Instrument Display Colour Coding

The Logic Behind Instrument Display Colour Coding

Instrument colour coding in aviation is designed for rapid recognition and unambiguous interpretation. The system is consistent across most modern aircraft, especially in electronic flight instrument systems (EFIS) and engine/system displays.

Key Colour Meanings

• Green: Indicates normal operation, active modes, or engaged functions. On engine and system gauges, the green arc shows the safe operating range.
• Yellow/Amber: Signals caution or abnormal conditions. The yellow arc on dials marks the cautionary range—parameters here require increased attention but are not immediately hazardous.
• Red: Represents warnings, exceedances, or hard limits. Red lines or arcs indicate values that must not be crossed for safety reasons.
• White: Used for current values, information, or armed (but not yet engaged) modes.
• Cyan/Blue: Denotes non-active information, background elements, or sky depiction on attitude displays.
• Magenta: Highlights command information, such as flight director bars or selected headings. (Note: Some manufacturers, like Airbus, may use green for active routes instead.)
• Brown/Tan: Typically used for terrain depiction.

Instrument Markings: Green Arc, Yellow Arc, Red Line

• Green Arc: Normal operating range—safe to operate within these values.
• Yellow Arc: Caution—operate here only with heightened awareness or for limited periods.
• Red Line/Mark: Maximum or minimum limit—never exceed.

Application on Modern Displays

On a Primary Flight Display (PFD), the layout follows the 'basic T' principle: airspeed (left), attitude (centre), altitude (right), and heading (bottom centre). Colour coding is used throughout, from flight mode annunciators (where green means engaged, white/cyan means armed) to system synoptics and alerting messages.

This standardisation ensures that regardless of aircraft type, pilots can interpret display information quickly and accurately, especially under high workload or abnormal situations.