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 instrument approaches, characterized by a localizer course intentionally offset from the runway centerline by up to 30 degrees, necessitating a visual maneuver for final alignment.
LDAs are highly variable, with some requiring DME, others including a glideslope (labeled "LDA/Glideslope"), and minimums that can range widely from near-ILS precision to significantly higher.
Due to their unique characteristics, such as specific offset angles, terrain challenges, required equipment (e.g., mandatory glideslope), and operational limitations (e.g., aircraft category restrictions), pilots must meticulously examine each individual LDA approach chart.

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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.