The previous lesson named the goods; this one moves them. The terminology carries over unchanged: the dangerous goods, accidents, incidents, exemptions, packagings and UN numbers defined there are the working vocabulary here, the UN number still the four-digit identity the UN Committee of Experts assigns to a substance, the exemption still an authorisation other than an approval giving a national authority's relief from the Technical Instructions. What this lesson adds is the machinery of carriage: who is allowed to carry, what may not fly at all, how a shipment is accepted, packed, inspected and loaded, and the paper that follows the goods from the shipper's declaration to the commander's NOTOC and the reports after something goes wrong.
Who may carry, and what may fly
The regime's scope is deliberately total. The transport of dangerous goods by air shall be conducted in accordance with Annex 18 as amplified by the Technical Instructions, and the guidance spells out the reach: that requirement applies irrespective of whether the flight is wholly or partly within or wholly outside the territory of a State, and irrespective of whether an approval to carry dangerous goods is held at all. The approval gates the carriage, not the rules: dangerous goods shall only be transported by an operator approved for it, except for goods not subject to the Instructions under their Part 1 or carried by passengers or crew members, or in baggage, under their Part 8. To earn the approval the operator establishes, per the Instructions, a training programme for all personnel involved and operating procedures ensuring safe handling at all stages: the policy, acceptance, handling, loading, stowage and segregation, accident and incident actions, emergency response, contamination removal, everyone's duties, inspection for damage, leakage or contamination, and the reporting.
What may fly is a three-tier gate. The baseline: the transport of dangerous goods by air shall be forbidden except as established in the Annex and the Technical Instructions. Above it, some goods, including those the Instructions identify as forbidden in normal circumstances, and infected live animals, may fly only under a State exemption or a State-of-Origin approval where the Instructions allow one. And at the top sit the articles and substances identified by name or generic description as forbidden under any circumstances, which shall not be carried on any aircraft: for some cargo, no packaging, quantity or paperwork makes the risk acceptable, and the system's answer is simply no.
Excepted by design
One family of dangerous goods flies outside the whole regime: articles and substances which would otherwise be classed as dangerous goods but which are required to be aboard the aircraft in accordance with the airworthiness requirements and operating regulations, or for the specialised purposes the Instructions identify, are excepted from the Annex's provisions. The fire extinguishers, oxygen bottles, batteries and flares the equipment module's lessons spent pages requiring are all, chemically, dangerous goods; so are the medical oxygen and equipment required for use during aeromedical flights. The exception has edges: replacements for such items, or removed items being shipped, travel as cargo under the Annex except as the Instructions permit, and the items passengers and crew may carry are excepted only to the extent the Instructions specify in their Part 8.
From acceptance to the hold
The carriage pipeline starts at the acceptance desk. An operator shall not accept dangerous goods for transport unless they are accompanied by a completed dangerous goods transport document, except where the Instructions say one is not required, and not until the package, overpack or freight container has been inspected per the Instructions' acceptance procedures, worked through an acceptance checklist. Behind the desk stands the packing law: packagings shall be of good quality, constructed and securely closed to prevent leakage in normal transport conditions, against changes of temperature, humidity and pressure and against vibration; suitable for and resistant to their contents; built and tested to the Instructions' specifications, which is why packing must comply with them: an aircraft cannot pull over, so the packaging is the containment for the whole flight. The inspections then bracket the flight, the operator's procedures covering inspection for damage, leakage or contamination: the check before loading keeps a failing package out of the air where it would become the previous lesson's in-flight emergency, the check after unloading catches what the flight did, and found contamination is removed, the radioactive case grounding the aircraft as the previous lesson taught. Some entries carry one more restriction: packages bearing the Cargo aircraft only label, loaded as the Instructions provide, for goods whose hazards or quantities are acceptable only where no passengers are carried.