Aircraft Smoke Detection Systems

021-12-01Pablo Asensio Martínez2026-03-241 min

General Principles

  • Application: Smoke detectors are mandatory in areas that cannot be kept under constant physical surveillance by the crew.
    • Locations: Cargo holds, Lavatories, Crew rest areas, Electronic/Avionics bays.
    • Note: Engines and APUs typically use heat/fire loops, not smoke detectors.
  • Indication: Flight deck warnings usually include a Master Warning (Red) and specific zone lights to draw immediate attention.

Optical Smoke Detectors

These rely on the interaction of light with smoke particles.

1. Light Refraction / Scattering (Tyndall Effect)

  • Mechanism: A light source (LED) and a photocell are positioned at an angle within a dark chamber (labyrinth).
  • Normal State: Light passes into a trap/catcher; the sensor sees darkness.
  • Alarm State: Smoke particles enter the chamber and scatter/reflect the light onto the photocell.
  • Usage: Common in "point" detectors (e.g., Lavatories).

2. Light Attenuation / Obscuration

  • Mechanism: A transmitter and receiver are placed in a direct line of sight.
  • Normal State: The receiver sees full light intensity.
  • Alarm State: Smoke passes between them, blocking or attenuating the light beam.
  • Usage: Suitable for larger open areas (e.g., Cargo compartments).

Ionization Smoke Detectors

  • Mechanism: Uses a small amount of radioactive material to ionize the air between two electrically charged plates, creating a steady current flow.
  • Alarm State: Smoke particles attach to the ions, making them heavy and slow. This disrupts/reduces the current flow between the plates, triggering the alarm.
  • Sensitivity: Very sensitive to small smoke particles.