ILS

[Aviation Freak]

-What does it stand for?
-Is there a certain range you need to be at to intercept?
-How does it work?

Thanks!

[Zaffex]

I'll give a shot at this, please correct me anyone if I'm wrong. ILS stands for Instrument Landing System, and is used to guide aircraft to the runway in bad weather conditions (IFR). Basically it sends out a signal that you tune the aircraft radio to, then you follow the system almost to the runway. Once you can see the runway, you land the plane. That's my "rough cut" on ILS. You can probably get a better description from people who've actually used it in real life, and many of these guys sound very willing to help you out with any info they have.

[Ted_Stryker]

Good brief on it, Zaffex!  You are correct in how it works.

There are many components to the ILS system in total.  There is various forms of runway and approach lighting, different kinds of ILS "approaches" which use different kinds of radio navigation tools, and different kinds of procedures to handle different kinds of "approaches" too.

The approach is also only one area of Instrument flight.  There are "SID"s too.  An instrument "approach" is called a "STAR", which means Standard Terminal ARrival procedure.  A "SID" is a Standard Instrument Departure procedure.  It would literally fill a book on how all this stuff works, and now with GPS and WAAS coming into the picture the ILS systems are changing, and becoming available at airports not formally equipped with what has traditionally been known as an "ILS".

When someone is referring to an ILS generically, they are generally referring to what is known as a "localizer" in conjunction with an on-airport "VOR"  The VOR portion provides left-to-right guidance, while the "localizer" provides the vertical slope, or glide slope, information.  So, when you are on a full "ILS" approach, you are really using two different radio signals to guide you down.  There are other ways for finding the airport too.  There are Ground Surviellance Radar approaches (widely used by the military in conjunction with a "GNC" officer), NDB approaches, which use the ADF radio (these are going away), and GPS now too.  As I said... there are plenty of things I could write about here to explain all of it, but I'm not a CFI, and it would take a book, literally, to deal with the topic.

The thing to also know is that the ILS system is a term generally used to denote the entire range of Instrument approach and departure procedures colloquially, while flying an actual "ILS" is dealing with the two different, high precision, radio beams providing horizontal, and vertical navigation information.  Oh, and yes, you can have an "ILS" that does not provide glide-slope information.  In cases like that, the procedure is to use speed, and time from known points to plan decent rates so you end up where you are supposed to be.

Ok... I suspect this has totally confused many at this point... so I'll stop here.   

[Ted_Stryker]

I also forgot to address your ranging question.  Different ranges apply to various points in the system and the types of equipment being used.  There are three "phases" of Instrument flight.  Departure, Enroute, and Approach.  Each has a very specific procedure for various things with both routing, and handling of radios, etc.  Each approach to an airport has something called an IAF, which means "Initial Approach Fix".  This is where the actual approach to an airport starts.  It can have various ranges and procedures.  The thing to remember is that an approach is the final portion of an Instrument flight, and that the "STAR" (Standard Terminal ARrival procedure) handles the closer proximity to the airport and contains the descent information.  Normally approaches are within 10 to 15 NM of the arrival airport... but this is not necessarily written in stone.

For that matter, procedures don't remain static once they are defined.  They can get changed any time it is required.  This can happen because of a new building, radio tower, or other change in clearances from obstacles, or even noise abatement, is required.  Every 56 days new issues of these "SIDS", "STARS", and enroute maps get updated.  Between updates, there are also publications of updates too, and the pilot needs to really check carefully if a procedure has changed prior to leaving on any given flight for maximum safety.

I hope all this is of help, and hasn't confused things horribly for you.

[wbarnhill]

There are Ground Surviellance Radar approaches (widely used by the military in conjunction with a "GNC" officer)

One of the most fun things I did during training was an ASR (Airport Surveillance Radar) landing at GSP.  Under the hood with instructions every 30 seconds or so, when they finally said "You're 1/2 mile from threshold, on heading, 1000 ft, cleared for touch and go."  Instructor had me remove the hood and it was just beautiful.  It's definitely an experience and a great resource if you ever get caught in instrument conditions unwillingly   And from what I understand the tower guys have to have or practice an ASR approach every 90 days.  So it's a good idea if any of the airports in your area have radar capability to give it a shot

[Gulfstream Driver]

Very well explained, everyone.  One small point...The localizer gives left/right indications, the glideslope gives up/down.  Basicly, if the glideslope goes out, you can still get to the airport with a localizer approach. 

ASR's are a lot of fun.  You get your own frequency and everything.      Wbarnhill's right, controllers do need to practice them, so whenever you get a chance, ask for one.  If I remember right, the airport needs to have RADAR on the field in order to have an ASR.

[Ted_Stryker]

Very well explained, everyone.  One small point...The localizer gives left/right indications, the glideslope gives up/down.  Basicly, if the glideslope goes out, you can still get to the airport with a localizer approach. 

ASR's are a lot of fun.  You get your own frequency and everything.      Wbarnhill's right, controllers do need to practice them, so whenever you get a chance, ask for one.  If I remember right, the airport needs to have RADAR on the field in order to have an ASR.

Thanks for clarifying that... I realize I mistated that in my earlier post.  That's what I get for thinking faster than typing 

[Ted_Stryker]

One other thing you may want to use to help you out is getting a copy of the AIM (Airman's Information Manual).  It tells you how everything works in detail, though it's designed as a reference, not an instructional text.  If you want to know more about instrument flying, the FAA puts out a book on that too, but I'd recommend holding off on that until you have at least primary training done so it makes more sense to you.

ASA Publications puts out a combined FAR/AIM text each year (FAR = Federal Air Regulations), and it's less expensive to buy it that way, than buying the two books separately.  You can even subscribe to email updates through their website to keep up to date with changes between publication cycles.

Here is a link to the ASA FAR/AIM at Sporty's Pilot Shop website.  They have the best price going, even with shipping.

http://www.sportys.com/acb/showdetl.cfm?&catid=180&DID=19&Product_ID=7178

[Gulfstream Driver]

I like ASA's version of the regs a lot better than Jepp's.  It's cheaper and has more information.  ASA's Instrument Flying manual is also a good reference, but I still like the Jepp manuals for private and commercial. 

[Aviation Freak]

Thanks for the help!   I learned a few more things today about something I knew little about.  I like to think of ILS as an Interestin Landing System because every time I try it on X-Plane, I always end up flying aroundin circles.  Also that the system its self is actually interesting to me.

[Gulfstream Driver]

When you're flying an ILS, you want to make sure that your heading is relatively close to your landing runway diretion (e.g. Runway 36, you want your heading to be around 360^o.  Then, just keep the localizer and glideslope crossed in the center, and you'll hit the runway eventually.   

[Aviation Freak]

I did an ILS approach on X-Plane yesterday with a help of a Air Trafic Controler and I mannaged a good landing.
Here is my next related question for this: Is there a point where you disengage everything (VOR Locolizer and APP and other engaged Auto Pilots?

[Gulfstream Driver]

200 ft.

[Bustnthru]

HA its 300 here (nz) stupid backwards tiny country......

[fireflyr]

300 ft--why is that-extreme terrain perhaps?