In the 1990s there used to be two basic types of instrument approaches: precision and non-precision. How many different kinds are there now, and what are the differences.
All approaches can still be categorized as a precision or non-precision. Some of the terminology has changed, radar approaches are becoming less common and and GPS approaches are becoming more common, but the fundamentals are the same. Precision approaches still provide glideslope guidance, and non-precision approaches do not.
It may be important to note that many flight computers blur the lines some with GPS approaches. There are approaches where the plate still calls the bottom altitude an 'MDA' (instead of 'DH' or 'DA') as you would in a normal non-precision approach, but the flight computer will generate a custom glide slope to that point. Because this is generated artificially inside your aircraft and not schematically planned by a certified official, this still only qualifies as non-precision.
All in all, if you're trying to pick up instrument flying after a long break, you'll still be good to go with your basic understanding of precision versus non-precision approaches.
The FAA now issues Operations Specification C052 (Straight-in Non-Precision, APV, and Category I Precision Approach and Landing Minima - All Airports) to Part 135 (and probably very similar for Part 121) air carriers.
In that Ops Spec, they list three categories of approaches:
- Nonprecision Approach Procedures Without Vertical Guidance
- Approaches With Vertical Guidance (APV), and
- Precision Approach Procedures (ILS, MLS, & GLS)
The basic difference between the categories is whether or not you have vertical guidance that can be used for the approach and the degree of accuracy provided by the underlying navaid.
There are also some Flight Management Systems (FMS's) which calculate the vertical navigation (VNAV) component for nonprecision approaches that would not otherwise have it. These "pseudo-glideslopes" are for reference only and the pilot is responsible for verifying that all crossing restrictions are still made.