Flight Warning Systems (FWS): Alert Priorities, CWS, and Crew Response

022-12-02Pablo Asensio Martínez2026-03-272 min

System Overview

The Flight Warning System (FWS) continuously monitors aircraft sensors to detect abnormal conditions. It uses an internal logic to prioritize these conditions and present them to the crew via visual, aural, and tactile means.

Modern aircraft integrate these functions into systems like EICAS (Engine Indication and Crew Alerting System) on Boeing or ECAM (Electronic Centralized Aircraft Monitor) on Airbus.

Alert Hierarchies

Alerts are typically classified into three priority levels:

Level Priority Visual Aural Crew Action Examples
Level A Warning Red Master Warning + Message Continuous (Bell, Siren, Voice) Immediate recognition and corrective action. Engine Fire, Overspeed, Stall, Cabin Altitude, Config.
Level B Caution Amber Master Caution + Message Single/Repeated Tone (e.g., chime) Immediate awareness, subsequent action. Hyd Sys Fail, Gen Fault, Fuel Low, Brake Hot.
Level C Advisory Any (e.g., White, Cyan) except Red/Green None Awareness. System Status, Memo messages.

Handling Procedure

A standard discipline for handling alerts (especially Cautions/Warnings) is:

  1. Acknowledge the failure (Identify the light/message).
  2. Silence the aural warning (if applicable/allowable).
  3. Initiate the appropriate procedure (Read ECAM/EICAS checklist).
  4. Advise ATC (if the failure affects flight profile or capability).

Components

Central Warning System (CWS)

  • Annunciator Panel: A panel containing specific lights for various systems, centralized to minimize scan time.
  • Master Warning/Caution Lights: Located in the pilot's primary field of view (glare shield) to draw attention to the CWS or EICAS/ECAM.

Audio & Tactile Alerts

  • Aural: Designed to attract attention through a different sensory channel.
    • Fire: Bell.
    • Overspeed/Config: Siren or Clacker.
    • AP Disconnect: Cavalry Charge, Wail, or Tone.
  • Tactile:
    • Stick Shaker: Vibration of the control column for Stall Warning.

Specific Scenarios

  • Autopilot Disconnect: Deliberate or uncommanded disconnect triggers a Red Warning light and a Continuous Aural alert until acknowledged (silenced) by the crew.
  • Overspeed: Exceeding VMO/MMO triggers a Master Warning and a specific aural alert (overspeed clacker/siren).