Sign in to follow this  
Guest Stratus_Fractus

How do you perform an LDA approach?

Recommended Posts

I noticed that some airports (KAMA rwy 22, for instance) have an LDA approach instead of ILS. Why is this, and how are they performed?GS

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Usually LDAs are used when for whatever reason a straight-in ILS won't work. For example, Honolulu International has one on runway 26L because there's a tall hill/mountain straight out from the end of the runway.But, looking at the Amarillo plates, I don't see why it has an LDA and not a regular ILS approach. Perhaps it's that 35 foot high tower just off the east end of the approach.If I'm not mistaken, St. Louis has some LDAs (at least FS2k2 shows them), and I know for sure La Guardia has one.I generally fly them like I would any other ILS approach, except that I have to make a correction towards the end since it's not lined up perfectly. Some, like AMA and LGA are a few degrees. Honolulu, however, is more like 45 degrees. In instances like that, there are often lead-in lights which you fly over once you see them to guide you onto the runway (I'm not sure if HNL has these or not).Anyways, that's my take on them.....anyone out there who's a real pilot, feel free to correct.

Share this post


Link to post
Share on other sites

LDA stands for localizer-type directional aid and is used instead of a standard localizer or ILS approach for the reasons stated above and possibly--although I'm not totally sure(I'm guessing here)--due to it being less expensive at some airports than a full blown ILS.It's name--"localizer-type directional aid" pretty much explains how to fly it. You'd fly it like a localizer approach--in other words--an ILS approach with not glide slope. It's sensitivity --(it's been a long time since I've taught instruments to anyone--almost 20 years-so the numerical details are a little foggy) is slightly less precise (again--I'm pretty sure of this) than a standard localizer but much more sensitive than a standard VOR approach--therefore--generally speaking-descent minimums and visiblity minimums are generally higher than for a localizer and of course higher than an approach with a glide slope. There are on occasion--again I'm reaching way back in my brain--as it's a rare thing; but there are on occasion LDA's with glide slope guidance around ( I think).Also--many LDA approach's may not be lined up with the centerline of the runway--but--many localizer approaches and even some ILS's are that way also.Another type of approach you may see that is similar to the LDA and somewhat rare is the SDF approach--standing for "simplified directional facility". It's sensitivity is greater than the VOR approach but less precise than an LDA or localizer approach--but is flown the same way. Again--for whatever reason--including economic--some airports have SDF approaches instead of LDA's.The short answer --fly it like you do a localizer or a VOR approach--tracking your needles and attempting to bracket down a heading that corrects for the wind and keeps the needle centered preferably within one dot on your HSI or VOR.AQ

Share this post


Link to post
Share on other sites

LDA is just as accurate as a Localizer, just not aligned with the runway. Fly it just like you would a localizer, vor, or gps approach. Here's an excerpt from the AIM:c. 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. Matt

Share this post


Link to post
Share on other sites

>Usually LDAs are used when for whatever reason a straight-in >ILS won't work. For example, Honolulu International has one >on runway 26L because there's a tall hill/mountain straight >out from the end of the runway. >A month or so ago a 747 driver (IIRC China Air) decided to come straight in 26L, goes right over Waikiki. The locals were not pleased!!Off the topic, but I was in the back of a Cessna 402 (behindco-pilot seat) a little while ago coming back from PHMK with Kona winds so we came in on 22L. First time ever on that approach, very nice right over town. Give it a try some time.scott s..

Share this post


Link to post
Share on other sites

An LDA that I run alot is the LDA Rwy 6 approach into KROA. The LOC is offset by 10 deg. at 70 deg mag. It has a glideslope that becomes unusable at the MM (which is also the MAP). The LDA is present solely because of terrain (which if you get good mesh for the area, it is clear why). In fact, the airport is surrounded by mountains on all sides - bad place to put an airport but great for simming :)My father used to be an ATC at KROA, and he told me that pilots experienced with the approach fly the LOC a bit to the right (within the margins of course) to make the left turn onto the rwy less severe. I've observed the UPS and FEDEX heavies land Rwy 6 in the wee hours of the morning and this seems to be what they do (but I can't really tell without being on the plane, of course). The opportunities to see this are rare. The prevailing winds usually call for an ILS rwy 33 or visual rwy 24 approach. But in light winds, LDA 6 is preferred during IMC because the Missed Approach Procedure is better/easier for 6 than for 33 (which involves a higher the risk of smacking into a moutain).Anyway, I recommend flying the approach to everyone. It's alot of fun and hard to get right. As much as I've flown it, I still land beyond the tdze alot of the time.-T Edwin (hoo)

Share this post


Link to post
Share on other sites

hi,good information here,but there are still some things missing I think.An LDA is as much precise as a normal LOC,it's just an offset,thus not properly aligned with the runway. It's a non-precision appraoch,as there usually is no glideslope. Minimums will be higher than a normal ILS CATI because it's a non-precision+there is an offset.so you would descend to the MDA until you have the runway insight and then continu visually (performing the turn visually and manually)

Share this post


Link to post
Share on other sites

If I remember correctly, the famous checkerboard approach into Kai Tak was "IGS 13."Is that right? If so, what is "IGS?"Oh, and while you're at it, what was the checkerboard for? Some sort of visual reference, I assume, but visual to what?

Share this post


Link to post
Share on other sites

The LDA to runway 19 at DCA can get interesting, minimums of about 700AGL and 2SM. If you get just a little off to the left you bust Capitol Hill restricted airspace. The turn to the runway is done at low alititude, and you're usually stabilized at only a few hundred feet or so. Then combine that with a 6800 ft runway, in bad weather, high winds and a largish plane for that runway ie 757 and you get the picture.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this