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Wolfko

A question for the more adv. pilot, LOC DME and LDA DME

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Good question:Here is some more dope. An LDA is usually because of some kind of obstacle in the approach path (If I recall DCA has one to keep out of restricted airspace)and at an offset (not aligned with the runway).A quick cut and paste from another website:Localizer Type Directional Aid (LDA) 1. The LDA is of comparable use and accuracy to a localizer but is not part of a complete ILS. The LDA course usually provides a more precise approach course than the similar Simplified Directional Facility (SDF) installation, which may have a course width of 6 or 12 degrees. 2. The LDA is not aligned with the runway. Straight-in minimums may be published where alignment does not exceed 30 degrees between the course and runway. Circling minimums only are published where this alignment exceeds 30 degrees. 3. A very limited number of LDA approaches also incorporate a glideslope. These are annotated in the plan view of the instrument approach chart with a note, "LDA/Glideslope." These procedures fall under a newly defined category of approaches called Approach with Vertical Guidance (APV) described in paragraph 5-4-5, Instrument Approach Procedure Charts, subparagraph a7(:(, Approach with Vertical Guidance (APV). LDA minima for with and without glideslope is provided and annotated on the minima lines of the approach chart as S-LDA/GS and S-LDA. Because the final approach course is not aligned with the runway centerline, additional maneuvering will be required compared to an ILS approach. http://mywebpages.comcast.net/geofa/pages/rxp-pilot.jpg

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Guest av84fun

Here's an excerpt from an exceptionally thorought site relating to simulator navigation. There are hours and hours of study provided at this site.But to add my 2c, the addition of DME to a LOC/DME or LDA/DME means just what is says...i.e. a functioning DME capability is required to fly that approach."LDA Approach vs. Localizer Approach ... Is there any difference?Not much, actually. If you've thumbed your way through an FAA volume of instrument approach plates you'll have noticed an occasional heading such as LDA Rwy 2, and the like. Although they're not common, you may encounter a Localizer-type Directional Aid in your Flight-Simulator travels. If you stay on course with a conventional localizer approach it will roll you down the centerline of the runway. That's why Cat II and Cat III ILS approaches are possible. The LDA is the same as a localizer, but off-set from the runway heading. It provides course guidance down to a point from which you can proceed to the airport by visual references. Terrain features generally force the installation of an LDA approach system; it's the skyscraper, or 1000-ft. TV tower, or granite hill on the normal approach path that prevents using the conventional localizer." http://www.navfltsm.addr.com/loc.htm

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Guest UweR

Hello,thanks for the feedback so far, but details, details... I still don

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Hi, Uwe and everyone.There is a significant difference between LOC and LDA. The DME is clear to everyone.The LOC is Always aligned with the center of the runway and it

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Hi, Michael.The LOC does not have to be with the GS, if it is it's an ILS. What I wanted to point out is that the LOC is aligned with the runway centerline as part of a precision approach, ILS. You missed the part where I said that

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I think it may just be a nomenclature problem - by definition (in the US) a LOC approach is always aligned with the runway and an LDA is not. Since the LOWI LOC/DME is offset from the runway center line, then it should be (once again, in the US) considered an LDA approach. This nomenclature may not hold outside the US.DJ

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Guest UweR

Thanks for an interesting discussion!I have attached a scan of the the LOWI approach in question, just to make sure you

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Would it be correct to say that LOC antennas are located after the end of the runway whereas an LDA would be locatedclose or offset to the threshold? In other words, a LOC beam includes the runway to its end but an LDA bean terminates near the beginning.Notice on the LOWI chart the note that DME is 0 at the threshold. Also note the 2220 AGL for the straight in minimum meaning the last five miles to threshold requires visual contact.

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As I see it, a LOC beam is more precise than a LDA beam (at least at LOWI the LOC is not different to a regular ILS LOC)As you can see from the following text, also an ILS can be offset."The ILS Has Five ComponentsPart 1 the Localizer The localizer at departure end of runway provides lateral references. Frequencies are 108.l by odd tenths to 111.9. It is identified by "I" (..) as first of four letters. Fan width varies from 3 to 6 degrees and may not be aligned with the runway. It is useable within 35 degrees of course. An LDA

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