How many fire detectors are mounted in each engine compartment to indicate an external engine fire?

• A. 3
• B. 2
• C. 4
• D. 5

Answer: (A)

Three detectors are used in each engine compartment to indicate an external engine fire. This arrangement provides quick and reliable detection through redundancy and full coverage around the nacelle. If heat from a fire is present, multiple detectors will sense it, so the system can warn promptly even if one sensor has a fault. A single detector could miss a fire or produce a false alarm due to a fault, so having three reduces the chance of missed detection while keeping wiring and cost reasonable. The cockpit warning and, if needed, the fire suppression sequence are then triggered when enough detectors signal heat consistently.