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Safety in Avionics: Needless Nakedness in the Face of Fire

By David Evans | June 1, 2000
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If a pilot’s greatest fear is that of in-flight fire, U.S. airline pilots are facing this frightening specter an average of three times a day. The realization of fire on board always sends a jolt to the heart. In one out of every three of these cases, crews were sufficiently concerned to execute a precautionary landing.

The threat posed by "this ravenous and noxious enemy" was described vividly in a recent article for Canadian bush pilots (see sidebar below).

The finding that airline pilots are reporting three events daily comes from recent research by Jim Shaw, an airline pilot and manager of the in-flight fire project undertaken recently by the Air Line Pilots Association. Consider his research the first "work product" of this important initiative.

Shaw tapped the Service Difficulty Report (SDR) database, trolling for reports covering the first 10 months of 1999 with keywords like "smoke and not false warning" and "insulation or wiring, char, burn or short." What he found should send up the proverbial storm flag:

• High numbers–964 smoke or fire events on transport aircraft in the U.S. and Canada.

• High temperatures–578 were high-temperature events. These were subjectively defined as incidents involving any reference to smoke from a solid material or popped circuit breakers. These events vastly outnumbered about 400 reports of air contamination (possibly combustible).

• Mostly electrical–A detailed look at 392 high temperature events showed that 80% involved electrical systems and components (see photographs on page 58).

• Mostly unprotected–About 380, or 66%, of the 578 high-temperature events occurred in or near the cabin, galleys, lavatories and cockpit (including 50 high-temperature events in the electronics and equipment, or E&E, bay located immediately below the cockpit). To be sure, these are the areas where electrical systems are concentrated, so the failure density correlates with equipment density. Significantly, these also are the locales, excepting the lavatories, where neither built-in detection nor fire suppression is provided.

• Mostly inaccessible–In the overwhelming number of cases, crews had limited ability to recognize, gain access to, or control the malfunction. Aiming for the nearest airstrip and hoping for the best was often the option of first resort. "If the crew didn’t know where the smoke was coming from, they didn’t have access or controllability," Shaw observed. "Control of the event, even at a minimal level, was possible by the crew in less than 40% of events, and access was possible in less than 20%."

• Making it worse–Resetting tripped circuit breakers generally made things worse. In eight of 12 events where popped breakers were reset, additional smoke, arcing or damage occurred. In the other four cases, a serious malfunction had occurred and resetting the breakers injected the distinct possibility of further damage.

• Many precautionary landings–These 900-odd events triggered more than 350 unscheduled landings. In many cases, evidence of electrical arcing was discovered. After routine repairs, the aircraft were returned to service. Even if these events were trivial, which many were not, Shaw believes that safety was compromised. "Every day there’s at least one crew landing at an airport they are not familiar with," he observed.

• Events are undercounted–Based on the mention of "several air returns with smoke odor" in one report where the crew made a precautionary landing, Shaw believes the SDR database, even though it is the richest source of such data, may significantly undercount actual events. "These are minimum numbers," Shaw maintained.

• Regulators may be clueless–Unless Federal Aviation Administration (FAA) authorities are assiduously mining the SDR database, they may be clueless as to the frequency of this activity. Of 155 SDR-reported events that necessitated an aborted takeoff, return to the block, emergency descent or unscheduled landing, only 21 such cases were found in the FAA incident database for the same time period.

Even if they were cut in half, Shaw’s numbers are staggering. To be sure, he was examining a period following the September 1998 crash of a Swissair MD-11, in which an out-of-control electrical fire is the primary suspect. In the wake of that disaster, sensitized pilots, sniffing the slightest whiff of smoke or the distinctive odor of an electrical malfunction, may have been landing with unusual alacrity.

Nevertheless, what may be required is a complete rethinking of the measures needed to cope with in-flight smoke and fire. On this score, there are plenty of ideas:

• Smarter placement–Simply placing smoke/fire detectors in each of the main air-conditioning ducts would greatly assist pilots in isolating the source of smoke, enabling them to better differentiate between "aerosolized" oil leaking into the air-conditioning system and the potentially greater hazard posed by an electrical fire.

• More coverage–"We can’t keep living in the Stone Age. We need detection and suppression throughout the aircraft," Shaw urged. Priority should be placed on inaccessible areas of the fuselage. It should be noted that every square inch of a typical nursing home is covered by detection and suppression. Nursing homes are cited here because many of the elderly have limited mobility, as do passengers confined in the "aluminum tube" of an airliner.

• Better detectors–The smoke detectors in aircraft cargo compartments have a false alarm rate of about 100-to-1. The epidemic of false alarms undermines pilot confidence in the smoke-detection equipment and certainly complicates their decision-making. Researchers believe that new detectors, under development for low-income housing, could reduce the false alarm rate tenfold. If they’re cheap enough for public housing, these new detectors should be cheap enough for public air transport.

• Better suppression–In early May, the U.S. Navy tested a water-mist fire suppression system in the cabin of a retired Boeing 737. As of this writing, the results are not known. However, in earlier trials on the USS Shadwell, a retired amphibious warship outfitted as a test vessel, dramatic results were achieved. A 20-gallon (76-liter) supply of water in mist form doused a raging fire in a 60,000-cubic-foot (1,700-m3) machinery space within seconds. The potable water supply on an airliner can be tapped for use in a water mist system, with just 6 to 10 gallons (22.7 to 37.8 liters) deemed more than sufficient. As for the effect of water mist on sensitive electronics, the Navy found that a 30-minute exposure to the mist had virtually no effect on electrical and electronic components.

• Better access–Many electrical short circuits and fires propagate behind panels. Access ports could be fitted so that crews could better use their hand-held extinguishers to squirt fire suppressant into these spaces, without having to expend precious time with screwdrivers or fire axes opening the panels.

• Better procedures–Instances of in-flight fire and smoke need to be treated as equal to the loss of an engine on a twinjet. Procedures should emphasize getting the aircraft pointed in the right direction immediately for landing. Emergency checklists should be designed to relieve the crew of troubleshooting, focusing on diverting the flight, and depowering all but flight-essential electrical systems. As an example, for Delta Airlines’ new B767-400, the first three items on the smoke/fire emergency checklist consist of: (1) don masks and smoke goggles, (2) establish communications, (3) begin the divert.

With respect to helping crews to quickly identify flight-essential from other systems, Bill Sell, an engineer with German circuit breaker manufactuer E-T-A Elektrotechnische Apparate GmbH, suggests a standardized color-coding system. The breakers for critical circuits could be colored red. "If it pops, you know immediately a flight essential circuit is affected," he said.

"You could put a colored cap over the button, or color-code the rating label," Sell explained. The color-coding, he believes, would be a boon to pilots who are "under pressure anyway" when the breakers start popping. One might say that his simple scheme would help pilots to "sweat the red stuff."

Those 900+ reports Shaw found present a stark picture: pilots are pretty naked in the face of a possible in-flight fire. They, and their trusting passengers, deserve better.

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