Aircraft Operations

Chapter 1
EN-ROUTE CRITERIA
1.1 GENERAL
1.1.1 Procedures developed utilizing en-route criteria assume normal aircraft operations. Any requirements to
satisfy Annex 6 aeroplane performance operating limitations must be considered separately by the operator.
1.1.2 Two methods can be used to determine en-route obstacle clearance areas:
a) a simplified method, which is the standard method; and
b) a refined method, which can be used when the simplified method is too constraining.
1.2 OBSTACLE CLEARANCE AREAS
1.2.1 In the simplified method, the obstacle clearance area is divided into a central primary area and two lateral
buffer areas. In the refined method, the obstacle clearance area is divided into a central primary area and two lateral
secondary areas. The width of the primary area corresponds to 95 per cent probability of containment (2 SD). The total
width of the area corresponds to 99.7 per cent probability of containment (3 SD).
1.2.2 Reductions to secondary area widths
Secondary areas for en-route operations may be reduced when justified by factors such as:
a) relevant information on flight operational experience;
b) regular flight inspection of facilities to ensure better than standard signals; and/or
c) radar surveillance.
1.2.3 Area without track guidance
When track guidance is not provided, for example, outside the coverage of navigation facilities along the route, the
primary area splays at an angle of 15° from its width at the last point where track guidance was available. The width of
the buffer area (simplified method) or the secondary area (refined method) is progressively reduced to zero, ending in
an area without track guidance where the full minimum obstacle clearance (MOC) is applied.
I-5-1-1 23/11/06