To improve safety, it makes sense to address problems like on-board fire that cause most deaths and for which there are ready solutions

Considering how often minor electrical fires happen on commercial transport aircraft without harming anyone on board, last week’s US National Transportation Safety Board (NTSB) recommendations following several such incidents in Bombardier CRJ200s might seem a little over the top. The recommendations are certainly strongly worded – almost panicky in their determination to convince the Federal Aviation Administration to take action.
But although in this case the NTSB is addressing a serious risk, it is a highly specific, fully identified technical fault, not a generic problem – for example, electrically generated aircraft fires. Identified technical faults are – relatively – easy to deal with.
Meanwhile, it is definitely not “over the top” to worry about fire of all kinds in an airframe. That issue should be much higher up the industry safety priorities list than it is now. Despite the fact that there is an average of one diversion a day because of smoke in the cockpit or cabin in the USA alone, modern aircraft only have effective fire detection and suppression systems (FDSS) in the engines and auxiliary power unit. An exception is the latest generation long-haul aircraft and those operating under extended twin engine operations (ETOPS) rules which have active freight bay FDSS.
In the cockpit and cabin, the FDSS consists of people’s noses and eyes, and a few hand-held fire extinguishers available to a crew with only a modicum of training in how to use them to best effect. The fact that smoke may emerge from the edge of a particular internal fuselage cladding panel is not necessarily an accurate indicator of where the heat source is, so what are the crew to do to direct the extinguishant effectively? And since short-circuiting does not necessarily trip circuit breakers (CB) until a fire is already established, what are the pilots to do to identify the source of the problem?
The statistic about the frequency of on-board smoke-caused diversions in the USA is just one of a collection of alarming revelations in an analysis of in-flight fire risk by Capt John Cox, head of Washington DC-based Safety Operating Systems. His report quotes an International Air Transport Association (IATA) study of the problem that reveals about 1,000 in-flight smoke events occur annually – mostly in the cruise – and that information comes from a big sample of airlines, but not the whole world fleet. A review of the period 1987 to 2004 shows that the four leading causal categories of fatalities – out of 17 – in commercial jet air transport were loss of control, controlled flight into terrain, specific component failure (non-powerplant) and in-flight fire. Taking these categories one by one, Cox argues that loss of control still occurs even on flight-envelope protected aircraft, and it has multiple causes – often human factors-centred – so it is a complex problem to solve: controlled flight into terrain can be countered by terrain awareness and warning systems; in the case of specific component failure the solutions required depend on which component it was; finally, in the case of on-board fire, there are many potential solutions that are not applied to best effect or not applied at all, Cox argues. So this, he says, is the safety issue on which industry resources could be deployed with the best potential reward in terms of saved lives. Out of the 226 fatal accidents in the period, 10 were caused by in-flight fires, says Cox.
Cox is right in his arguments. The Swissair 111 crash off Nova Scotia in 1998 was the most dramatic wake-up call the industry could possibly have been given regarding onboard fire, especially electrically generated fire.
This particular fire started with a short-circuit in the electrical supply to the in-flight entertainment (IFE) system and propagated via contaminated thermal/acoustic insulation and other materials. By the time the aircraft crashed the pilots would have been blinded by smoke and poisoned by fumes they could do nothing to dissipate. The solution is not to eliminate IFE systems as this could have occurred in any electrical wiring bundle. In this case it was worse because, on installation, the IFE system supply was not taken from the cabin power busbar, so when the crew isolated the cabin the circuit was still live.
New electrical equipment is added to aircraft frequently, so disturbance to wiring bundles and the potential for mistakes in routeing are just some of the issues. On-board fire is now the lowest hanging fruit on the safety tree. The industry should reach for it.

Source: Flight International