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|Category:||Fire Smoke and Fumes|
Electrical fires on aircraft originate from electrical components. An immident electrical fire often can be detected by indirect indications or alarm-system sensors before the fire ignites. It is also possible that electrical fires will remain hidden to the flight crew or cabin crew for a prolonged time. in those situations, the electrical fire may become apparent too late for crewmembers to take action to eliminate the threat.
Because modern commercial transport aircraft typically contain miles of wire inside electrical cables, looms and wiring harnesses (most of them in hard to reach places) the most frequent cause of electrical fires is some type of insulation issue, such as:
- Worn insulation — Mainly due to ageing and exposure heat, worn insulation may be more susceptible to catching fire from overheating; worn insulation also may fall off wires, exposing the metal conductor to short-circuiting risks;
- Torn insulation — Tearing is typically due to improper cable installation that may lead to the cable being repeatedly under mechanical stress, ultimately resulting in the conductive metal being exposed;
- Contaminated insulation — When soaked with oil from any source, insulation is also more likely to catch fire (e.g. from electrical overheating); and,
- Breaks in insulation — Exposed metal conductors (wires touching) inside cables may result in a short circuit or an electrical arc or spark.
Imminent or smouldering/burning electrical fires may be indicated directly or indirectly by the following clues:
- Over-voltage warning
- Higher than normal electrical load
- Popped circuit breaker
- white smoke and acrid smell of hot or burning insulation; note, however, that these clues may also be caused by cable/wiring insulation being burned by some other type of fire.
Defences and Best Practices
Prevention is the best countermeasure against electrical fires, including these actions:
- Proper aircraft maintenance - Cables should be checked for signs of ageing or damage at regular intervals and replaced as necessary.
- Lead acid storage batteries containment — These batteries must be contained in an approved battery box with the lid vented to the outside of the aircraft to prevent explosive hydrogen gas from entering the aircraft.
- Electrical component replacement — When replacing electical equipment (e.g. light bulbs), only regulator-approved components should be used. Also, the maintenance engineering should make sure the new component fixture is complete and intact.
- Pre-flight inspection — A thorough inspection may reveal evidence (e.g., by sight or smell) of leaked fuel, oil, or hydraulic fluids.
When an in-flight electrical fire is suspected or indicated, common flight crew responses consider:
- Emergency landing — Landing immediately at the nearest suitable aerodrome — per international best practices — is usually the best course of action if a fire is suspected, even if there are no visible flames.
- Fire characteristics — Once ignited, electrical fires burn just like most any aircraft fire. One difference is that the heat from the energized electrical wiring or component that ignited the fire might sustain it by continued ignitition. Therefore, the common first step when electrical fire is suspected is to cut the power by turning off the master switch. This removes the ignition source, and if an imminent fire has not started to burn, may lead to elimination of ignition threat.
- Troubleshooting — If electrical power is essential for the flight, some emergency checklists authorize the flight crew to attempt to identify and isolate the faulty circuit by:
- Turning all individual electrical switches OFF.
- Turning the master switch back ON.
- Selecting electrical switches that were ON before the fire indication, one at a time, permitting a short time lapse after each switch is turned ON to check for signs of odor from fumes, smoke or sparks.
(Note that this procedure may have the effect of recreating the original problem. On the other hand, lack of electrical power would require a no-flap landing, manually lowering the landing gear, no normal communication capability and no navigation capability, which could increase risk factors, especially if flying at night or instrument meteorological conditions. See Further Reading below for current best practices in designing emergency checklists for smoke-fire-fumes events.)
- Deploying extinguishers — If flames from an electrical fire have already started, cutting the power supply will not be enough, and immediate use of some sort of extinguishing equipment will be necessary. The crew's initial focus should be on aggressively extinguishing the fire with a readily available extinguisher. Water must not be used if the crew believes the fire is of electrical origin.
- Declaring MAYDAY — If time permits, the flight crew should communicate with air traffic control (ATC) before powering down the electrical system for the following reasons:
- Declaring an emergency will inform ATC that there is a potentially life-threatening so that ATC will be able to provide direct assistance to the flight crew, or advise the search and rescue (SAR) authorities in case of a forced landing, and alert the aerodrome's rescue firefighting (RFF) authorities to prepare for all landing contingencies.
- By setting secondary surveillance radar (SSR) transponder code 7700, the flight crew will also draw the attention of ATC.
- Position-reporting beacon — By activating the emergency locator transmitter (ELT), which has its own self-contained power supply, the flight crew automatically will help guide the SAR teams to the location of a forced landing, should that become necessary.
- Portable NAV/COM — On smaller aircraft, carrying a handheld radio transceiver, with integrated or separate handheld GPS navigation can be very helpful if the aircraft electrical system needs to remain off for optimal safety.
- Evacuating smoke/fumes — Managing the smoke is another important part of dealing with an electrical fire. There is no universal solution. Venting the smoke may improve breathing and vision, but the process may also feed the flames oxygen. If the latter situation happens, the flight crew's best option is to close the vents. Current best practices for aircraft operators to update smoke-fire-fumes checklists on their fleets, as noted, also address the mitigation of toxic fumes.
Accidents and Incidents
Fire - Electrical Origin
- A319, London Heathrow UK, 2009 (On 15 March 2009, an Airbus A319-100 being operated by British Airways on a scheduled passenger flight from London Heathrow to Edinburgh experienced an electrical malfunction which blanked the EFIS displays following engine start with some electrical fumes but no smoke. The engines were shut down, a PAN was declared to ATC and the aircraft was towed back onto the gate where passengers disembarked normally via the airbridge.)
- A388, en-route, north east of Singapore, 2011 (On 31 January 2011, a Singapore Airlines Airbus A380-800 was in the cruise when there was sudden loud noise and signs of associated electrical smoke and potential burning in a toilet compartment with a corresponding ECAM smoke alert. After a fire extinguisher had been discharged into the apparent source, there were no further signs of fire or smoke. Subsequent investigation found signs of burning below the toilet floor and it was concluded that excessive current caused by a short circuit which had resulted from a degraded cable had been the likely cause, with over current protection limiting the damage caused by overheating.)
- AS55, vicinity Fairview Alberta Canada, 1999 (On 28th April 1999, an AS-355 helicopter suffered an in-flight fire attributed to an electrical fault which had originated from a prior maintenance error undetected during incomplete pre-flight inspections. The aircraft carried out an immediate landing allowing evacuation before the aircraft was destroyed by an intense fire.)
- AT43, vicinity Geneva Switzerland, 2006 (On 29 March 2006 at about 1 mile from touchdown when in VMC on a night approach to destination Geneva, an ATR 42-300 being operated by Farnair on a cargo flight experienced a sudden electrical fire in the flight deck and an emergency was declared to ATC. Despite this situation the aircraft was able to land normally and vacate the runway via an RET after which it was forced to stop.)
- B762, San Francisco CA USA, 2008 (On 28 June 2008 a Boeing 767-200 being operated as a Public Transport cargo flight by ABX Air (DHL) experienced a ground fire after loading had been completed and all doors closed and just before engine startup at night. The fire was located in the supernumerary compartment of the airplane. This compartment, which is present on some cargo airplanes, is located directly aft of the cockpit and forward of the main deck cargo compartment which is where the toilet, galley, and three non-flight crew seats are located (see diagram below).The flight crew evacuated the aircraft through the flight deck windows and were not injured, but the aircraft was substantially fire damaged and later classified as a hull loss.)
- B763, Manchester UK, 1998 (On 25th November 1998, baggage containers on a B767, moved in flight causing damage to a cabin floor beam and damage to the standby system power supply cable causing electrical arcing. The aircraft landed safely at Manchester, UK, and the damage was only discovered during unloading.)
- B772, Cairo Egypt, 2011 (On 29 July 2011 an oxygen-fed fire started in the flight deck of an Egypt Air Boeing 777-200 about to depart from Cairo with most passengers boarded. The fire rapidly took hold despite attempts at extinguishing it but all passengers were safely evacuated via the still-attached air bridge access to doors 1L and 2L. The flight deck and adjacent structure was severely damaged. The Investigation could not conclusively determine the cause of the fire but suspected that wiring damage attributable to inadequately secured cabling may have provided a source of ignition for an oxygen leak from the crew emergency supply)
- B772, London Heathrow UK, 2007 (On 26 February 2007, a Boeing 777-222 operated by United Airlines, after pushback from the stand at London Heathrow Airport, experienced internal failure of an electrical component which subsequently led to under-floor fire. The aircraft returned to a stand where was attended by the Airfield Fire Service and the passengers were evacuated.)
- B788, Boston MA USA, 2013 (On 7 January 2013, a battery fire on a Japan Air Lines Boeing 787-8 began almost immediately after passengers and crew had left the aircraft after its arrival at Boston on a scheduled passenger flight from Tokyo Narita. The primary structure of the aircraft was undamaged. Investigation found that an internal short circuit within a cell of the APU lithium-ion battery had led to uncontained thermal runaway in the battery leading to the release of smoke and fire. The origin of the malfunction was attributed to system design deficiency and the failure of the type certification process to detect this.)
- B788, London Heathrow UK, 2013 (On 12 July 2013 an unoccupied and unpowered Boeing 787-8, remotely parked at London Heathrow after an arrival earlier the same day caught fire. An investigation found that the source of the fire was an uncontained thermal runaway in the lithium-metal battery within an Emergency Locator Transmitter (ELT). Fifteen Safety Recommendations, all but one to the FAA, were made as a result of the Investigation.)
- DC93, en-route, Cincinnati OH USA, 1983 (On 2 June 1983, a DC9 aircraft operated by Air Canada was destroyed following an in-flight fire which began in one of the aircraft’s toilets. 23 passengers died in the accident.)
- DH8B, en route, southwest of Windsor Locks CT USA, 2015 (On 5 June 2015, a DHC8-200 descending towards Bradley experienced an in-flight fire which originated at a windshield terminal block. Attempts to extinguish the fire were unsuccessful with the electrical power still selected to the circuit. However, the fire eventually stopped and only smoke remained. An emergency evacuation was carried out after landing. The Investigation was unable to establish the way in which the malfunction that caused the fire arose but noted the continuing occurrence of similar events on the aircraft type and five Safety Recommendations were made to Bombardier to address the continuing risk.)
- AT76, en-route, east of Cork Ireland, 2016 (On 24 August 2016, an ATR 72-600 experienced a static inverter failure which resulted in smoke and fumes which were identifiably electrical. Oxygen masks were donned, a MAYDAY declared and after the appropriate procedures had been followed, the smoke / fumes ceased. The Investigation noted a long history of capacitor failures affecting this unit which continued to be addressed by successive non-mandatory upgrades including another after this event. However, it was also found that there was no guidance on the re-instatement of systems disabled during the initial response to such events, in particular the total loss of AC electrical power.)
- B744, Phoenix USA, 2009 (On 10 January 2009, a Boeing 747-400 being operated by British Airways on a scheduled passenger flight from Phoenix USA to London had been pushed back from the gate in normal daylight visibility and the engines start was continuing when fumes and smoke were observed in the cabin and flight deck. The aircraft commander decided to return to the stand but there was some delay while the tug was reconnected and the movement accomplished. The intensity of the fumes increased and as the aircraft came to a halt on the stand an emergency evacuation was ordered.)
- B763, Frankfurt Germany, 2007 (On 20 August 2007, at Frankfurt, while a Boeing 767-300 was taxiing to its parking position, thick smoke developed in the passenger cabin. All passengers and the crew were able to leave the aircraft at the gate without further incident.)
- B763, en-route, Northern France, 1998 (On 9 January 1998, a Boeing 767-300 operated by United Airlines experienced an electrical systems malfunction subsequently attributed to arcing in a faulty electrical loom. The crew elected to divert to London Heathrow where emergency evacuation was carried out on a taxiway upon landing.)
- B788, en-route Shikoku Island Japan, 2013 (On 16 January 2013, a main battery failure alert message accompanied by a burning smell in the flight deck was annunciated as an ANA Boeing 787-8 climbed through FL320 on a domestic flight. A diversion was immediately initiated and an emergency declared. A landing at Takamatsu was made 20 minutes later and an emergency evacuation completed. The Investigation found that the battery had been destroyed when thermal runway followed a suspected internal short circuit in one of the battery cells and concluded that certification had underestimated the potential consequences of such a single cell failure.)
- E170, Nuremberg Germany, 2013 (On 13 March 2013, smoke and fumes were immediately evident when the cable of an external GPU was connected to an ERJ170 aircraft on arrival after flight with passengers still on board. A precautionary rapid disembarkation was conducted. The Investigation found that a short circuit had caused extensive heat damage to the internal part of the aircraft GPU receptacle and minor damage to the surrounding structure and that the short circuit had occurred due to metallic FOD lodged within the external connecting box of aircraft GPU receptacle.)
- Fire in the Air
- In-Flight Fire: Guidance for Flight Crews
- Passenger Cabin Fire
- Checklists and Procedures for Non-Alerted Fire/Smoke/Fume Events
- FAA Advisory Circular (AC) 120-80A “In Flight Fires,” Dec. 22, 2014.
- FAA AC 25-16: "Electrical Fault and Fire Prevention and Protection," April 5, 1991.
- "In-Flight Electrical Fires," Safety Brief, SB08-04/09, AOPA Air Safety Foundation, 2009.
- "Smoke, Fire and Fumes in Transport Aircraft: Past History, Current Risk and Recommended Mitigations," Second Edition 2013. Royal Aeronautical Society.