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 flown without electricity, unlike earlier generation jets such as the DC9.
The Virgin Bus
Inflight electrical fire would be best handled by the provision of a separate standby electrical wiring system which was powered by a totally separate Battery and Air Driven Generator (ADG). It would be used in the event of an in-flight electrical fire to power essential aircraft systems normally available under Standby Electrical power. (i.e. items normally located on the Standby Electrical Bus, Hot Battery Bus and Battery Bus)
In normal operation, the Virgin Electrical
wiring system would remain disconnected and unpowered except
for preflight checks.
See detail at www.iasa.com.au/virginbuss.htm
Clearly the Virgin Bus proposal needs much design work to take into account numerous engineering considerations such as:
Other significant design initiatives to reduce the risk of inflight electrical fire include:
NOTES 1: At present no jet transport aircraft currently in production complies with the US Federal Aviation Regulation (FAR 25) pertaining to electrical system redundancy in the event of an electrical fire or arc tracking event. 4
2: At present no jet transport has an effective strategy in place to deal with an inflight electrical fire as evidenced by the current Boeing B777 electrical fire drill which simply instructs aircrew to "Remove Power" from the affected circuit without providing them with any instructions as to how they should actually identify or determine the affected circuit(s) before removing power from them. Leaving power on the normal system wiring is to invite cascading systems malfunctions as wiring bundles flash-over. As a minimum requirement an aircraft electrical fire/smoke of unknown origin drill should instruct aircrew to immediately "power down" to Standby Electrical Power in order to protect the aircraft electrical system integrity. This action will markedly reduce the likelihood of trouble-shooting (and isolating) the fault and may in fact continue to power the faulty wiring, component or equipment. So what is actually required is a redundant fall-back system that can be selected at the first sign of trouble. This will avoid the irretrievable loss of vital systems and avoid any outbreak of a fire in hidden areas being stoked by power remaining on the wire. Because presently recommended pilot action is to land ASAP in the event of smoke, the provision of a fallback system may remove the urgency from the situation and minimize the possibility of an accident being generated by undue haste, particularly in bad weather/at night. 5
As mentioned earlier, the current generation of jet aircraft such as the Boeing B777, Airbus and MD11 cannot be flown without electrics, 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 supply to the house by pulling the fuses, but this 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. This is particularly apparent in the SFAR (Special Federal Airworthiness Reg) that addresses the considerations for ETOPS (extended range operations over oceanic and desolate unlandable areas. The concept of a Virgin Electrical Bus is a significant step towards providing a solution to this complex problem and affording a level of redundancy that presently does not exist.
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 20 minutes later 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 unapproved 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 flown without electricity, so the removal of all electricity from the aircraft was not an 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 should 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.
3. 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. Because of these design problems, most aviation electrical experts don't expect to see reliable AFCI circuit breakers in aircraft prior to 2005. However some airlines are trialing them at present (Feb 04) in non-vital areas.
4.FAR 25 states in part:
Source: FAR 25 - Electrical Systems and Equipment: http://www.faa.gov/avr/AFS/FARS/far-25.txt
5 B777 ELECTRICAL FIRE DRILL
Source: Boeing B777 Flight Manual
Copyright © Alex Paterson (2000)