View Full Version : ILS downgraded to CAT3

Artie Fufkin
16th Mar 2008, 09:37
Amseterdam regularly NOTAM their ILSs on various runways as "downgraded to CAT3".

What is it dowgraded from?

16th Mar 2008, 10:03

I think it was CAT 3 A/B before.

16th Mar 2008, 12:05
Aye down to CAT3 A.

My favourite notam (yes I do have one and yes I am sad) is the one at AMS detailing the "migrating geese" that have been crossing the airfield "between 500ft-700ft". As long as they are cleared through at 600ft, thats CPL standard migration!:cool:

16th Mar 2008, 12:28
From the ground equipment perspective, an ILS either supports CAT 3 or it doesn't. The distinction between CAT 3 A, B or C is operational and is based on aircraft and crew capability, facilitating different decision points.

I agree with Artie, downgraded from what?

16th Mar 2008, 12:41
Hmm. I'm going to AMS later. I'll ask!

Tot Ziens

16th Mar 2008, 12:44
Yeah, I saw that one too! made me laugh...
Maybe they were CAT IV before

16th Mar 2008, 14:14
The full capability of Cat III is Cat III E4.
Anything less is a downgraded situation.

Full capability means that, if aircraft is certified and fully serviceable and crew is certified and authorized, Cat III b without Decision Height is possible with RVR of 75 m.

A downgrade to Cat III E3 or Cat III D4 could impose limits such as minimum RVR 125, or 200 m, or Decision Height 15 ft, or 25 ft, or Cat 3 a, DH 50 ft and RVR 200 m. You would have to check your operational manuals for details.

Artie Fufkin
16th Mar 2008, 14:26
Thanks EMIT, "E3" and "D4" classification of CAT 3 is entirely new to me. Could you point me in the direction of some reading on this?

16th Mar 2008, 19:19
Sorry, at the moment I am enroute for a couple of days and I don't have the books with me.

I do know we have, in our OM (operations manual) a table spelling out the consequences of e.g. III E3 downgrading.
A couple of years ago we had a bit more extensive info about it, but in the drive to more simplification this info was skipped from our books.

Basically the suffixes indicate to what point along the centerline of the runway, what the integrity of the localizer signal is. (1 being low integrity, 4 high, T is 'till touchdown point, D and E closer to the stop end of the runway, if I recall correctly). I think that the philosofy of NOTAM writing has gone more in the direction of stating the result. Cat 1 T3 for instance could mean " no autoland allowed" / better option is to state that restriction, rather than to notify airmen of the T3 status and let them sort it out in their own books.