A mandatory sign is provided to identify a location beyond which an aircraft taxiing or vehicle is not to proceed unless authorised by the air traffic control. Mandatory airfield signs also include Road-holding Position signs, and No Entry signs. These mandatory guidance signs display white characters on a red background.
Taxiway Guidance Signs
Runway-holding Position Signs
Identify the designated runway-holding position associated with a particular runway, and consist of the runway designation in white on a red background. Where the runway is equipped with ILS, the runway-holding position is usually established at the edge of the critical/sensitive area in order to protect the ILS when in use. A Runway-holding positioning sign is located on the outside of the Runway-holding markings facing the direction of approach to the runway.
A NO ENTRY sign
This type of sign is installed when entry to an area is prohibited. The sign is located at the beginning of the area to which entrance is prohibited on each side of the taxiway as viewed by the pilot. it can also be classified as a mandatory sign.
Taxiway Information guidance signs
Taxiway information signs are usually yellow in color with black lettering. These are to provided assistance in directing the pilots, of maneuvering aircraft around the taxiway infrastructure.
Information guidance signs
include: direction signs, location signs, destination signs, runway exit signs, and runway vacated signs. An information sign other than a location sign is to consist of an inscription in black on a yellow background. A location sign consists of an inscription in yellow on a black background.
Taxiway location signs
These are used to identify individual taxiways. Taxiway information location signs bear the taxiway designation letter in yellow on a black background surrounded by a yellow border. Taxiway location signs are generally positioned at the approach to a taxiway intersection.