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d. Nondirectional Radio Beacon (NDB) SSVs. NDBs are classified according to their intended use. The ranges of NDB service volumes are shown in 

TBL 1 − 1 − 2. The distance (radius) is the same at all altitudes for each class. 

<img src='content_image/530420.jpg'>

## 1 − 1 − 9. Instrument Landing System (ILS) 

## a. General 

1. The ILS is designed to provide an approach path for exact alignment and descent of an aircraft on final approach to a runway. 

2. The basic components of an ILS are the localizer, glide slope, and Outer Marker (OM) and, when installed for use with Category II or Category III instrument approach procedures, an Inner Marker (IM). 

