Rauchmeldesystem

Überblick

The smoke detection system provides early warning of combustion events before they develop into open flames, giving flight crews time to initiate protective actions — diverting, discharging suppression agents, or isolating ventilation — while the situation remains manageable. Unlike thermal detectors, which require substantial heat build-up before triggering, smoke detectors respond to the particulate by-products of smouldering materials, providing minutes of additional warning time. The system covers the zones where undetected smouldering poses the greatest risk: cargo compartments, lavatories, avionics equipment bays, electronic equipment bays (E/E bays), and crew rest compartments on long-range wide-body aircraft.

Funktionsweise

Two detection technologies are used in aviation smoke detectors. Photoelectric detectors illuminate a sensing chamber with an LED or laser diode; in clean air, the light beam passes to an absorber without reaching the photodetector. When smoke particles enter the chamber, they scatter light onto the photodetector, triggering an alarm. This technology responds best to larger smoke particles produced by smouldering combustion. Ionisation detectors use a small radioactive source (typically Americium-241) to ionise air in a sensing chamber; smoke particles attach to the ions, reducing current flow and triggering an alarm. Ionisation detectors respond better to smaller particles from flaming combustion.

Aspirated smoke detection systems actively draw air samples from multiple points in the protected zone through a network of sampling tubes into a central detection unit, allowing a single sensitive detector to monitor a large volume with rapid response. These systems are used extensively in cargo compartments where continuous air sampling through perforated liner panels provides comprehensive coverage. Detected smoke activates aural and visual warnings in the cockpit, identifying the specific zone affected so the crew can respond appropriately.

Hauptkomponenten

Photoelectric Detector Units: Self-contained units with integral alarm relays and BITE capability. Typically mounted in lavatories, crew rest areas, and avionics bays where continuous air circulation brings samples past the detector.

Aspirated Sampling Networks: Perforated sampling tubes running through cargo hold liners, drawing air by differential pressure or a small aspiration fan to a central detector. Loop configurations provide redundancy against tube blockage.

Smoke Detection Control Unit: Receives signals from all detectors, applies voting logic to prevent single-detector false alarms, and drives the cockpit warning system. Built-in test functions verify detector sensitivity at maintenance intervals.

Cargo Compartment Liners: Perforated panels forming the sampling inlet network for aspirated systems; also serve a structural fire-containment function in Class C compartments.

Anwendungen bei Flugzeugen

The Boeing 737-800 uses photoelectric detectors in lavatories and forward/aft cargo holds. The Airbus A320 employs a similar arrangement. Long-range aircraft such as the Boeing 777-300ER and Boeing 787-9 add smoke detection to crew rest compartments accessible via overhead hatches — regulatory requirements specify that crew rest areas must be monitored because personnel may be asleep during a smouldering event. The Airbus A380-800 incorporates smoke detection across both main and upper cargo decks, crew rest areas, and multiple avionics bays distributed along the lower fuselage.

Advantages & Limitations

Smoke detection provides significantly earlier warning than thermal detection for smouldering events, which represent the most common in-flight fire scenario in cargo compartments. The aspirated sampling approach provides exceptional coverage of large volumes from a single sensitive detector, reducing both cost and maintenance burden. A persistent challenge is the sensitivity/false-alarm trade-off: overly sensitive detectors generate nuisance alarms from steam, cleaning agents, or dust, while desensitised detectors may miss marginal events. Airlines manage this through calibration procedures, filter maintenance, and dual-detector voting logic. Detector contamination — particularly in cargo holds exposed to diverse cargo including produce, which can off-gas organic compounds — remains an ongoing maintenance concern.