071 Operational Procedures topic guide
Dangerous Goods: What Pilots Must Know
Dangerous goods questions are less about memorising a list and more about understanding a classification system built to answer one question consistently: what happens if this substance or article is involved in a fire, a leak, or an impact. Every article or substance that might be carried by air is sorted into one of nine hazard classes, and each class exists because the items in it fail in a particular, predictable way.
For the flight crew, the practical side of the syllabus is not the chemistry, it is the operating discipline built around that classification: what the commander must be told before departure, what passengers may or may not carry without realising it is dangerous goods at all, and what to do if something goes wrong once the aeroplane is airborne. Getting the system right, rather than the exact class number for one substance, is what carries across every exam variant.
Why the classification exists
The nine-class system groups dangerous goods by the nature of the hazard: things that explode, gases under pressure, flammable liquids and solids, substances that react or oxidise, toxic and infectious substances, radioactive material, corrosives, and a final class for miscellaneous items that are dangerous in air transport for reasons that do not fit the other eight, such as items that are only hazardous because of the pressure or temperature changes of flight. Rather than memorising every entry, it is more useful to understand that the class drives everything downstream: how the item must be packaged, how it must be labelled, where on the aeroplane it may be stowed, and whether it can be carried at all.
Some articles and substances are forbidden from air transport altogether, and others are permitted only as cargo, under specific packaging and quantity limits, and never in the cabin or as checked or carry-on baggage. This is not an arbitrary restriction: it reflects that certain failure modes, an uncontrolled fire from a reactive substance, for instance, are judged unacceptable to have anywhere on a pressurised aircraft in flight, however well packaged.
- Class 1: explosives
- Class 2: gases
- Class 3: flammable liquids
- Class 4: flammable solids and related hazards
- Class 5: oxidising substances and organic peroxides
- Class 6: toxic and infectious substances
- Class 7: radioactive material
- Class 8: corrosives
- Class 9: miscellaneous dangerous goods
Hidden dangerous goods and the commander's picture
A significant share of dangerous goods incidents involve items passengers do not think of as dangerous goods at all: spare lithium batteries loose in a bag, a camping stove with fuel residue, aerosols, or a cracked smoke detector packed in checked luggage. Because these items enter the system without a shipper's declaration, the defence against them is passenger awareness at check-in and a crew alert to the recognisable signs of an undeclared item causing a problem in flight, such as smoke, heat, or an unusual smell from a specific piece of luggage or cargo.
For declared dangerous goods carried as cargo, the commander must be given, before departure, a clear written notification of what is on board, in what quantity, and where it is stowed. This document, the notification to captain, lets the crew make an informed decision about accepting the load and gives them the exact information they would need in an emergency, since the correct firefighting or containment response can depend entirely on which class of goods is involved and where it sits on the aeroplane.
If an in-flight incident is suspected to involve dangerous goods, the general response follows the same logic as any onboard fire or contamination: identify the location and, if possible, the class of material involved, use the appropriate extinguishing agent for that class of hazard rather than assuming water or a generic extinguisher will always work, isolate the area if practicable, and consider whether the safest course is a diversion to the nearest suitable aerodrome rather than continuing to the original destination.
Worked example
Worked example: an undeclared item in the cabin
Not quite. The correct answer is B.
Correct answer: B
- A. The absence of a declaration does not mean the absence of a hazard. Many dangerous goods incidents involve undeclared items exactly like a passenger's own bag, and heat with a chemical smell is itself a recognised warning sign.
- B. Correct: heat and a chemical smell from a specific bag are recognised signs of a hidden dangerous goods problem, most often a battery, and the response is to locate, isolate if safe to do so, and keep diversion open rather than assuming it will resolve on its own.
- C. The notification to captain covers declared cargo, not an undeclared item a passenger has brought into the cabin. Its absence from that document does not clear this report.
- D. Moving a suspected heat or fire source into an inaccessible cargo hold removes the crew's ability to monitor or fight it further, which is the opposite of the intended isolation response.
Step by step
- Recognise the cues: heat and a chemical smell from one specific bag are classic signs of an undeclared dangerous goods problem, most often a damaged or shorting battery.
- Do not rely on the absence of a declaration; undeclared items are the more common real-world source of this exact scenario.
- Direct cabin crew to locate and, if it can be done safely, isolate the item using onboard procedures and equipment intended for this kind of event.
- Keep a diversion option live and reassess continuously; if the situation does not stabilise, diverting to the nearest suitable aerodrome takes priority over reaching the original destination.
Common mistakes
Assuming dangerous goods only means declared cargo
Passenger baggage regularly contains undeclared dangerous goods such as spare batteries or aerosols, and exam scenarios frequently test whether the student recognises this source rather than only the cargo manifest.
Treating all nine classes as needing the same response
The correct action, and often the correct extinguishing agent, depends on which class of hazard is actually involved. Answering generically instead of by hazard type is a common way to lose a mark on an otherwise simple scenario.
Forgetting that the notification to captain only covers what was declared
A clean notification to captain does not rule out an in-flight dangerous goods event caused by an undeclared item, and treating the document as a complete guarantee is a misreading of what it actually certifies.
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Last reviewed July 2026