CAT-II / CAT-III sign

[EHM-1001 Robert]

Hi there,

just a simple question... I never thought about why is it important to place CAT-II or CAT-III signs next to the taxiways. When you reach to a holding point, at many airports there are signs at the runways like "CAT-II RUNWAY AHEAD" and such.

Why is it important to know for a pilot that is only taxiing that which type of runway he is approaching? Why is it important to know it on the ground?

[EHM-1077 Emanuele]

There are probably various characteristics
in which the various taxiway differ from
category to category.

One is definitely the starting position on
the runway they lead you to. I.e. a Cessna
doesn't need 3 Km of runway to take off
as the 747 does.

Additionally, the bigger the plane the
larger his rate of turn is. Some narrow
taxiway with tight turns
might not be suitable for a big bird.

And I bet there are also some weight
considerations.  If the asphalt and the
stuff underneath isn't made to support
a certain load, it will collapse. And the
load of a CAT I is pretty different from
a CAT III plane.

These are a few ideas. There might be
other issues I don't know...

Ciao ciao!

Manu

[EHM-1388 Tiberiu]

No no no...

I did a little research, but information is scarace on the CAT signs.

First of all, CAT I/II/III are categories for ILS approaches:

Category I: aircraft may continue a controlled approach to the runway down to a DH of no less than 200 feet (or 60m) above ground.  Other minima like horizontal visibility and visibility along the length of the runway also apply – at least a half a mile (0.8km) horizontal visibility or a Runway Visual Range of 2600 feet (800m).

Category II: aircraft may continue approaches to the runway down to a DH of 100 feet (30m) above ground, and conditions must allow for a Runway Visual Range (RVR) of only 1200 feet (360m).  Category II minima also requires the certification of the operator, the pilots, the aircraft, and the airport, by the national authority.

Category III: as you may have already guessed, Category III is essential a ‘blind’ approach flown ‘hands-off’ all the way to touchdown. Of course, Category III has even stricter requirements for the operator, pilots, aircraft, and airport. The minima for Category III are a DH of 50 feet (15m) and visibility of 1/8 of a mile (200m).


Now, about the CAT signs. They are actually Hold Short signs, suplementing the hold short line. So, for example, if there is a plane performing a CAT II approach, you should hold short at the CAT II sign. So the ideea is to give more space in accordance with the precision of the ILS category.
I somehow doubt that there are 3 hold short signs at each rwy (approved for all three CATs let's say), there is probably just one CAT II/III like in this picture