Extract from the EAG Guide:
Minimum Obstacle Clearance Altitude (MOCA)
The MOCA calculation described below is acc to the KSS method which is one of the JAA approved methods.
MOCA is the sum of:
- the maximum terrain or obstacle elevation whichever is highest, plus
- 1000 FT for elevation up to and including 6000 FT, or
- 2000 FT elevation exceeding 6000 FT rounded up to the next 100 FT.
MOCA in hundreds of feet, is given in the RFC, SID and STAR.
The lowest MOCA to be indicated is 2000 FT (20).
MOCA is valid for a corridor of variable width as indicated below.
From a VOR station, the corridor width is defined as a borderline starting 5 NM either side of the
VOR, diverging 4° from centreline until a width of 20 NM is reached at 70 NM out, thence parallels
the centreline until 140 NM out, thence again diverges 4° until a MAX width of 40 NM is reached at
280 NM out. Thereafter the width remains constant.
From an NDB similarly the corridor width is defined as a border line starting 5 NM either side of the
NDB diverging 7° until a width of 20 NM is reached 40 NM out, thence parallels the centreline until
80 NM out, thence again diverges 7° until a MAX width of 60 NM is reached 245 NM out. Thereafter
the width remains constant.
Overlapping area is determined only at track change, viz.:
- if less than 30° adequate coverage is obtained by considering elevations within the extended
corridor borderlines
- if 30° or more the MOCA corridor is extended by a 10 NM circle from the waypoint.
Note: At waypoints with different track changes, the most conservative value applies.
Minimum Off-Route Altitude (MORA)
MORA is the sum of:
- the maximum terrain or obstacle elevation whichever is highest, plus
- 1000 FT for elevation up to and including 6000 FT, or
- 2000 FT for elevation exceeding 6000 FT rounded up to the next 100 FT.
MORA in hundreds of feet is given in the RFC.
The lowest MORA to be indicated is 2000 FT (20).
MORA is valid in an area bounded by every second LAT/LONG squares on the RFC and TAC.