Operational Procedures

Fire, Smoke and Decompression - ATPL 070 — Operational Procedures | Pilot Assessment Training

Fire, Smoke and Decompression

Emergencies on Board · Lesson 1 of 2•13 min read

Two enemies share this lesson: fire and the loss of the cabin's pressure. For both, the systems course built the machinery, the detection loops and bottles, the outflow valve and its controller, and the equipment module of this course priced what must be carried. What is left is the crew's half: which agent on which fire, how to apply it, what the smoke and decompression drills look like, and why they must be known before they are needed.

Fires at their types

The syllabus opens with two engine-fire cases and one deliberately repeated lesson about both. A carburettor fire, the piston world's induction fire, and an engine fire proper each have a drill, and in both cases the actions to be taken may be type-specific and should be known by the pilot. That sentence is the learning objective itself, and it carries the operational point: the flight manual's fire drill is memory-item material, learned on the type, because the differences between types are exactly where a generic drill kills. One type's carburettor-fire drill may want the fuel kept flowing to burn through what is in the induction tract; another wants it cut at once; the only universal is that the pilot knows the type's own answer before the fire. The engine-fire shape the systems course's fixed bottles serve, shutting the engine down and firing the extinguishant into the nacelle, is likewise flown exactly as the type manual sequences it.

Choosing the extinguisher

Hand-extinguisher choice starts with the fire classification the certification world uses. Class A is ordinary combustibles: wood, cloth, paper, rubber, plastics. Class B is flammable liquids: fuels, oils, greases, solvents. Class C is energised electrical equipment, where a non-conductive agent matters. Class D is combustible metals such as magnesium, titanium, sodium and lithium, and one modern trap sits beside it: a fire in a passenger's laptop or phone, a small number of lithium batteries, is not treated as a Class D fire.

The agents then map onto the classes. Water answers Class A, cooling the material below ignition and soaking it against re-ignition. Carbon dioxide blankets Class B and C fires. Dry chemical covers A, B and C, but only the mono-ammonium phosphate powder earns the all-purpose rating. Halon and its clean-agent replacements cover Class A, B and C fires and must never be used on Class D, where the agent can react violently with the burning metal, a prohibition water shares. Specialised dry powder is the Class D answer and nothing else's. The guidance then subtracts the cabin cases: carbon dioxide, dry chemical and specialised dry powder are not recommended as handheld agents inside the aircraft, dry chemical for the reasons the equipment module taught, obscured vision and residue in the electronics. That leaves halon and its replacements as the cabin's working agent, and the flight deck's own extinguisher suitable for Class B and Class C fires, with the halons themselves unacceptable in new installations whose certification application came after the end of 2014, replaced by the clean agents. The same logic covers the rest of the aircraft: the units the equipment module placed in the galleys off the main deck and available for each accessible cargo compartment carry the same working agents, and the cabin's extinguishers are located with the lavatories and galleys in mind, so that the compartments where fires start have an extinguisher within reach.

Check you understood

Three questions from this lesson — one straightforward, one that applies it, one that pushes a little further. Nothing is recorded, and you can draw a new set as often as you like.

1. Warm-up
Which signs identify a rapid or explosive decompression?
2. Applying it
Which set of precautions applies when using a hand fire extinguisher in flight?
3. Pushing it
How do steel and carbon brakes differ in absorbing the energy of a rejected take-off?

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Applying it

The application guidance is one long argument for speed. An on-board fire grows with time, so the guidance wants it attacked immediately and aggressively: beside an unextinguished in-flight fire, the toxicity of the agent is the smaller risk. The technique: attack the base of the fire at its near edge, sweeping side to side toward the back, and avoid a close-range first burst where burning material might splatter. Around the attack sit the housekeeping steps: recirculation fans off as the flight manual permits, because the halocarbon agents are heavier than air and the outflow valves can then carry them overboard; protective breathing equipment on where the agent or the smoke demands it, the same PBE the equipment module priced; and once the fire is confidently out, ventilate the compartment, staying alert, because fresh airflow can feed anything still smouldering. The lithium-battery fire gets its own drill: knock it down with halon, a halon replacement or water, then pour water over the cells to cool them and stop the fire propagating cell to cell, and never move the burning device into a burn bag. The carriage rule stands behind all of it: the agent's type and quantity shall suit the compartment's likely fire and minimise toxic gas concentration where people sit.

Smoke drills

Smoke gets the same type-specific sentence as the engine fires, and for the same reason: the actions in the event of smoke in the flight crew compartment or the cabin may be type-specific and should be known by the pilot. The shape is common enough to state: protect the crew first, oxygen masks and goggles or PBE so the people fighting the problem stay conscious and seeing; identify and isolate the source, which on most types means working the air-conditioning and electrical systems per the type's smoke drill; and treat smoke that cannot be cleared as the emergency it is, with descent and landing on the table. But which pack to close first, which bus to shed, whether to depressurise a stubborn smoke-filled cabin: those answers differ type to type, live in the type's procedures, and must be known before the flight deck fills with the reason to use them.

What happened in the pastSwissair Flight 111 — off Peggy's Cove, 2 September 1998

Less than an hour out of New York for Geneva on 2 September 1998, the pilots of a Swissair MD-11 noticed an unusual smell in the cockpit. Two and a half minutes later they could see smoke; a minute after that they called PAN PAN and asked for a diversion, settling on Halifax. Above the cockpit ceiling, in a space with no smoke detector and no extinguisher, an electrical arc had ignited the metallised covering of the insulation blankets — a material that had passed the certification flammability test of its day and burned readily in service, and whose history of ground fires was already known to the manufacturer without any regulator having ordered its removal.

The crew flew the drill this section describes as it was written at the time. They worked the smoke checklist, which could take twenty to thirty minutes and placed landing preparation at its end; they decided to dump fuel; they had the cabin readied. Ten minutes after the smell the fire was degrading systems; at fourteen the autopilot dropped out and an emergency was declared; at fifteen the recorders stopped. The aircraft struck the sea 20 minutes and 40 seconds after the first smell. All 229 aboard died. The investigation's most sobering finding is the one a reader expects least: it calculated that even a flawless emergency descent begun at the moment of the PAN PAN call would have reached Halifax after the fire had taken the systems needed to land, and that from any point after the initial odour the time to complete an approach exceeded the time the cockpit had left.

The causes were set out around the material, not the crew: certification standards that allowed flammable insulation, no detection or suppression where the fire started, no integrated in-flight firefighting plan, and a checklist that de-emphasised preparing to land. What changed followed the Board's recommendations: the flammable blankets were ordered out of the fleets, a stricter radiant-panel flammability test replaced the old one, wiring inspections and practices were overhauled, and the doctrine this section now teaches was written — treat smoke that cannot be cleared as the emergency it is, and give attention without delay to landing at the nearest suitable airport, because the clock the crew cannot see is the only one that counts.

Hot brakes

A heavy-weight landing or a rejected take-off pours the aircraft's kinetic energy into the brake stacks, and the systems course taught what follows: the brake energy and cooling tables that gate how soon the next departure may follow, the fade that can rob an overheated brake exactly when it is needed again, the leaked fluid or grease that hot brakes can ignite, and the thermal fuse plugs that melt at a set temperature and deflate the tyres deliberately before heat can burst them. The operational consequences follow directly: after a hot stop the crew respects the cooling time before taxiing back for another departure, and treats the wheels as a burst hazard whose neighbourhood the ground crew should not casually share. The steel-versus-carbon difference the brakes lesson taught carries into the emergency: carbon keeps its friction as it heats where hot steel fades, and carbon wears by the number of applications rather than the energy of each, so the two materials reach a rejected take-off with different margins and different tempers.

Losing the cabin slowly

The pressurisation lesson built the machine; this section fails it gently. A slow decompression comes from a leaking door or window seal, a valve that has crept open, or a pressurisation controller failure that stops flying the cabin. Its danger is its quietness: detection is the instruments, the cabin altitude and differential creeping the wrong way, the cabin rate showing a climb nobody commanded, ears popping, and, if it runs long enough unnoticed, the cabin altitude warning above 10,000 ft that the systems course taught, on many types the same horn as the take-off configuration warning. The actions: oxygen masks on when the cabin altitude demands it, then work the failure per the type, which for a failed controller means the manual pressurisation mode, the crew driving the outflow valve by hand, and where the cabin cannot be held, a descent to an altitude where the cabin can breathe, flown per the type's drill.

Losing the cabin fast

A rapid or explosive decompression is a structural event: a failed window, a door, a breach of the pressure vessel large enough to dump the differential in seconds or less. Detection is unmistakable: a bang, instant fog as the cabin's moisture condenses, dust and loose objects flying toward the breach, wind noise, a sudden cold, and ears hammered by the pressure change. The drill is the memory-item sequence the pressurisation lesson previewed: oxygen masks on immediately, crew communication established, and an emergency descent flown as the type prescribes toward an altitude where the occupants can live without the masks, the level chosen against terrain and the minimum safe altitudes the flight planned.

The effects on the occupants divide by tempo. The slow decompression's threat is insidious hypoxia: the cabin climbs quietly, judgement degrades before anyone feels ill, and the ear and sinus discomfort that accompanies the pressure change is the body's only routine warning. The rapid decompression trades stealth for violence: at high cabin altitudes useful consciousness is measured in moments, which is why the masks come first and immediately; around the hypoxia sit the fog, the cold, the noise, flying debris near the breach, and the barotrauma of ears and sinuses asked to equalise a huge change at once. Either way the lesson is the same one the whole chapter teaches: the drill is decided and learned before the event, because the event lends no time.

Fire, smoke and decompression, memorised

Carburettor fire, engine fire, smoke: the actions may be type-specific and should be known by the pilot; the type manual's drill is memory-item material, learned before it is needed.
Fire classes: A ordinary combustibles, B flammable liquids, C energised electrical equipment, D combustible metals; a small number of lithium batteries is not a Class D fire.
Agents: water for A; carbon dioxide for B and C; dry chemical A to C (mono-ammonium phosphate the only all-purpose powder); halon and clean agents A to C and never on D, a never water shares; specialised dry powder for D only; CO2, dry chemical and dry powder not recommended handheld in the aircraft; flight deck unit suitable for B and C.
Applying: attack immediately and aggressively at the base, near edge, sweeping side to side; no close-range burst onto splashing material; recirculation off as the manual permits; PBE where needed; ventilate once out, alert for smoulder; lithium fires: knock down with halon or water, then pour water to cool the cells, never a burn bag; agent type and quantity shall suit the compartment and minimise toxic gas where people sit.
Hot brakes after a heavy landing or rejected take-off: cooling tables gate the next departure, fade and fluid ignition threaten, fuse plugs deflate tyres deliberately, ground crew keep clear; carbon holds friction hot and wears by applications, steel fades hot and wears by energy.
Slow decompression: seal or valve leaks or a controller failure; detected on the cabin altitude, differential and rate, ears, then the 10,000 ft warning; masks when the cabin demands, manual mode for a dead controller, descend if the cabin cannot be held.
Rapid or explosive decompression: structural failure of window, door or pressure vessel; bang, fog, flying debris, wind, cold, ears; masks on immediately, crew communication, emergency descent per the type.
Occupant effects: slow means insidious hypoxia with quiet judgement decay and ear or sinus discomfort; rapid means moments of useful consciousness at high cabin altitude, fog, cold, debris and barotrauma; masks first, always.