Moderators: richierich, ua900, PanAm_DC10, hOMSaR

 
FrequentFlyKid
Topic Author
Posts: 1097
Joined: Thu Nov 22, 2001 5:04 am

Offset LDA ILS Approaches

Sun Sep 15, 2002 12:06 pm

Quite simply: what are they, why are they, and how are they flown?
 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 12:20 pm

What: In short, an LDA is an ILS that is not aligned with a runway, although it may or may not have a glideslope.

Why: There are a few reasons why. A major one being terrain/obstructions on or near the extended centerline of the runway. Another one is the location of the transmitter - I've seen an LDA which appeared to be transmitted from an onfield VOR.

How: They're flown exactly like an ILS or Localizer for the most part. Any more detailed differences would be an a case by case basis.
 
FrequentFlyKid
Topic Author
Posts: 1097
Joined: Thu Nov 22, 2001 5:04 am

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 12:26 pm

Thanks for you reply, however there was to be a difference. If they aren't aligned with the runway then you would fly into the ground instead of the runway.
 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 12:35 pm

If the LDA is aligned within 30 degrees of the runway it is still considered to be a "straight-in" landing. This means that when the pilot breaks out of the clouds/has the runway environment in sight, only a small amount of turning is needed to align the aircraft with the runway. If the LDA is more than 30 degrees off the runway, it is considered a "circling" landing. This means that more pronounced turns (or even a traffic pattern) are needed to align the aircraft before landing on the runway.

If you want some more info on how the pilot goes from on the approach to landing on an approach which is not aligned with the runway, just let me know.
 
Guest

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 1:03 pm

LDA approaches aren't very common. Offhand, I can only think of a couple of airports where I've used them. Elko, Nevada has a LDA-DME approach which is aligned 6 degrees off of the runway centerline and my personal favorite procedure (yeah, right), the Lindz 4 departure out of Aspen, Colorado, uses a backcourse offset LDA to keep you from flying into the mountains. (Very sporty, that departure is. Big grin ) They are, for all intents and purposes, flown just like a localizer approach.

Jetguy
 
Guest

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 7:03 pm

Too bad the old HKG airport is closed, that was an interesting approach, with the ILS offset some 43 degrees to runway 13, and obviously, the MDA was quite high (some 500 AGL)...
xxx
One that is very impressive in mountains is Innsbruck, Austria, by chance the field elevation is much lower that Aspen, but the summits still around 11,000 feet around there... the localizer is slightly offset too... Been there a few times in my young days with 727s... we only had a handful of captains qualified for that airport, due to complex missed approach procedures... MDA is some 2500 feet AGL...
(s) Skipper
 
FrequentFlyKid
Topic Author
Posts: 1097
Joined: Thu Nov 22, 2001 5:04 am

RE: Offset LDA ILS Approaches

Sun Sep 15, 2002 11:59 pm

I would like to know more about them....

 
flyf15
Posts: 6633
Joined: Tue May 18, 1999 11:10 am

RE: Offset LDA ILS Approaches

Mon Sep 16, 2002 12:16 am

Well, there are many types of instrument approaches. VOR, NDB, GPS, and ILS being the main ones, with LOC, LDA, SDF, PAR, etc being others. VOR approaches are the main one usually not aligned with the runway.

Instrument approaches have something called a missed approach point. The pilot flies the approach, always looking for the runway environment (runway, markings, lights, etc) until this point. If he does not see it by the MAP, he must execute the missed approach. There is another item called the decision height, it is the minimum altitude you can fly until you have set up a normal descent to the runway.

Upon seeing the runway, the pilot plans out a descent to the runway by visual means. Many times this just involves continuing to fly the approach (ie: staying on the ILS signals). Although, for an approach which is not aligned with the runway, "circling" is required. This usually involves flying some sort of traffic pattern, depending on where the aircraft is compared to the location of the runway for landing. The pilot circles around (is given a set distance to maintain from the airport) while always maintaining visual contact with the runway, aligns with final, and sets up for landing.

There are other times circling is used. One is when there is only an approach to one end of a runway, yet landing opposite direction is favored (for winds, traffic, etc). In which case the pilot would circle around and land going the opposite direction. Circling can also be used to fly an approach to one runway then circle and land on an entirely different runway.
 
Guest

RE: Offset LDA ILS Approaches

Mon Sep 16, 2002 12:21 am

In the simplest of terms, they are nothing more than a localizer that is aligned at an angle to the runway. It is a nonprecision approach, as is also a localizer approach. The main reason why someone would want to offset a localizer approach would be to clear obstacles or terrain which would interfere with a straight in approach. This is typically where you see them - at airports located in mountainous areas. Examples of this type of installation would be the two that have been previously mentioned in this thread, Innsbruck and Elko. I really doubt if you will be seeing too many more new installations. GPS approaches can do the same thing with little, if any, hardware for the local airports to purchase and maintain. I hope this explains it to you. Just think of a localizer approach that is offset to the runway.
 
Rai
Posts: 1697
Joined: Fri Feb 15, 2008 6:12 pm

RE: Offset LDA ILS Approaches

Mon Sep 16, 2002 3:37 am

LDA approaches aren't very common. Offhand, I can only think of a couple of airports where I've used them.

LGA uses "LDA Alpha approach" for runway 22 pretty much all the time. Unless this is something different?
 
Guest

RE: Offset LDA ILS Approaches

Mon Sep 16, 2002 8:07 am

Rai,
LDA approach procedures aren't very common. I don't have actual numbers in front of me, but I would assume that out of all of the published instrument approach procedures in the U.S. there would be only a handful of LDA procedures. Now, that doesn't mean that at the airports (Like LGA, EKO, etc.) that have them, they aren't used; they are and they are used a lot.
Jetguy
 
jcxp15
Posts: 989
Joined: Fri Jun 29, 2001 12:05 pm

RE: Offset LDA ILS Approaches

Mon Sep 16, 2002 9:49 am

As Rai Said, LGA uses LDA-A approach. I don't think it's because of any terrain obstacles, because LGA also has an ILS RWY22 approach. My guess is because most planes that come in usually fly over LGA first or up the Hudson river, and then make a "U-turn". The LDA most likely makes it easier for the captain to fly the "u-turn", especially on the sharper ones.
The only other reason I can think of, is HPN. I dunno HPN's approach or departure pattern, but maybe it allows HPN more space (although I doubt this).
I've also thought Co-op city mighta had something to do with it, but then I realized that it's not really under the approach pattern, and the planes are still too high then (at least I think).
Maybe a pilot who's flown the LDA into LGA can enlighten us.

Who is online

Users browsing this forum: MoKa777 and 8 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos