It has been a requirement for States to publish obstacle data within their
Aeronautical Information Publication (AIP) for many years. However, the
requirement was to provide this information in a simple, textual form, classified in
one of three ways:
Impacting the en-route phase of flight;
At the aerodrome and impacting the circling area;
At the aerodrome and impacting the approach / take-off phases of flight.
Information relating to terrain has only been required in a very limited form, for
runways for which Category (CAT) II/III operations are approved. This terrain
information is provided graphically by way of the Precision Approach Terrain
Chart (PATC), specified by ICAO Annex 4.