CAT II/III landing

[john89]

Hello everybody,

Having recently visited an International Airport, I have got one more question ;-)
Probably you can help me clarify something regarding the CAT II/III marking strips. When there are unfavourable weather conditions like fog, leading to a Category III landing approach, I guess those strips are rendered nearly invisible!?
Is the respective CAT - marking strip possibly illuminated?
Are those markings just an indicator showing that nobody is allowed to cross the respective strip on the taxiway while the landing manoeuvre is being carried out?

To put it in a nutshell: What exactly do those strips indicate and how do you know which one is currently active?

Thanks in advance for your help,
John

[D Ramapriya]

On Aug 12, 1:35*am, john89 > wrote:
> Hello everybody,
>
> Having recently visited an International Airport, I have got one more
> question ;-)
> Probably you can help me clarify something regarding the CAT II/III
> marking strips. When there are unfavourable weather conditions like
> fog, leading to a Category III landing approach, I guess those strips
> are rendered nearly invisible!?
> Is the respective CAT - marking strip possibly illuminated?
> Are those markings just an indicator showing that nobody is allowed to
> cross the respective strip on the taxiway while the landing manoeuvre
> is being carried out?
>
> To put it in a nutshell: What exactly do those strips indicate and how
> do you know which one is currently active?


I'm not sure what strips you're referring to. AFAIK, an ILS has two
systems, both of which are radio-based - the localizer which gives you
a lateral directional reference and the glideslope which is an aid for
vertical descent.

Normally the decision-making height and runway edge visibility for CAT
II are 30 and 300 meters respectively. At CAT III airfields like LHR,
the visibility could be zilch and still land but I've heard that some
operators have their own additional safeguards written into their SOPs
like, say, 15 and 75 m even for CAT III.

Ramapriya

[john89]

"I'm not sure what strips you're referring to. AFAIK, an ILS has two
systems, both of which are radio-based - the localizer which gives you
a lateral directional reference and the glideslope which is an aid for
vertical descent."

Hi

Well I refer to the markings on the taxiway, parallel to the RWY, perpendicular to the TWY, (dashed or dotted lines if I remember correctly), which are supposed to have something to do with CAT II/III approach.
Hope that helps!?

John

[Robert Moore]

john89 wrote
> Are those markings just an indicator showing that nobody is allowed to
> cross the respective strip on the taxiway while the landing manoeuvre
> is being carried out?

YES, an aircraft any closer to the runway centerline might disrupt the
radio beams for landing aircraft.

From the AIM:

k. ILS Course Distortion

1. All pilots should be aware that disturbances to ILS localizer and
glide slope courses may occur when surface vehicles or aircraft are
operated near the localizer or glide slope antennas. Most ILS
installations are subject to signal interference by either surface
vehicles, aircraft or both. ILS CRITICAL AREAS are established near each
localizer and glide slope antenna.

2. ATC issues control instructions to avoid interfering operations
within ILS critical areas at controlled airports during the hours the
Airport Traffic Control Tower (ATCT) is in operation as follows:

(a) Weather Conditions. Less than ceiling 800 feet and/or visibility 2
miles.

(1) Localizer Critical Area. Except for aircraft that land, exit a
runway, depart or miss approach, vehicles and aircraft are not
authorized in or over the critical area when an arriving aircraft is
between the ILS final approach fix and the airport. Additionally, when
the ceiling is less than 200 feet and/or the visibility is RVR 2,000 or
less, vehicle and aircraft operations in or over the area are not
authorized when an arriving aircraft is inside the ILS MM.

(2) Glide Slope Critical Area. Vehicles and aircraft are not authorized
in the area when an arriving aircraft is between the ILS final approach
fix and the airport unless the aircraft has reported the airport in
sight and is circling or side stepping to land on a runway other than
the ILS runway.



b. Holding Position Markings for Instrument Landing System (ILS).
Holding position markings for ILS/MLS critical areas consist of two
yellow solid lines spaced two feet apart connected by pairs of solid
lines spaced ten feet apart extending across the width of the taxiway as
shown. (See FIG 2-3-16.) A sign with an inscription in white on a red
background is installed adjacent to these hold position markings. When
the ILS critical area is being protected, the pilot should stop so no
part of the aircraft extends beyond the holding position marking. When
approaching the holding position marking, a pilot should not cross the
marking without ATC clearance. ILS critical area is not clear until all
parts of the aircraft have crossed the applicable holding position
marking.

[D Ramapriya]

On Aug 12, 10:55*am, john89 > wrote:
>
> Well I refer to the markings on the taxiway, parallel to the RWY,
> perpendicular to the TWY, (dashed or dotted lines if I remember
> correctly), which are supposed to have something to do with CAT II/III
> approach.
> Hope that helps!?


Yep, and I apologize for having gone on about something else
altogether... crikey!

Ramapriya

[Brian Whatcott]

john89 wrote:
> Hello everybody,
>
> Having recently visited an International Airport, I have got one more
> question ;-)
> Probably you can help me clarify something regarding the CAT II/III
> marking strips. When there are unfavourable weather conditions like
> fog, leading to a Category III landing approach, I guess those strips
> are rendered nearly invisible!?
> Is the respective CAT - marking strip possibly illuminated?
> Are those markings just an indicator showing that nobody is allowed to
> cross the respective strip on the taxiway while the landing manoeuvre
> is being carried out?
>
> To put it in a nutshell: What exactly do those strips indicate and how
> do you know which one is currently active?
>
> Thanks in advance for your help,
> John
>
>
>
>
CAT 3 landings are made by suitably equipped aircraft at suitably
equipped airfileds. The requirement is for continued guidance after
touchdown, not out the window....

Brian W

[bobmrg]

On Aug 12, 12:55*am, john89 > wrote:
> "I'm not sure what strips you're referring to. AFAIK, an ILS has two
> systems, both of which are radio-based - the localizer which gives you
> a lateral directional reference and the glideslope which is an aid for
> vertical descent."
>
> Hi
>
> Well I refer to the markings on the taxiway, parallel to the RWY,
> perpendicular to the TWY, (dashed or dotted lines if I remember
> correctly), which are supposed to have something to do with CAT II/III
> approach.
> Hope that helps!?
>
> John
>
> --
> john89

Bob Moore gave you the correct answer...they have nothing to do with
the approach itself.

Bob Gardner

[Gauntlet]

The hold point markings are exactly as have been described above.

When taxiing out to the runway, the pilot would be unaware whether the ILS was currently being used for Cat I or Cat II/III approaches (but they would have a pretty good guess based on the weather!). But you can be sure that ATC would know. Therefore, the taxiing pilot would be cleared to proceed as far as the relevant holding point for the runway. For example, the Cat I hold could be designated "Alpha 1"; the cat II as "Alpha II".