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 that is offset from the runway centerline, often by up to 30 degrees, requiring a visual maneuver for final alignment.
Many LDAs require DME and some include a glideslope (designated as LDA/Glideslope), which can sometimes offer minimums comparable to an ILS, but may also come with unique challenges such as extended glideslope intercepts, specific visibility requirements, or aircraft category restrictions.
Due to the significant variability in their features, requirements (e.g., mandatory glideslope, specific equipment), and operational complexities (e.g., terrain, obstacles), pilots must thoroughly review each individual LDA procedure as the "LDA" designation itself provides limited information.

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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.