Non-precision approaches are instrument approach procedures (IAPs) that do not include vertical guidance.
Non-precision or nonprecision approaches are instrument approach procedures (iaps) that provide lateral guidance to the approaching aircraft (keeping its flightpath aligned with and pointed at the runway), but not vertical guidance (the pilot has to manually figure out how and when to descend, sometimes with the help of air-traffic-control). In contrast, a precision-approach provides both lateral and vertical guidance.
Non-precision approaches, somewhat counterintuitively, are generally harder to fly than precision approaches, as they place greater demands on the pilot's piloting skills (as opposed to just flying the aircraft down the tunnel in the sky and having the ILS display or the PAR controller or whatnot tell you if you're in the wrong chunk of air).
Examples of non-precision approaches include:
- vor and ndb approaches utilize, as the names suggest, a VOR or NDB installation on or near the airport.
- localizer, or LOC, approaches utilize the localizer portion of an airport's ils installation; the localizer provides only lateral guidance, unlike the full ILS, but it can still be used even if the ILS's glideslope is out of service.
- Some types of rnav (gnss) approaches, which use satellite navigation (GPS) to determine the aircraft's location, provide only lateral guidance, and are, thus, non-precision approaches; other types are true precision approaches, providing both lateral and vertical guidance.
For more information, see Wikipedia.