The air-law course's aviation-security lesson built the fence: Annex 17's definitions, its objective and its preventive standards, and the script for a seized aircraft. This lesson is the operator's side of the same fence: the EU regulation that turns Annex 17 into common European rules, the commander's transponder protocol when interference happens anyway, and the training, search and reporting machinery the operator must keep ready.
The vocabulary of security
Most of the terms come in the EU regulation's own wording, the rest in Annex 17's, and each earns its place. Security itself keeps the recalled Annex 17 sense: the combination of measures and human and material resources intended to safeguard civil aviation against acts of unlawful interference. Screening is the application of technical or other means intended to identify and/or detect prohibited articles. A security restricted area is that area of airside where, in addition to access being restricted, other aviation security standards are applied. An aircraft security check is an inspection of those parts of the interior to which passengers may have had access, together with an inspection of the hold; its bigger sibling, the aircraft security search, inspects the interior and accessible exterior. And unidentified baggage keeps its Annex 17 definition from the air-law course: baggage not picked up by or identified with a passenger. The objectives read straight off the regulation's first article: common rules to protect civil aviation against acts of unlawful interference that jeopardise its security, achieved by common rules and basic standards plus the mechanisms that monitor compliance.
Two rulebooks, one fence
The relationship between the two rulebooks is one sentence of the regulation: Regulation (EC) No 300/2008 establishes the EU's common rules and provides the basis for a common interpretation of Annex 17 to the Chicago Convention. Annex 17 sets the international standards; the regulation makes them uniform, enforceable European law, and builds a ladder of programmes to carry them: every Member State draws up, applies and maintains a national civil aviation security programme, every airport operator an airport security programme, and every air carrier an air carrier security programme. On the aircraft itself the operations rules add the hardware: a secure flight crew compartment door, required on aeroplanes over 54,500 kg, over 45,500 kg with more than 19 passenger seats, or with more than 60 passenger seats, lockable and unlockable from either pilot's station, closed prior to engine start, and locked when security procedures or the pilot-in-command so require, until engine shutdown after landing, with means to monitor the whole door area from either pilot's station and means for the cabin crew to notify the flight crew of suspicious activity or security breaches in the cabin. ICAO's Annex 6 words the same door more strictly, closed and locked from the closing of the external doors after embarkation until one opens for disembarkation, save for authorised access, the picture the air-law course's aviation-security lesson teaches; the EU operating rule above is the version this course's operators fly by.
Squawking trouble
When interference happens in flight, the transponder speaks for a crew that may not be able to. The pilot-in-command shall attempt to set the transponder to Mode A Code 7500 to indicate the situation, and if circumstances so warrant, Code 7700 should be used instead. The commander's radio duties are the recalled seized-aircraft script: endeavour to notify the appropriate ATS unit of the fact and any significant circumstances; unable to notify, continue on the assigned track and cruising level at least until able to notify or until within radar or ADS-B coverage; and if forced to depart from the assigned track or level without radiotelephony contact, broadcast warnings on the channel in use and the emergency frequency and fly the regional contingency or level-offset procedures the air-law course priced. The protocol's last move is its cleverest: a controller who sees 7500 will ask the crew to confirm the code, and the pilot shall, according to circumstances, either confirm it or not reply at all. Silence is an answer: if the pilot does not reply, ATC takes this as confirmation that the code is not an inadvertent false selection. A hijacker listening to the frequency hears nothing; the system hears everything.