According to Acceptable Means of Compliance (AMC) and Guidance Material (GM) to Annex IV Commercial air transport operations [Part-CAT], Subpart B which is related to Operating Procedures (OP) for Motor Powered Aircraft (MPA), concerning the “Establishment of minimum flight altitudes”, AMC1.CAT.OP.MPA.145 is prescribed that:

(a) The Operator should take into account the following factors when establishing minimum flight altitudes:

(1) the accuracy with which the position of the aircraft can be determined;

(2) the probable inaccuracies in the indications of the altimeters used;

(3) the characteristics of the terrain, such as sudden changes in the elevation, along the routes or in the areas where operations are to be conducted;

(4) the probability of encountering unfavourable meteorological conditions, such as severe turbulence and descending air currents and

(5) possible inaccuracies in aeronautical charts.

(b) The Operator should also consider:

(1) corrections for temperature and pressure variations from standard values;

(2) ATC requirements and

(3) any foreseeable contingencies along the planned route.