This is taken more or less directly from our ops manual.
MSAs are shown as a screened overprint in relation to the Latitude/Longitude graticule as
follows:
a) LOW and LOW/HIGH charts -I deg Lat x I deg Long.
b) NAT charts below 56 deg N - I deg Lat x I deg Long.
c) NAT charts above 56 deg N - I deg Lat x 2 deg Long.
d) HIGH charts -2 deg Lat x 2 deg Long.
e) POLAR CHART -5 deg Lat x 5 deg Long
Aerodrome Related Charts
MSAs:
On applicable charts, e.g. Instrument Approach Charts, Arrivals Charts, Area Charts and Terrain Arrivals/Departures charts, MSAs are shown by means of Contour Envelopes.
Contour Envelope MSA figures apply to the whole of the envelope area.
The lowest (background) MSA value shown on the chart is derived by taking the
aerodrome elevation rounded up to the next 100 ft, adding 500ft and then adding the
appropriate clearance. (Up to and including 5000ft clearance of 1000ft, above 5000ft clearance of 2000ft.)
SSAs
SSAs are quoted for each of the four quadrants, centred on the Aerodrome Reference
Point and aligned on the true cardinal points N, S, E and W. Each figure is quoted as "SSA 25nm" but a 5nm margin is added to this radius. The SSA for each quadrant also
takes account of a 5nm overlap between quadrants.
The SSA is derived by taking the elevation of the highest obstacle in the quadrant
rounded up to the next lOOft, then adding the appropriate clearance. (Up to and including 5000ft clearance of 1000ft, above 5000ft clearance of 2000ft.)
NOTE: On the revised (2000 specification) Racal Aerodrome Charts quadrant SSA's are
discontinued and MSA's are specified based upon the airfield reference point (UK
standard), or the relevant radio aid as identified on the plate (Non UK) and may be split into segments.
Hope this is of help to you.
Regards
Exeng
[This message has been edited by exeng (edited 17 November 2000).]