Instrument approach
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Instrument approaches are precision or non-precision.
[edit] Precision approaches
- ILS: HF radio frequencies provide vertical ("glideslope") and lateral ("localizer") guidance. ILS approaches may be CAT I, CAT II, CAT III. CAT I approaches have a DH >= 200 feet, CAT III C has no DH.
- GPS: Augmented GPS used to provide vertical and lateral guidance. (In the US, the augmented system is called WAAS.) Unlike an ILS, WAAS doesn't require equipment at each airport, so there are now more airports in the US with WAAS approaches than with Category I ILS approaches.
- LPV, localizer performance with vertical guidance, are high-precision WAAS approaches, and don't need special aircrew training. Minima are 200 feet DH and 1/2 mile visibility. List of aiports with published LPV approaches.
[edit] Non-precision approaches
- Visual approach
- VOR approach: use a VOR plus a stopwatch to get you to roughly where you want to be. Thankfully, there are now more GPS-based approaches than VOR-based approaches in the US.
- VOR-DME approach: similar to VOR approach, except you also have distance information available, so the stopwatch isn't as important.
- Localizer approach: an ILS approach, except you don't have a glideslope.
- Circle-to-land approach: a visual approach that isn't straight-in. Nice description.
- NDB approach: the most ridiculous approach, involving zig-zagging around an NDB. High minimums, usually.
