ILS & RNAV Approaches #

General #

A lot more accurate, all the way down to the ground
Provides ground-based support, not GPS.
Includes path (localizer), altitude (glide slope), horizontal direction (marker beacons / internal marker, center market, etc.)

Different types:

Category I (CAT I): Decision at 200 feet above ground with 1,800 to 2,400 feet runway visibility.
Category II (CAT II): Decision between 100-200 feet with 1,200 feet visibility.
Category III (CAT III):
- CAT IIIa: Decision as low as 50 feet with 700 feet visibility.
- CAT IIIb: No set decision height with visibility as low as 150 feet.
- CAT IIIc: No set height or visibility limit, but not yet operational as of 2021.

Not as accurate as ILS, has higher minimums
Can be implemented at almost any airport. Since they are GPS points
RNAV-LPS (Localizer Performance with Vertical Guidance) is the most accurate / near ILS levels
Mostly relies on sattelite / GPS

Three types of RNAV localizers:

LPV (Localizer Performance with Vertical Guidance): For WAAS aircraft, most precise down to 200 feet. Uses satellite-based navigation rather than ground-based.
VNAV (Vertical Navigation): Helps flight guidance system provide vertical profile manager such as fuel efficiency, automated descent and climb, integration with FMS, approaches, etc.
LNAV (Lateral Navigation): Worst of the three. Non-precision approach with only lateral (left-right) guidance. No vertical guidance / glide slope. There are higher decision altitudes.