ICAO reference
4 AREA NAVIGATION (RNAV) DEPARTURE PROCEDURES AND RNP BASED DEPARTURE PROCEDURES
4.1 The general principles of RNAV and RNP-based approach procedures apply also to RNAV and RNP-based departures.
4.2 Departures may be based on RNAV VOR/DME, RNAV DME/DME, basic GNSS or RNP criteria. Most FMS-equipped aircraft are capable of following RNAV procedures based on more than one of the above systems. However, in some cases the procedure may specify constraints on the system used.
4.3 To follow a procedure based on RNP, the RNAV system must be approved for the promulgated RNP and it is assumed that all navaids on which the RNP procedure is based are in service (see NOTAMs related to DME stations, GNSS, etc.).
4.4 A route may consist of segments where different RNP values are applicable. Note that the segment with the lowest RNP value is the most demanding one for the flight. Prior to the flight, the pilot must verify that the aircraft is able to meet the RNP requirements specified for each segment. In some cases, this may require the pilot to manually update the aircraft’s navigation system immediately before take-off.
4.5 During the flight, the pilot must check that the system complies with the RNP requirements of the current segment. The pilot must also check in particular the RNP changes along the route.
4.6 The pilot will use the system's information to intervene and keep the flight technical error (FTE) within the tolerances established during the system certification process.
4.7 There are for kinds of turns:
a.
turn at a fly-by waypoint;
b.
turn at a fly-over waypoint;
c.
turn at an altitude/height; and
d.
fixed radius turn (generally associated with procedures based on RNP).