36.64 Terrain Clearance

36.64.2 Describe the determination of the minimum safe altitude for IFR flight. AIP GEN

GEN 3.3 AIR TRAFFIC SERVICES (ATS)

5 MINIMUM FLIGHT ALTITUDES

5.2 MSA 

5.2.1 The MSA is found by identifying the controlling obstacle within the total area of the navigation tolerance, based on the type and coverage of the navigation facilities, plus a designated buffer area to allow for navigational error.

5.2.2 MSA for each sector are shown on ENRC and ARC charts. These provide the basis for establishing the minimum cruising altitude appropriate to the direction of flight. The requirements for subsequent sectors should be anticipated by crossing the facility or reporting point at the appropriate altitude relative to the following sector.

MSA Obstacle Clearance 

5.2.3 The MSA provides not less than 1000 ft, or in areas designated as mountainous zones, 2000 ft clearance over all obstacles within the enroute obstacle clearance area. Where the controlling obstacle has not been surveyed, a 100 ft obstacle allowance is added.