Alerting Systems

Understanding Aircraft Alerting Systems for ATPL Studies

Alerting systems are core to modern aircraft systems and flight-deck ergonomics, ensuring timely crew awareness and appropriate response to developing hazards. Under ATPL-level standards and common aviation regulations (ICAO/EASA/FAA), alerts are standardized by priority, color, and aural logic to minimize confusion and promote correct procedures. The Flight Warning System (FWS) or Crew Alerting System integrates multiple sources—sensors, avionics, and systems logic—to generate messages that are clearly categorized and prioritized. A key principle is aural prioritization: if aural signals are provided, a warning always takes precedence over a caution, preserving crew attention for the most critical conditions.

Alert categories are defined by urgency and the type of crew response required. A warning (typically red, with distinct aural cues) demands immediate recognition and corrective/compensatory action. A caution (amber) indicates that immediate awareness is required and that subsequent crew action will be required, but not necessarily at once. An advisory indicates that crew awareness is required and action may be required, often for trend monitoring or configuration checks. Examples include the stall warning system, which is fundamentally based on angle of attack measurement and warns of impending stall regardless of airspeed, and GPWS/EGPWS aural cues such as “DON’T SINK” during initial climb or go-around if altitude loss is detected. These standardized messages, colors, and tones help crews apply correct procedures consistently across aircraft types within the Instruments/Electronics domain.

TCAS II (Traffic Collision Avoidance System) enhances midair collision avoidance by providing Traffic Advisories (TAs) and Resolution Advisories (RAs). TCAS II issues avoidance guidance only in the vertical plane. Symbology is standardized: proximate traffic appears as a white or cyan solid lozenge (filled diamond), an RA intruder is shown as a red full square, and aural cues such as “Climb” or “Descend” direct the vertical maneuver. When a corrective RA is generated, pilots must modify vertical speed without delay and follow the RA even if it momentarily conflicts with an ATC instruction; coordinated RAs are possible when both aircraft are TCAS II-equipped. Correct interpretation of TA/RA symbology, aural cues, and required procedures is a major focus of ATPL training and line operations.

EGPWS extends classic GPWS by using a terrain look-ahead alerting function that references an onboard electronic terrain database of worldwide ground elevation. This predictive capability enables alerts to potential controlled flight into terrain (CFIT) risk along the projected flight path—often well before proximity triggers would occur. Together with FWS logic and standardized alert color-coding (e.g., amber for actionable but not immediately critical conditions), these systems exemplify how aircraft systems integrate sensors, databases, and human factors to guide safe, procedural decision-making.

What this question bank covers

• FWS alert levels: warning, caution, advisory (colors, aural priority)
• Stall warning fundamentals and angle of attack sensing
• TCAS II symbology, TA vs RA logic, and vertical-only guidance
• RA compliance, coordinated RAs, and immediate vertical speed changes
• GPWS cautions (e.g., “DON’T SINK”) and pilot response
• EGPWS terrain look-ahead using global elevation databases
• Standardized alert colors, crew procedures, and ATPL exam focus areas