-ILS runway in accordance with the alternation programme.
If anyone from LL ATC is around in this forum and was paying attention, maybe they could jump in!?!?!?!?!
Gonzo
[This message has been edited by Gonzo (edited 18 February 2001).]