ILS critical area

Rosstafari Daaaang. /X

Could someone explain what the ILS critical area marks? I have a general idea, but I'm not entirely sure and would appreciate somebody explaining its purpose to me.

Thanks.

SoCal Rookie San Diego

When it was explained to me, years ago, what I understand is that it is the area designated around the ILS antenna which is sensative to objects, personnel, and vehicles entering into and disrupting the signal.

Found this on WIKI:
In aviation, a critical area refers to a designated area of an airport that all aircraft must remain clear of when another aircraft is inbound on an ILS approach. The critical area should be avoided when the weather is less than or equal to 2 miles visibility or less than or equal to 800 ft. ceilings. These areas are used to protect against signal interference that may lead to navigational errors, or worse.

ILS technology delivers two main types of information to pilots. These types include the glideslope (vertical location relative to the designed glide path) and the localizer (lateral position relative to the designed approach course). Each type of information is broadcast using a separate antenna array and each type has a specific critical area.




Localizer critical area - Vehices and aircraft are not authorized in or over the critical are when an arriving aircraft is between the ILS final approach fix and the airport.

Glideslope critical area - Vehices and aircraft are not authorized in or over the critical are 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 sidestepping to land on a runway other than the ILS runway.

For practical purposes, these two area are combined into the ILS critical area and identified by signs and pavement markings.

Roddy_Piper Resident Knucklehead Vegas baby

the area in front of the signal for both the localizer and glide slope need to be protected. that's because a vehicle, airplane, etc could affect the integrity of the signal being broadcast. that's not good. it's a precision approach, so any integrity issues could be a major safety of flight issue.

u only need to protect it inside the OM (or fix used in lieu of the OM) when the weather is less than 800 or 2. u also protect the area regardless of the weather if an aircraft is doing a Cat III ILS, autoland, or coupled approach.

that's all i remember off the top of my head.

polo708 Epic Member tower

thats about it... you are basically keeping planes and vehicles outside of a "critical zone" to ensure no signal interference.

Rosstafari Daaaang. /X

Ahhh. Okay, that makes a lot more sense. I didn't realize that it primarily had to do with signal interference and was under the impression that it was intended to give ILS aircraft more maneuvering room in certain areas... although that didn't really make sense to me.

Thanks for the answers, all.

EDIT: So, assuming the WX is such that the ILS markers need to be observed, would crossing into one without clearance by ATC be considered an incursion? Or just a case of a plane/vehicle not being where it's supposed to?

Roddy_Piper Resident Knucklehead Vegas baby

depends on the airfield layout. at the airport i'm at right now, there is no way to get into the critical area without first getting an ATC clearance into the movement area and thus getting into the critical area. it's up to ATC to know the weather and issue an instruction to keep a vehicle out of the area. it's not the vehicle operators responsibility to know the official weather and when u have an aircraft inside the OM.

at a different airport i worked at the ILS critical area was surrounded by non-movement area. so even in bad weather a vehicle could get into the ILS critical area. so at that airport we were required to notify airport management when the weather went bad. then it was up to them to notify all the vehicle operators to remain outside the ILS critical area.

so, it does kinda depend on the airport your at and the layout of the airfield, where the critical area was in relation to movement/non-movement areas, etc. normally it's up to ATC to ensure the critical area is sterile. the crazy part is that when the critical area is NOT protected (AND bad weather) then all u do is tell the aircraft about it. something like "ILS critical area not protected".

Windsor Newcomer mke/msp

Not quite sure what you mean by "protect it", but what I'm thinking you meant was keep the area sterile or not have any aircraft or vehicles past the ILS hold short line while an aircraft is on the approach inside the OM.

Practice approaches for Cat II & III will also need the ILS area open. If a vehicle or aircraft gets in the way, we (pilots) have to write the approach up as Unsat.

Roddy_Piper Resident Knucklehead Vegas baby

that is correct. no vehicles/airplanes/etc inside the ILS critical area when an aircraft is within the OM (or fix used in lieu of the OM) and the criteria is met.

our regulations don't call for a Cat II ILS to be protected. just a Cat III, autoland, or coupled approach regardless of weather. when the weather is below ceiling 800 and/or visibility below 2 miles then you protect ALL ILS approaches.

Here's what our regulation says:

Windsor Newcomer mke/msp

Coupled is Cat II as well. When I tell approach we are doing a "coupled approach" that means we are doing a Cat II. (My airline is only certified to Cat II mins)

Coupled means we will be keeping the aircraft autopilot on and coupled to the flight director which is recieving input from the loc and gs. For Cat II ops, we will be using the AP all the way down to 80ft above the runway.

Roddy_Piper Resident Knucklehead Vegas baby

so are you saying that "coupled" is ALWAYS a Cat II ILS? a Cat II ILS describes the ILS equipment, not whatever is going on in the cockpit. Is this correct?

that's odd, cuz I've worked at a place that had a Cat II ILS system, but we didn't protect it unless we had 800 and 2. we did not consider the Cat II alone to be considered the same as a coupled approach. ONLY when the pilot tells us they are specifically doing a coupled approach did we protect it.

i guess what i'm saying is that anytime the pilot tells us their shooting a coupled approach, or an autoland approach, or anywhere that might possibly have a cat III ILS. just because yesterday someone shot a coupled approach with a Cat II...does not make that Cat II a permanent coupled approach ILS.