Definition
A cockpit device — typically a light, flag, or annunciator — that alerts the pilot when an instrument or system has failed, lost power, or is providing unreliable information. Warning indicators appear on or near the affected instrument and are designed to be immediately noticeable so the pilot stops trusting the suspect data.
Plain English
A small light or flag in the cockpit that tells you when something has gone wrong with an instrument or system, so you know not to rely on what it's showing.
Context Anchor
In analog instrument failure discussions, a pilot may see a warning indicator on or near an instrument when that instrument has lost power, lost valid information, or is no longer dependable.
Derivation
Warning comes from an old word meaning to make someone aware of danger. Indicator comes from Latin meaning to point out or show. Together, the phrase means something that points out a condition the pilot needs to notice.
Why Pilots Care
Allows immediate recognition that an instrument reading must be disregarded to avoid spatial disorientation or incorrect control inputs.
Intuition Check
Do not assume a warning indicator is the same thing as the instrument reading. The reading shows information; the warning indicator tells you whether something about that information or system may be unsafe or unreliable.
Example Sentence 1
When the red warning flag appeared on the attitude indicator, the pilot cross-checked the standby instruments and continued the flight using backup references.
Example Sentence 2
Before entering clouds, the pilot scanned each instrument for any sign of a warning indicator.