AIM
12/2/21
6.
Unreliable signals may be received outside of
these areas. ATC may clear aircraft on procedures
beyond the service volume when the controller
initiates the action or when the pilot requests, and
radar monitoring is provided.
7.
The areas described in paragraph 1
−
1
−
9 b5
and depicted in FIG 1
−
1
−
6 represent a Standard
Service Volume (SSV) localizer. All charted
procedures with localizer coverage beyond the
18 NM SSV have been through the approval process
for Expanded Service Volume (ESV), and have been
validated by flight inspection. (See FIG 1
−
1
−
7.)
FIG 1
−
1
−
7
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
−
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
−
4
−
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
−
LDA/GS and
S
−
LDA. Because the final approach course is not
aligned with the runway centerline, additional
1
−
1
−
12
Navigation Aids