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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.

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    $\begingroup$ I'm not sure what you mean by "type", could you explain a bit more about what you're asking? The FAA Instrument Procedures Handbook uses the word "type" to mean ILS, LOC, RNAV, contact, visual, PAR, ASR etc. but listing and comparing all of them would need a very long answer. $\endgroup$ – Pondlife Sep 25 '14 at 12:34
  • $\begingroup$ @Pondlife Poor choice of a word on my part, but I couldn't offhand think of a better at the time of posting. Now that I think about it again, I perhaps should have used "categories". What I was trying to find out, and what tmptplayer admirably answered, was whether the two "basic types" (as I chose to call them) were still thought of that way and how much things have changed in the 15 years since I've done any IFR flying. $\endgroup$ – Terry Sep 25 '14 at 18:00
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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.

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    $\begingroup$ Still non-precision on the non-official glide slopes for good reason. You can follow it, but have to monitor it as it may mislead you. I ran across one that would have put me below MDA had I followed it. Had to level off for about 30 seconds, then pick it up again to be legal. $\endgroup$ – Brian Knoblauch Sep 25 '14 at 15:46
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    $\begingroup$ @Brian You're absolutely right Brian - there are many traps in the intermediate descents for non-precision approaches which may be driven by obstacles/terrain that make a constant gradient descent unsafe. I would never endorse following a FMS generated glide slope that violates the actual approach - you must always be cognizant of the restrictions. $\endgroup$ – tmptplayer Sep 26 '14 at 5:29
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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.

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