What are mandatory signs?
Red panel, white inscription — the one sign on the airfield that means stop. It marks a boundary an aircraft or vehicle must not cross without an explicit ATC clearance.
Mandatory instruction signs are the airfield's stop signs: a red background with a white inscription. A black outline may edge the legend where it needs more contrast. They mark an entrance to a runway, a runway-holding position, a critical/sensitive area, or an area a vehicle or aircraft is prohibited from entering — and unlike guidance signs, that instruction is not optional. An aircraft or vehicle must hold at the sign until ATC issues an explicit clearance to proceed.
They are the deliberate inverse of an information/direction sign — yellow background, black inscription — which only guides (taxiway identification, direction, or destination) and carries no prohibition of its own. Colour coding is the entire logic of the airfield sign system: red-and-white is always mandatory, yellow-and-black is always informational, and the two are never combined on a single panel background.
Frequently Asked Questions
Q1What is a mandatory sign?
The airfield's stop sign: a red background with a white inscription, marking an entrance to a runway, a runway-holding position, a critical/sensitive area, or a prohibited area.
Q2Does a mandatory sign require ATC clearance to proceed?
Yes. Unlike guidance signs, the instruction on a mandatory sign is not optional — an aircraft or vehicle must hold at the sign until ATC issues an explicit clearance to proceed.
Q3How is a mandatory sign different from an information sign?
Colour and function are inverted: mandatory signs are red/white and prohibit movement, while information/direction signs are yellow/black and only guide, carrying no prohibition of their own.
Q4What are some examples of mandatory signs?
Runway holding position signs (runway designators, white on red), runway/runway intersection signs, NO ENTRY signs, and ILS critical/sensitive area signs.
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