Home' RTCA Documents for Review : DO-201B User Requirements for Navigation Data Contents ED-77A/DO-201BforOpenConsultation/FRAC
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GENERAL REQUIREMENTS AND STANDARDS
CALCULATION CONVENTION STANDARDS
The position of navigation fixes define routes of flight and are often calculated based on
radials or bearings, and distances from ground-surveyed navaids. This section outlines
standard rules and conventions that should [NAV-D005] be followed when calculating
fixes and tracks for navigation procedures.
Many navigation fixes will be points in space that are determined by calculation from a
ground surveyed position without the benefit of a defining navaid radial or bearing. For
example, the runway end coordinates would be used in the calculation of a final
approach fix for a stand-alone approach. Enroute, airspace boundary, and approach
area fixes are other examples of calculated positions. The accuracy of calculated
positions depends on the accuracy of input parameters used and algorithms used,
therefore the impact of calculation methods affecting accuracy should [NAV-D006] be
For PBN operations, data provided by responsible authorities must ensure that the flight
path followed by the aircraft is flyable, predictable, repeatable, reliable, and identical to
the desired flight track expected by airspace authorities. In addition, an aircraft equipped
with a system such as a FMS is expected to be able to emulate the procedure track as
intended (subject to airframe limitations) by the civil aviation authority. Otherwise, the
aircraft may not be able to remain within the airspace limits.
ICAO PANS-OPS and FAA 8260.3c United States Standard for Terminal Instrument
Procedures (TERPS) provide detailed considerations for both non-PBN and PBN
procedure design. Adherence to these design standards is essential to ensure
appropriate quality of navigation data.
The following sections provide additional considerations to ensure that the calculated
data meet the needs for PBN operations.
Use Geodesic Formulas for Calculations
Refer to DO-229E Appendix L for calculation algorithms for geodesic bearing and
Standard Rules for Track Values
Responsible authorities are expected to make track values available in both degrees
true and magnetic to assure track repeatability. At high latitudes, only true track
information may be published.
The aviation industry requires that standard methodology be used in applying magnetic
variation and station declination to true track values at navaids and fixes. This standard
methodology is especially significant when using PBN non-preferred route segments.
Refer to DO-283B 18.104.22.168 .8. and PANS-OPS ICAO Doc 8168 Vol II Chapter 4 Section
2 Chapter 1.11.1 .1. for information on how magnetic variation is applied for PBN
applications. The following subsections provide additional guidance for certain cases.
Commentary: There is a common misunderstanding about the definitions of “station
declination” and “magnetic variation” and how each is applied, refer to definitions in
Appendix B. “Station declination” is the difference between magnetic and true North
resulting from the alignment of a VOR to magnetic North at the time of calibration. It is
used to define magnetic tracks to/from the VOR and is the same as the local magnetic
variation at that point in time. The station declination of the VOR never changes until a
recalibration of the VOR occurs. “Magnetic variation” on the other hand is the
published magnetic variation for an area, such as an aerodrome. Often determined by
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