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How Do You Aim A Localizer Antenna?  
User currently offlineTimz From United States of America, joined Sep 1999, 6816 posts, RR: 7
Posted (7 years 2 months 2 weeks 5 days 17 hours ago) and read 8459 times:

You're installing a new localizer antenna off the end of a runway ... I assume it's midpoint is on the runway centerline and the antenna is supposed to be perpendicular, but probably it does take some slight adjustment? So does someone stand on the centerline at the other end of the runway, with a receiver showing when he's centered in the beam? How precise would such a receiver be at that distance-- how accurately can it pin down the center of the beam?

How do you adjust the antenna-- physically rotate it, or electronically?

10 replies: All unread, jump to last
 
User currently offlineBoeingFixer From Canada, joined Jul 2005, 530 posts, RR: 0
Reply 1, posted (7 years 2 months 2 weeks 5 days 16 hours ago) and read 8448 times:

Localizer antennas are located at the far end of the approach runway. Precise surveying of the site prior to antenna installation is done. Also a magnetic survey of the area is carried out to ensure accuracy of the system. The system can be adjusted in small increments (mechanically) as required to obtain accuracy. All ILS systems, at least in Canada, are subject to verification by suitably equipped aircraft that can measure the accuracy of the system and this is done periodically to ensure the ILS is operating within limits.

Cheers,

John



Cheers, John YYC
User currently offlineBond007 From United States of America, joined Mar 2005, 5408 posts, RR: 8
Reply 2, posted (7 years 2 months 2 weeks 5 days 7 hours ago) and read 8368 times:

Quoting BoeingFixer (Reply 1):
All ILS systems, at least in Canada, are subject to verification by suitably equipped aircraft that can measure the accuracy of the system and this is done periodically to ensure the ILS is operating within limits.

In the USA this is performed by the FAA 'Flightcheck' aircraft, that do multiple ILS approaches and analyze the data.

Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineCorey07850 From United States of America, joined Feb 2004, 2527 posts, RR: 5
Reply 3, posted (7 years 2 months 2 weeks 4 days 23 hours ago) and read 8314 times:

To be honest, unless you've got a degree in physics and radiowaves you wouldn't understand how it's done (don't worry I don't know either)... I can tell you a little bit from my experience though. As you said, the localizer array is usually centered on the midpoint of the runway (most of the time, there are exceptions) and is made up of multiple towers. The cables are fed undergrond and into a small shack (usually referred to as the ILS Shack). Inside the shack you'll find a few large units that resemble something like a computer mainframe. This is where the adjustments take place. To see how much a localizer or glideslipe need adjusting a couple surveys are done. The one that most people see are the flight-check aircraft (usually registered as N1-N99 and are usually King-Air's or Lears). The aircraft will make several approaches to the runway with different on board computers measuring the signal and recording the results. The other survey you see is ground based where the FAA will survey points on the airfield that are at 10, 20, and 30 degrees off centerline from the localizer. These points are surveying using traditional survey methods, and when the FAA comes they basically place their instrument at these points of where the localizer 'should' be and compare the difference.

If the localizer or GS needs adjusting a tech will make the adjustments on the towers inside the ILS shack and is basically altering the frequency eminated from each tower to balance everything and bring it into tolerance. Like I said, unless you have a background in physics it's hard to understand the details of everything (the FAA-AF inspector I deal with has been with the agency for something like 10 years and they were just letting him get into ILS systems).

But to answer your question simply: the localizer is physically mounted exactly how it should, then any adjustments are made electronically by altering the radiowaves.


User currently offlineMD11Engineer From Germany, joined Oct 2003, 13987 posts, RR: 62
Reply 4, posted (7 years 2 months 2 weeks 4 days 18 hours ago) and read 8266 times:

The way the German aviation authorities check ILS systems is by using a converted Beech King Air, which has a precisely calibrated ILS receiver on board. The pilot flies an ILS approach to almost touch down. On the bottom of the aircraft there is a laser reflector. Prior to the flights, a specialist with a laser transit will take position either on the centerline (for localiser) or just beside the touch down zone (for glidepath). The automatic laser trtansit will show any deviations from the theoretical track and the ILD system will be adjusted accordingly.

Jan


User currently offlineBoeing7E7 From , joined Dec 1969, posts, RR:
Reply 5, posted (7 years 2 months 2 weeks 9 hours ago) and read 8086 times:

Quoting Corey07850 (Reply 3):
To be honest, unless you've got a degree in physics and radiowaves you wouldn't understand how it's done (don't worry I don't know either)...

No kidding. In a nutshell, they measure the propagation error and alter the gain to ensure lateral tolerance. Outside of that it's FM (F'ing Magic).


User currently offlineTornado82 From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 2 months 2 weeks 8 hours ago) and read 8077 times:

Quoting Corey07850 (Reply 3):
The one that most people see are the flight-check aircraft (usually registered as N1-N99 and are usually King-Air's or Lears).

Last week at CKB I landed behind Flightcheck 88, a Challenger. It's all this rather unique shade of teal or so. From what I heard on the approach frequency they were testing a VOR. Seems like alot of jet for that job.


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[Edited 2007-06-12 04:07:19]

User currently offlineCorey07850 From United States of America, joined Feb 2004, 2527 posts, RR: 5
Reply 7, posted (7 years 2 months 2 weeks 6 hours ago) and read 8064 times:

Quoting Tornado82 (Reply 6):
Seems like alot of jet for that job.

Their Global Express is even worse, although I'm not sure if they use it for flightchecks or just transport for their big-wigs  Smile


User currently offlineJetMech From Australia, joined Mar 2006, 2687 posts, RR: 53
Reply 8, posted (7 years 2 months 2 weeks 4 hours ago) and read 8054 times:

Quoting Tornado82 (Reply 6):
Seems like alot of jet for that job.

I think that Air-services Australia ( CAA / Dept. of Aviation) used to use a Fokker F-28 for the job. I remember seeing it many times doing several approach and go-arounds along the main runway (16R-34L) at SYD. I'm not too sure what they use these days.


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Regards, JetMech



JetMech split the back of his pants. He can feel the wind in his hair.
User currently offlineUAXDXer From United States of America, joined Jul 2004, 765 posts, RR: 3
Reply 9, posted (7 years 2 months 2 weeks 2 hours ago) and read 8037 times:

Quoting Tornado82 (Reply 6):
Last week at CKB I landed behind Flightcheck 88, a Challenger. It's all this rather unique shade of teal or so. From what I heard on the approach frequency they were testing a VOR. Seems like alot of jet for that job.

The FAA's Flight Checks has 4 Challengers, most of which are used for overseas operations at US military bases.

N85

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N86

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N87

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N88

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It takes a bug to hit a windsheild but it takes guts to stick
User currently offlineFredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 10, posted (5 years 10 months 2 days 12 hours ago) and read 7597 times:



Quoting Corey07850 (Reply 3):
To be honest, unless you've got a degree in physics and radiowaves you wouldn't understand how it's done

Found an old thread, it seems, but decided to fill in a bit anyway.

If you want a basic conceptual understanding, it's not all that tricky. A localizer antenna array consists of a number of transmitting elements installed on a straight line perpendicular to the approach direction.

If you are on the left side of the approach, you will be slightly closer to the transmitting element on the left side of the runway than you are to the transmitting element on the right side. This means the signal from the right side element will take slightly longer to reach the aircraft than the signal from the left side element. The phase difference thus generated creates the signal telling the aircraft receiver where it is, relative to the centerline of the approach.

To change the alignment of the localizer electronically you basically need to introduce artificial delays in the signal paths from the signal generator to the antenna elements, corresponding to the desired change in direction of the localizer beam. Through an artifical delay, you simulate an antenna element being somewhat further from the aircraft than it really is.



I thought I was doing good trying to avoid those airport hotels... and look at me now.
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