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A non-precision approach is an instrument approach and landing which utilises lateral guidance but does not utilise vertical guidance. (ICAO Annex 6)
Non-precision approaches which are pilot-interpreted make use of ground beacons and aircraft equipment such as VOR, NDB and the LLZ element of an ILS system, often in combination with DME for range. Lateral guidance is provided by a display of either bearing to/from a radio beacon on the approach track or at the airfield or, in the case of an LLZ only approach, by display of the relative position of the LLZ track on the aircraft ILS instruments and vertical guidance is based on the range from the airfield as indicated by a DME at the airfield or on track or by timing based upon passage overhead radio beacons on the track described by the designated procedure.
Non-precision approaches are often conducted with less use of automated systems than precision approaches. However, on many modern aircraft, automatic systems may be left engaged until reaching the MDA/H, or beyond.
For pilots of older aircraft, in which use of automated systems to assist in flying the approach is limited, a high degree of piloting skill is required to fly such approaches accurately and the frequent practice which many pilots need to achieve this can be difficult to come by if precision approaches are the normal method used.
A high proportion of CFIT accidents have been shown to occur during non-precision approaches. This is in part a result of loss of situational awareness, e.g. resulting in descent before the initial approach fix; and in part a consequence of the lack of precise vertical guidance, which may involve leveling off at intermediate points between the initial approach fix and MDA/H (a step-down approach).
The Constant Descent Angle Approach technique has been promoted in order to mitigate the risks inherent in the standard step-down approach. This procedure may be further simplified in use by the vertical navigation (VNAV) feature of FMS.
An example of a non-precision approach procedure is illustrated below.
Other instrument approaches which utilise lateral and vertical guidance but do not meet the requirements established for precision approach and landing operations are also classified as non-precision approaches. Examples are a Surveillance Radar Approach (SRA) or a VDF approach.
See also Aerodrome Operating Minima.
- ICAO Annex 6;
Flight Safety Foundation
The Flight Safety Foundation ALAR Toolkit provides useful training information and guides to best practice. Copies of the FSF ALAR Toolkit may be ordered from the Flight Safety Foundation ALAR website http://www.flightsafety.org/current-safety-initiatives/approach-and-landing-accident-reduction-alar