Aircraft Operations. Volume II - Construction of Visual and Instrument ...

Chapter 1
DEFINITIONS
When the following terms are used in this document, they have the following meanings:
Aerodrome elevation. The elevation of the highest point of the landing area.
Along-track tolerance (ATT). A fix tolerance along the nominal track resulting from the airborne and ground
equipment tolerances.
Altitude. The vertical distance of a level, a point or an object considered as a point, measured from mean sea level
(MSL).
Area minimum altitude (AMA). The lowest altitude to be used under instrument meteorological conditions (IMC)
which will provide a minimum vertical clearance of 300 m (1 000 ft) or in designated mountainous terrain 600 m
(2 000 ft) above all obstacles located in the area specified, rounded up to the nearest (next higher) 30 m (100 ft).
Note.— In the exact calculation 984 feet can be used as an equivalent to 300 metres.
Area navigation (RNAV). A method of navigation which permits aircraft operation on any desired flight path within
the coverage of the station-referenced navigation aids or within the limits of the capability of self-contained aids, or
a combination of these.
Base turn. A turn executed by the aircraft during the initial approach between the end of the outbound track and the
beginning of the intermediate or final approach track. The tracks are not reciprocal.
Note.— Base turns may be designated as being made either in level flight or while descending, according to the
circumstances of each individual procedure.
Change-over point. The point at which an aircraft navigating on an ATS route segment defined by reference to very
high frequency omnidirectional radio ranges is expected to transfer its primary navigational reference from the
facility behind the aircraft to the next facility ahead of the aircraft.
Note.— Change-over points are established to provide the optimum balance in respect of signal strength and
quality between facilities at all levels to be used and to ensure a common source of azimuth guidance for all aircraft
operating along the same portion of a route segment.
Circling approach. An extension of an instrument approach procedure which provides for visual circling of the
aerodrome prior to landing.
Contour line. A line on a map or chart connecting points of equal elevation.
Cross-track tolerance (XTT). A fix tolerance measured perpendicularly to the nominal track resulting from the
airborne and ground equipment tolerances and the flight technical tolerance (FTT).
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