Which item is listed as an external fire cause?

• A. Any unusual circumstances outside the aircraft, either during the flight or on the ground
• B. Dropped cigarettes
• C. Electrical faults
• D. Galley oven

Answer: (A)

External fire causes come from sources outside the aircraft, either during flight or on the ground. The item that mentions “any unusual circumstances outside the aircraft” fits this idea exactly, because it attributes the fire to events occurring outside the airframe, not inside it. In contrast, the other options describe fires that originate inside the aircraft: a dropped cigarette starts a fire within the cabin, electrical faults involve internal wiring and systems, and a galley oven is equipment located inside the aircraft. So the outside-origin wording is what makes this choice the best match for an external fire cause.