How many types of lavatory smoke detectors are found on United aircraft?

• A. 2
• B. 3
• C. 4
• D. 5

Answer: (B)

Lavatory smoke detection uses more than one sensing method so different kinds of fires can be detected reliably without frequent false alarms. Ionization detectors respond quickly to flaming fires with fine smoke particles. Photoelectric detectors are more responsive to smoldering fires, which produce visible smoke. Dual-technology detectors combine both methods to cover a broader range and reduce nuisance alarms. United’s lavatories use all three technologies across its fleet, so there are three types of detectors in use. If there were only two, one of these detection approaches would be missing; if there were four or five, that would imply additional detector types not used in these lavatories.