4/20/23 

AIM 

FIG 1

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ILS Expanded Service Volume 

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

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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

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4

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5, 

Instrument Approach Procedure Charts, subparagraph a7(b), 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

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LDA/GS and S

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LDA. Because the final approach course is not aligned with the runway centerline, additional 

maneuvering will be required compared to an ILS approach. 

d.  Glide Slope/Glide Path 

1. 

The UHF glide slope transmitter, operating on one of the 40 ILS channels within the frequency range 

329.15 MHz, to 335.00 MHz radiates its signals in the direction of the localizer front course. The term “glide 

path” means that portion of the glide slope that intersects the localizer. 

Navigation Aids 

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