ILS clearance & critical area
 

In my airport ,when aircrafts need to take off with the whole runway ,they need to pass the critial area ,and that will affect the aircrafts approaching on final ,so is it right to give the ILS approach clearance and remind the pilot GS may not be stable if the weather is fine so that the pilot can visual of field or just let the aircraft descend to the minimun safety altitude and give the ILS clearance when aircraft leave the critical area ?

ILS critical area is only important during CATII/III conditions, i.e. low vis.

Glamdring, that's the sensitive area, the ILS critical area is important for all ILS ops.

Cauatc, we have one runway the same as yours, as aircraft line up from the full length, they pass through the glide path critical area. In the past, we would simply warn the aircraft on approach that they may experience fluctuations on the GP, but now we simply do not use that line up route when any aircraft is within 15nm on an ILS approach (protected range on the GP).

Of course, the localiser critical area is harder to protect, and so if an aircraft rolls right to the end of one of our runways, we simply warn all following aircraft of fluctuations on the localiser. The A380 has a larger localiser critical area due to its size, and will infringe its critical area if it rolls to the end on any of our runways.

Yeah, I stand corrected. It's early ;)

Gonzo
Thanks for your information ,I am an ATC in BeiJing ,China ,we have three runways ,we only have that problem for the middle runway ,what we do rencently is do not let the aircraft get into the critical area if there is an aircraft on the 40Km (about 15NM )to touch down and try to let the pilot get visual contact with airport if weather is good .
Thanks for your help again.:ok:

Just got a question ,can I say the GS is normal just at the moment the aircraft leave the sensitive area ? Is there a time requirement for that ?

There seems to be a lot of confusion here between the "critcal area" and the "sensitive area".
The critical area remains the same for all aircraft.
The size of the sensitive area is dependant on the size of the aircraft within it.
I would find it difficult to believe that any airport regulator would permit aircraft movements through the critical area while that system was radiating.

westham,

Don't think anyone's confused.......:confused:

The Localiser critical area we have is 1000m in front of the localiser antenna for the A380, which extands on to the upwind end of every runway, rather than the smaller localiser critical area for Code E a/c which is, off the top of my head, 660m, which only infringes the upwind end of one of our runways.

The GP critical area we have an issue with (27L, line ups via SB1) is now, as I said above, a no-go area when a/c are within the protected range of the GP, which is 15nm. It used to be the practice to warn of fluctuations and keep going if it was a nice visual day. Our GP critical areas are the same dimensions regardless of a/c type, but not or Localiser Critical areas.

Gonzo, you are still talking about the sensitive area, not the critical area.
The localiser critical area is equipment specific, but is nominally 300m in length and 120m in width.
The localiser sensitive area is dependent on the ILS category (I/II/III) the number of elements in the localiser antenna and the obstruction within the sensitive area. For a B747 in the sensitive area of a 14 element antenna on a Cat III system, the sensitive area stretches 2750m from the centre of the localiser antenna.
These figures are from ICAO Annex 10 vol 1.

All due respect westham, I'm not. I have no knowledgde of such areas outside of Heathrow, but we use the Code E LLZ critical area of 660m in length, and 60m from the runway centreline for all a/c, apart from A380 which is 1000m long, the additional length of 340m being extended to 90m from the runway centreline. The GP critical area for 27L extends across the taxiway leading on to the runway from holding point SB1.

In CAT II/III ops the Localiser Sensitive Area we use for all aircraft is 137m from the runway centreline, apart from when an A380 is on the ground and moving when we use the Code F dynamic LSA which varies from 160m (second half of runway) half of runway to 192m (first half) from the runway centreline, apart from the first and last 200m of the runway when it's 137m.

The GP sensitive area is far larger than the GP critical area, and this affects both 27L and 09R line-ups from the south. 27L has CAT II/III holds on the south at the full length, but 09R does not.

All those figures are from memory, so they might not be completely accurate!

I believe in JAA that the ILS critical area protects the ils under normal conditions and the ils sensitve area under cat II/III.
I also believe that the FAA call it LLZ/GP critical area for normal ils and ils critical area for cat II/III.

Maybe that is where the confusion lies.

Gonzo, the ICAO definition of a critical area is:
The ILS critical area is an area of defined dimensions about the localizer and glide path antennas where vehicles,
including aircraft, are excluded during all ILS operations. The critical area is protected because the presence of
vehicles and/or aircraft inside its boundaries will cause unacceptable disturbance to the ILS signal-in-space
The ICAO definition of a sensitive area is:
The ILS sensitive area is an area extending beyond the critical area where the parking and/or movement of vehicles,
including aircraft, is controlled to prevent the possibility of unacceptable interference to the ILS signal during ILS
operations. The sensitive area is protected against interference caused by large moving objects outside the critical
area but still normally within the airfield boundary.
As per the definition, if aircraft are in this area, it cannot be a critical area

I agree with and understand those definitions. No issue with that, and consistent with our ops. If an A380 rolls into the enlarged LLZ critical area then our procedures say that the ILS is not to be used until it vacates.

Hello

westham

Quote:

---

The ILS critical area is an area of defined dimensions about the localizer and glide path antennas where vehicles, including aircraft, are excluded during all ILS operations. The critical area is protected because the presence of vehicles and/or aircraft inside its boundaries will cause unacceptable disturbance to the ILS signal-in-space

---

my emphasis

The definition doesn't say that at all really. It states that vehicles and aircraft can't be within the critical area if there is an aircraft making an ILS approach. Just because there is a vehicle/aircraft in the critical area it doesn't cease to exist. Notice how the definition states the critical area is protected and not prohibited.

Therefore as Gonzo said aircraft can transit / sit in the critical area as long as there isn't an aircraft using the associated aid, the GP in LHRs case.

Similarly you could have an aircraft / vehicle sat in the GP critical area as long as the approaching aircraft wasn't making a GP assisted approach, i.e. LOC/DME, RNAV, MLS, Visual, etc.

help?
 

Who can draw me a detail graph indicating the demension requirement on ILS critical and sensitive areas?

hyzhao11
I have had "google" the "critical area" and did find one , I will try to find if I can still find that ,by the way ,are you BeiJing ATC also???

Annex 10 Vol 1 diagram
 

hyzhao11 & caucatc,

Track down a copy of ICAO Annex 10 Vol 1. (current amendment is 84). There are example diagrams in Attachment C pages 9, 10 & 11 that show the LLZ & GP dimensions for critical and sensitive areas.

For other antenna types you need to speak with the equipment manufacturer to get the correct figures.

As has been stated above, the size of the aircraft operating at a particular airfield is only one factor in determining the dimensions of the areas.

You also need to consider the technical safeguarding of the LLZ and GP sites, which involves thinking about the effects that buildings, fences and other metal structures can have on the beam formation for ILS systems. Trees (foliage, and whether wet or dry) can also have an effect as can the water table under the surface. All of these need to be considered when planning for an ILS installation. If, after an ILS enters service, there are unexpected alarm conditions, all of the above need to be re-examined to see if "something has changed" in the environment near an ILS installation.

For one set of criteria for Technical Safeguarding have a look at CAP 670 (available here: http://www.caa.co.uk/docs/33/CAP670.PDF) section GEN02.

Hope that helps.

Regards

ST