Last Updated: 24 September 2007
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Introduction
Most jet transport aircraft are very poorly designed with regard to the protection, detection and effective handling of in-flight electrical fires, as the Swissair Flight 111 crash off Nova Scotia on 2nd September 1998 tragically demonstrated. 1
This situation is exacerbated by the widespread use in aircraft of a potentially dangerous electrical wire product called 'KAPTON' 2 and the fact that the current generation of airline jet transport aircraft (i.e. Airbus A320, A330, A340 and Boeing B777 and MD11) cannot be effectively flown without electricity, unlike earlier generation passenger jets such as the DC9.
Inflight electrical fire is not a rare event. According to Captain Jim Shaw, manager of the inflight fire project for the United States Air Line Pilots Association (ALPA), there are on average three (3) fire and smoke events in jet transport aircraft each day in USA and Canada alone, and the vast majority are electrical. (SOURCE: Air Safety Week 24 April 2000) According to Air Safety Week, "aircraft are making emergency landings, suffering fire damage to the point of being written off etc, at the rate of more than one a month based on the experience of the past few months". (SOURCE: Air Safety Week 19 March 2001) 3
Inflight electrical fire is an issue that has to a large extent been ignored by all sections of the aviation industry. This document discusses a number strategies to address this issue.
Readers are invited to agree with, disagree with, or seek clarification about any of the material listed below, or make suggestions about any aspects of aircraft design they think should be included in any future updates of this article.
Alex Paterson (May 2001)
For a fire to occur, three (3) things need to be present - those being fuel, oxygen and a source of heat to initiate the process. (i.e. an ignition source) Removal of any one of these three items renders the fire unsustainable and it goes out. With regard to aircraft electrical systems, the 'fuel' for an electrical fire can consist of the actual wiring insulation itself, acoustic insulation material such as Mylar surrounding electrical wire amongst other things, dust and debris which has settled around wire (especially dust contaminated with oil and hydraulic fluid, both of which are flammable) and the high quantity of plastic products installed throughout aircraft. The ignition source for an electrical fire is the electrical current itself, usually associated with the breakdown of a wire's insulation leading to a short circuit - hence the term 'electrical fire'.
Obviously, once an electrical fire starts removal of the electric current from the damaged electrical wire is vital in order to remove the primary source of heat generation and begin suppressing the fire. However, incredible though it may sound, current jet transport aircraft are not designed with a specific strategy to remove the electricity from damaged circuits, as evidenced by the current Boeing Electrical Fire drill which simply instructs pilots to "remove electrical power if the fire source can be determined" - a procedure that is virtually impossible to carry out in a real life inflight electrical fire situation due to the fact that a major electrical fire would almost certainly involve the damage and electrical arcing of literally dozens, if not hundreds of wires. The situation is further exacerbated by the fact that the current generation of 'computerised' jet aircraft cannot be effectively flown without electricity, which means the total removal of electricity from a modern computerised jet is not an option. 4
In summary, an electrical fire cannot be successfully suppressed and put out unless the electric current feeding it is removed from the damaged electrical circuits, yet present aircraft electrical fire drills do not attempt to do this in a systematic or effective manner.
However, a simple foolproof method to remove electrical current from damaged wire circuits is available through the concept of a Virgin Electrical Bus.
The "Virgin Electrical Bus" proposal is essentially the installation in aircraft of a completely separate emergency electrical wiring system which would only be used in the event of an in-flight electrical fire to power essential aircraft systems normally available under Standby Electrical power to get the aircraft back on the ground in one piece.
In normal operation, the Virgin Electrical wiring system would remain unpowered.
In the event of a suspected electrical fire, the aircrew would simply pull a suitably located (and ideally, illuminated) 'ELECTRICAL FIRE' Handle (a one item drill) which would do the following things:
Clearly the Virgin Bus proposal needs much design work to take into account numerous engineering considerations such as:
Other design initiatives to reduce the risk of inflight electrical fire include:
and their replacement with non-flammable alternatives.
No Jet Transport Aircraft complies with FAR 25
Regulations pertaining with system redundancy.
Failure of aircraft electrical wiring associated with a major electrical fire was never given proper consideration in the design of aircraft as evidenced by the fact that all transport aircraft currently flying contain wiring looms comprising literally hundreds of wires made up of different wire types from various electrical sources (and of different voltages) carrying electrical current to a myriad of unrelated aircraft systems. As a consequence, no jet transport aircraft currently flying or in production complies with the US Federal Aviation Regulation (FAR 25) or the equivalent European Joint Aircraft Regulation (JAR 25) pertaining to electrical system redundancy in the event of a total wire loom failure associated with an electrical fire or explosive arc tracking event . 7
No Jet Transport Aircraft has an effective strategy in place to fight
electrical fire
as evidenced by the current Boeing B777 electrical fire drill which
simply instructs aircrew to "Remove Power" from the effected circuit
without providing them with any instructions as to how they should
actually identify the affected circuits or remove power from the
same. As a minimum requirement, an aircraft electrical fire drill
should instruct aircrew to immediately configure the aircraft on
Standby Electrical Power in order to remove as much electricity from
the aircraft electrical system as possible.
8
COMMENT: In Australia we have a non alcoholic drink called 'Claytons'
TM , which is advertised by its manufacturers as "the
drink you have when you're not having a drink". In the author's
opinion, the Boeing Electrical Fire drill is a 'Claytons' emergency
drill - the drill you have when you don't have a proper strategy in
place to deal with a situation.
Any electrical fire drill that requires aircrew to trouble shoot the problem by applying power to electrical circuits in an endeavour to isolate the problem (e.g. MD11 electrical fire drill) is a potential death trap (as evidenced by the Swissair Flight SR111 tragedy) and should be changed as a matter of urgency.
Airline pilots should consider the operational ramifications of removing all electrical power from their aircraft as a possible strategy to deal with an inflight electrical fire. This strategy is certainly a viable option in older generation jets such as the DC9, MD8x, B727, B737 aircraft, especially when flying in visual, daylight conditions. It may be a realistic strategy in the case of B747, B757 and B767 aircraft. The total removal of electricity is not an option on Fly By Wire (i.e. computer controlled) aircraft such as Airbus A320, A330, A340 and Boeing B777.
NOTE: Pilots are invited to contact the author with a list of operational constraints pertaining to their particular aircraft when adopting the strategy of removing all electrical power as a means to fight an inflight electrical fire. (See contact details below)
As mentioned earlier, the current generation of jet aircraft such as the Boeing B777, Airbus and MD11 cannot be effectively flown without electricity, unlike earlier generation jets such as the DC9. If a person had an electrical fire in their house, the first thing that person would do is remove the electrical power to the house by pulling the main house fuse, but that option is not available with aircraft like the B777 and Airbus. The aircraft industry as a whole - that is aircraft manufacturers, government regulators, airlines and pilots - have failed to adequately address the problem of inflight electrical fire and are simply burying their collective heads in the sand about the issue. The concept of a 'Virgin Electrical Bus' is an elegant solution to this complex problem. It is the author's opinion that not only should it be a mandatory item in all future aircraft designs, a minimal version of the same should be retrofitted to all transport aircraft currently flying.
Alex Paterson (December 2000)
1. Swissair Flt 111 experienced a smoke-in-the-cockpit emergency shortly after reaching top of climb out of New York on the night of 2nd September 1998. The aircrew commenced a diversion to Halifax, but within 20 minutes of the first sign of electrical smoke the aircraft crashed into the sea off the Nova Scotia coast whilst the crew were still attempting to carry out the lengthy trouble-shooting checklist. The electrical fire is thought to have been associated with the un-approved installation of an in-flight entertainment system (which incidentally had no ON/OFF switch installed). There is some evidence that Kapton wire in the aircraft may have caused or contributed to this crash. It would appear the lengthy trouble-shooting checklist also contributed to the disaster because electrical power was not removed from the electrical circuits involved. MD11 aircraft cannot be effectively flown without electricity, so the removal of all electricity from the aircraft was not a viable option available to the SR111 aircrew. For more information about this incident see:
NOTE: It is the opinion of many aviation safety experts (including the author) that the SR111 crash will prove to be a watershed event because it will lead to far reaching changes within the industry with regard to the design of aircraft electrical systems and wire, as well as numerous other aspects of aviation safety.
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2. For more on Kapton wire see:
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3. IASA Aircraft Wire Related Incident Database
There is growing evidence that the incidence of aircraft wire related 'events' have been under reported by the US Federal Aviation Authority (FAA) for decades, usually associated with the mis-recording or non-recording of incidents in the relevant FAA and aviation industry databases. Whether this is part of a deliberate process to disguise the extent of aircraft wire incidents from public scrutiny has yet to be determined. What is clear is that both the FAA and aircraft manufacturers are in no great hurry to remedy the situation. For more on this issue see:
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4. With no electricity, flight control of the:
Neither of these configurations provides pilots with enough control to effect a safe approach and landing, especially if there is a crosswind blowing. (which as just about always)
Juxtapose this unsatisfactory arrangement with the 40 year old DC9 which has lost all hydraulics and all electricity - the aircraft remains, in both feel and performance, virtually the same aircraft to operate as a fully functional DC9.
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5. Arc-Fault Circuit Interrupter (AFCI) circuit breakers. There are significant design constraints facing the concept of AFCI circuit breakers for aircraft, not in the least being the likelihood of high frequency attenuation associated with the long lengths of wire in aircraft and the problems associated with using the aircraft airframe as the electrical current return path. Because of these design problems, most aviation electrical experts don't expect to see reliable AFCI circuit breakers in aircraft prior to 2005, if at all.
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6. Ground-Fault Circuit
Interrupter (GFCI) circuit breakers. GFCI are acknowledged by
most electrical experts to be the best way to protect electrical
wires, as well as provide some form of protection to electronic and
electrical components themselves, something the current generation of
bi-metallic thermal trip circuit breaker cannot provide. However,
GFCI require the existence of individual neutral return wires,
something which are not installed in the current generation of jet
transport aircraft due to the extra weight of such wires. The current
generation of jet transport aircraft use the airframe as the return
path of electrical current to save weight.
NOTE: The installation of separate neutral return wires would add
about 1000kg to the weight of a B747, however see note
2 below)
It is worth noting that the use of a metal structure such as an airframe as a current return path is not permitted by electrical safety codes in any other situation except aircraft. Allowing electrical currents to flow in the ground plane of a metal structure; be it a ship, a mobile home, an office building, a home or an aircraft; results in a number of potentially dangerous circumstances which include:
NOTE 1: In researching information about GFCI circuit breakers, I was sent the following assessment of aircraft electrical design by a non-aviation electrical expert concerning the current practice of using the aircraft airframe as an electrical current return path. He was horrified by the concept and said:
"If this business of eliminating a Neutral wire to save weight and costs were valid, and the concept were really sound, then consider this illustration of an office example using the same wiring system. Configure a distributed computer system of several PCs, interconnected by data cables. Make the 'system' do something in which people's lives are dependent upon total system reliability. Put the PCs on an aluminium table without insulation of any kind. In order to save weight, connect the external power cable return (neutral) wire directly to the table top. Connect the return wire from each PC to the table top by the shortest path. Remove all PC insulating devices and set the PC motherboard directly on the tabletop for "proper" operation. Now run a single "hot" wire from the external power cable and connect to each PC. Place a narrow, cramped semi-reclining aluminium chair on the table top and be seated. Have an associate plug in the external power cable and start the computers. You now have the electrical equivalent of a seated passenger at the boarding gate, waiting to fly. Does this sound like a good idea?"
NOTE 2: The extra weight associated with installing neutral return wires in aircraft is offset by numerous advantages which include:
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7. FAR 25 pertaining to Electrical System redundancy states in part:
COMMENT: Aircraft wires associated with a plethora of diverse
systems and whose power source and voltage are often different are
currently all bundled together in massive wire looms. (often
involving hundreds wires) An explosive arc-tracking event
invariably severely damages surrounding wires taking out unrelated
systems and causing further electrical fires and explosions. TWA
Flight 800 which exploded over New York on 17 July 1996 is thought
to have been caused by low voltage fuel tank quantity wires
shorting out onto adjacent high voltage wires triggering an
explosion in the centre fuel tank and destroying the aircraft.
COMMENT: As above, this requirement cannot be met due to the fact
that the wires from various systems (including emergency power
items) are usually bundled together in massive wire looms.
COMMENT: As above, this requirement cannot be met due to the fact
that the wires from various systems (including emergency power
items) are usually bundled together in massive wire looms.
COMMENT: The current generation of bi-metallic circuit breaker
used in aircraft have some serious flaws rendering them inadequate
for the task of being aircraft "circuit protective devices" as
stipulated in FAR 25.1357. Bi-metallic circuit breakers
cannot detect the micro discharges of electrical current
through hairline cracks in the insulation material of aircraft
wire. (a condition known as 'ticking') Ticking faults can
eventually lead to a major 'flashover' event in which the
insulation material of the wire catastrophically fails leading to
a very high current discharge of energy through the wire to the
surrounding aircraft structure. (i.e. a short circuit) In the case
of KAPTON wire, this flashover event is usually explosive,
resulting in severe damage to the surrounding wires and aircraft
structure with potentially catastrophic results. (e.g. Swissair
SR111 crash) The situation can be further exacerbated by the fact
that bi-metallic circuit breakers can actually 'weld' themselves
closed due to the very high heat generated in the circuit
breaker during a flash-over event. Arc-Fault Circuit Interrupter
(AFCI) and Ground-Fault Circuit Interrupter (GFCI) circuit
breakers may be the answer to these problems, however see
footnote
3 and footnote
4 above.Source: FAR 25 - Electrical Systems and Equipment: http://www.faa.gov/avr/AFS/FARS/far-25.txt
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SMOKE/FUMES/FIRE ELEC
Condition: A concentration of electrical smoke/fumes or fire is identified.OXYGEN MASKS AND SMOKE GOGGLES ON
(If required)CREW COMMUNICATIONS ESTABLISH
(If required)If smoke/fumes or fire source can be determined:
ELECTRICAL POWER (affected equipment) REMOVEIf smoke/fumes or fire is persistent:
Plan to land at the nearest suitable airport.
Source: Boeing B777 Flight Manual
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Copyright © Alex Paterson (2000)
MASTER
INDEX of articles written, posted
online or recommended by Alex Paterson
Alex PATERSON is an Australian airline pilot by profession. He writes articles and advises on issues pertaining to aviation, politics, sociology, the environment, sustainable farming, history, computers, natural health therapies, esoteric teachings and spirituality.
He can be contacted at:
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The document, 'Aircraft Electrical Fire - the case for a Virgin Electrical Bus' is the copyright © of the author, Alex Paterson. All rights reserved by the author. Notwithstanding this, the document may be reproduced and disseminated without the express permission of the author so long as reference to the author is made, no alterations are made to the document and no money is charged for it.
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