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

Chapter 3
DME/DME RNAV
3.1 GENERAL
3.1.1 Area navigation systems which use the procedure must be controlled through a navigation database.
3.1.2 Reference facilities
3.1.2.1 As it is not possible to know which DME facilities the airborne system will use for a position update, a
check should be made to ensure the appropriate DME coverage is available throughout the proposed route, based upon
at least two selected facilities (the coverage of DME stations is given in Figure III-1-3-1). This check should include:
a) the promulgated maximum range of the DME facility, taking the theoretical maximum radio horizon of the
station into account (maximum 370 km/200 NM);
b) maximum and minimum intersection angle of the DME stations (between 30° and 150°); and
c) promulgated DME sectorization (if any).
3.1.2.2 Alternatively, the route may be assessed using a computer model that replicates the airborne system. The
facilities selected should be published.
Note.— Airborne systems normally place all DME facilities within a maximum range (normally 370 km (200 NM))
in an update file. From that file systems use various algorithms to determine the most suitable facilities to use to
determine the most probable position.
3.2 AIRBORNE AND GROUND EQUIPMENT REQUIREMENTS
FOR DME/DME PROCEDURES
3.2.1 For procedures based on DME/DME, the calculation of cross-track tolerance (XTT), along-track tolerance
(ATT) and area semi-widths are obtained from a conservative assumption that the chosen DME facility for position
update may be located at a maximum reception range. To meet these criteria, the minimum equipment requirements
must be satisfied, as listed below.
3.2.2 The standard assumptions for airborne and ground equipment on which DME/DME procedures are based
are as follows.
a) For airborne equipment, either,
1) at least a single FMC capable of DME/DME navigation and capable of automatic reversion to updated IRS
navigation. This FMC shall be approved for operations within the TMA; or
III-1-3-1 23/11/06