In-Flight Fire, Smoke and Fumes

Fire is the emergency that leaves least time. On the ground the occupants can escape a fire by evacuating; in flight it has to be contained until the aircraft is on the ground, which may be many minutes away. The crew's work therefore runs on three tracks at once: protect the people fighting it, find and isolate the source, and get the aircraft down.

Smoke and fumes are usually the first sign, and they are a hazard in their own right. They can incapacitate the crew, hide the instruments and fill the cabin long before any flame is seen. Two accidents are often quoted in training: Swissair Flight 111 in 1998, where a fire spread unseen above the flight deck ceiling, and ValuJet Flight 592 in 1996, where undeclared chemical oxygen generators burned in the cargo hold. The lesson drawn from both is the same: once a fire is suspected, preparing to land comes first.

Fire classes

Combustion needs three things, fuel, oxygen and heat, known as the fire triangle. Removing any one puts the fire out: shutting off the fuel deals with an engine fire, smothering removes oxygen, and cooling agents remove heat. Halons do something more, interrupting the chemistry of the flame itself.

Extinguishers are chosen for the kind of fire likely at each location. FAA guidance on hand extinguishers (AC 20-42D) uses the US fire classes:

The European standard EN 2 letters the classes differently: its Class C is flammable gases, and electrical fires have no class of their own. The pictograms on the extinguisher label are therefore the safer guide.

Smoke, fire and fumes procedure

Every transport type has a smoke, fire and fumes procedure, with memory items or a quick reference checklist and a separate paper procedure for events that the warning system cannot detect. The structure is broadly common:

1. Oxygen masks on, 100 per cent, with smoke goggles where separate, and crew communication established through the mask microphones.
2. Fly the aircraft. One pilot flies, using the autopilot if available; the other runs the procedure.
3. Declare the emergency and start the diversion. If the source cannot be found and isolated quickly, the aircraft is landed as soon as possible, and the approach is planned while the procedure continues.
4. Identify and isolate the source. The cabin crew report where the smoke is and what it looks and smells like; the flight crew check for system warnings and shed electrical or air conditioning sources in the order the checklist gives.
5. Fight any fire with the extinguishers available, then remove the smoke once the source is isolated.

Airbus, for example, names smoke as one of the few situations in which the crew may interrupt a procedure to reassess, because smoke can grow faster than a checklist can be read. The cabin crew are briefed early for a possible evacuation after landing.

Avionics and electrical smoke

Electrical fires are sustained by electrical power, so removing the power usually removes the cause, while an extinguisher only deals with the symptom. In a light aircraft the first action for acrid electrical smoke is therefore the master switch off. Vents are then used as the flight manual directs, the extinguisher is used if there are flames, and if electrical power is needed for the landing, essential items are restored one at a time so that the faulty circuit shows itself. Landing without electrics in visual conditions is acceptable.

Transport aircraft watch the equipment bay with smoke detectors in the ventilation ducts. On the A320, smoke detected for more than 5 seconds in the avionics extraction duct gives an AVIONICS SMOKE caution, a SMOKE light on the GEN 1 LINE pushbutton and FAULT lights on the ventilation BLOWER and EXTRACT pushbuttons. With both set to OVRD, cooling air comes from the air conditioning and is exhausted overboard. If the smoke persists, the procedure sets the smoke configuration, which sheds about 75 per cent of the electrical equipment and switches GEN 1 LINE off so that AC BUS 1 is fed from generator 2. The fuel pumps are connected upstream of the generator 1 line contactor so that the engines stay fed.

Cabin fires: galley, lavatory and seats

In the cabin the cabin crew are the fire fighters, typically working as a team: one fights the fire, another brings more extinguishers and protective equipment, and another keeps the flight deck informed. For a galley oven or other electrical appliance the logic of an electrical fire applies: its power is switched off first.

Lavatories are closed, unattended spaces where a fire can grow before anyone sees it. The fatal Air Canada Flight 797 lavatory fire in 1983, whose origin was never determined, led to two requirements for aircraft with 20 or more passenger seats: a smoke detector in each lavatory and an automatic extinguisher in each waste bin. The bin extinguisher is a small halon bottle whose fusible plug melts in a fire and releases the agent through a spray ring.

A deep-seated fire in seat foam or fabric may flare up again after halon has put the flames out, because halon does not cool. The drill is to follow up with water to cool the material right through and to keep the seat under observation for the rest of the flight.

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Lithium battery fires

Passengers carry many lithium batteries in phones, laptops and power banks (see dangerous goods). A damaged, crushed or faulty cell can enter thermal runaway, overheating and releasing flammable electrolyte, and the heat spreads to neighbouring cells, so a battery pack can reignite repeatedly after the flames are out.

FAA guidance for a lithium battery fire in a portable electronic device follows from this:

• use a halon, halon replacement or water extinguisher to put out the flames;
• then douse the device with water or another non-alcoholic liquid to cool it and stop further cells from running away;
• do not cover it or pack it in ice, which insulates it and makes further runaway more likely;
• do not pick up or move a device that is burning or smoking;
• keep it under observation until landing.

IATA guidance for operators adds that the electrical or mechanical controls of a seat must not be used to recover a device lost in it, because the mechanism can crush the battery. A lithium battery fire is reported to the flight deck at once, and the commander plans to land.

Smoke and fumes removal

Once the source has been isolated, the smoke still has to be cleared. Each type has its own smoke removal procedure, which may use maximum air conditioning flow, dedicated extraction, the pressurisation outflow valve, a descent, or emergency ram air ventilation. The procedure is applied as written, because improvised changes to air flow can drive smoke towards the flight deck instead of away from it. After halon has been used in a confined space, ventilation is increased to clear the agent and its decomposition products, which are harmful to breathe.

Fumes without visible smoke, such as oil or chemical smells from the air conditioning, follow the same logic: masks on if anyone is affected, isolate the likely source, and land if the fumes persist.

Fire extinguisher types

Portable fire extinguishers, also called hand-held fire extinguishers, are carried on the flight deck, in the cabin and in each galley not on the main deck. Transport aeroplanes also have fixed systems for engines, APU, cargo holds and lavatory bins (see engine failure and engine fire).

Under EASA rules the number of cabin hand fire extinguishers grows with the seats: one for 7 to 30 passenger seats, two for 31 to 60, three for 61 to 200, four for 201 to 300, and one more for each further 100 up to eight for over 600. At least one extinguisher in a cabin of 31 to 60 seats, and at least two above 60, must contain Halon 1211 or an equivalent agent, and at least one halon or equivalent extinguisher is kept on the flight deck. The US rule, 14 CFR 121.309, uses the same scale.

PBE and portable emergency equipment

Protective breathing equipment (PBE), often a smoke hood, lets a crew member work in smoke. It must protect the eyes, nose and mouth and supply oxygen for at least 15 minutes, from the aircraft's supply or its own chemical generator. It is required on pressurised aeroplanes and on unpressurised aeroplanes of more than 5,700 kg or more than 19 passenger seats: at each flight crew station, near each cabin crew station, and portable units beside the hand extinguishers. A chemical hood cannot be stopped once started, and the wearer notices the supply running out as increasing resistance to breathing. Crews practise with it in recurrent training, which includes actual fire fighting and exercises in a smoke-filled environment at least every three years.

A crash axe or crowbar must be carried on the flight deck of aeroplanes with a maximum take-off mass above 5,700 kg or more than 9 passenger seats, and above 200 seats a second one in or near the rearmost galley. Any stowed in the cabin must be out of sight of passengers. It is used to reach a fire behind panels or linings and to force jammed exits.

Other portable emergency equipment supports the fire fight and the evacuation that may follow: portable oxygen bottles, torches, fire-resistant gloves where fitted, and megaphones, one for 61 to 99 passenger seats and two for 100 or more. The fixed detection and extinguishing systems of holds and lavatories are covered in cargo and lavatory fire protection.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.