NOT a primary in-flight security measure?

• A. Hardened flight deck doors
• B. CCTV monitoring of the cabin
• C. Secondary flight deck protection
• D. Airport perimeter fencing

Answer: (D)

The main idea is to distinguish measures used inside the aircraft during flight from security controls that protect the airfield and airport environment. Hardened flight deck doors prevent unauthorized access to the cockpit, directly safeguarding the crew and flight controls in flight. CCTV monitoring of the cabin provides real-time visibility to detect suspicious behavior and coordinate a response during the flight. Secondary flight deck protection adds additional barriers to the cockpit, enhancing defense if the primary door is breached. Airport perimeter fencing, while essential for overall airport security, acts on the ground to secure the airfield itself rather than protecting passengers and the aircraft during flight. So it is not a primary in-flight security measure.