Not Quite an ILS

Among these procedures youll find a surprising variety of features. But here are the common threads: The LDA is made up of a localizer transmitting a course signal with the expected beam width of three to six degrees, but it will be offset by as much as 30 degrees, even when advertised with a specific runway.

Elaine Kauh

Wednesday, September 14, 2016 at 12:00 AM ET

Verified

Key Takeaways:

Localizer-Type Directional Aids (LDAs) are uncommon approaches (around 25-30 in the NAS) characterized by a localizer signal that is intentionally offset by up to 30 degrees from the runway centerline, often requiring a visual maneuver for final alignment.
LDA approaches are highly diverse; some require DME, many incorporate a glideslope (labeled "LDA/Glideslope"), and their minimums and operational restrictions vary significantly based on terrain, obstacles, and specific design.
Due to their unique and varied characteristics, pilots must meticulously review each LDA approach chart, as the procedure's name alone does not convey critical details such as required glideslope, minimums, or aircraft category limitations.

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There are only 25 or so Localizer-Type Directional Aids in the National Airspace System, according to the Instrument Procedures Handbook. When accounting for multiple approaches from one LDA facility, you’ll find around 30 approach procedures sprinkled across the system.

So unless you’re flying to places like Sitka, Alaska; Honolulu, Hawaii; or Fayetteville, Arkansas; it’s uncommon to encounter or need this kind of approach. But they are around.