Editor's Note

Safety: From Diversion to Desperation

By David Evans | May 1, 2003
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Already in a dire situation, with one system after another failing, Capt. Urs Zimmermann must have looked up with a startled expression when the ceiling panel over his seat in the cockpit of the Swissair MD-11 burned through. The opening unleashed a torrent of hot gas and a dark cloud of charred fiberglass particles, released by the insulation blankets whose flammable covering had burned away.

At that moment, Zimmermann and First Officer Stefan Loew called, "Mayday, Mayday, Mayday" on the radio. The urgency of their divert to Halifax now was a matter of utter desperation, the planned overnight flight from New York to Geneva at this point completely forgotten.

Zimmermann and Loew were in a dark cockpit, gasping futilely for breath when the line supplying emergency oxygen to them was melted by the heat of the inferno raging in the so-called "attic" space above the cockpit. End caps on the air conditioning ductwork had burned away, fanning the fire overhead with a bellows-like effect. When the aluminum end cap on the steel oxygen line burned away, the effect of pure oxygen on the fire was nearly explosive in its intensity.

As the fire burned through bundles of electrical wiring and power cables, vital systems began failing–the electronic version of biological death, when the body’s organs begin a fatal sequence of shutting down. In the cockpit of the stricken MD-11, large red "Xs" appeared on five of the six glass cockpit displays, showing that they were no longer functional. Maybe the one remaining display directly in front of Zimmermann showed partial information for a moment, but a red X probably replaced its flickering information, too.

The pilots were left with a rudimentary compass, pulled into position in front of the windscreen, and a standby instrument located near the center bottom of the instrument panel. It, too, failed when the fire raging above severed its electric power supply. With the master caution alarm sounding insistently, Halifax’s Runway 06 was just 30 miles distant. So close, yet so far. Zimmermann and Loew didn’t make it. The airplane hit the water nose-down, in a steep bank, at a speed of some 300 knots. The force of deceleration–impact really–was calculated at some 350 Gs, killing all 229 aboard instantly. Broken bodies and broken aluminum were "commingled," in the delicate euphemism employed by Canadian investigators.

A life jacket was found on the remains of one passenger, a pilot. Even though smoke from the fire raging overhead never clouded the cabin, he must have known the situation was more serious than the flight attendants’ calming reassurances suggested.

Capt. Zimmermann was not in his seat at the moment of impact. Most likely the rain of melted plastic and the searing downrush of hot gas had driven him out when the curved ceiling panel gave way. The effect was perhaps like that of a match held too close to a strip of celluloid motion picture film. It is a common image–the film darkens, then a hole breaks open and the burnt edges of the film melt away. In short order, the film is consumed entirely.

Investigators with the Transportation Safety Board (TSB) of Canada recently concluded their exhaustive postmortem of the 1998 crash, declaring in a March 27 press conference that the deadly fire was a "wake-up call" to an industry that has "not moved decisively" to reduce the hazard posed by flammable materials in jetliners. In a jumble of wires recovered from the wreckage they found evidence of a tiny electrical arc on a cable supplying power to the airplane’s in-flight entertainment network. The solidified evidence of once molten conductor was so tiny, its significance was only evident under 22x magnification. It was the match that started the conflagration. The arcing energy, not enough to trip the circuit breaker, had been sufficient to ignite flammable metalized mylar thermal acoustic insulation blankets. The fire spread, feeding on other flammable materials, some supposedly fire-resistant but readily igniting nonetheless with the rapacious speed of a grassfire on the African savanna.

The first telltale sign misled Zimmermann and Loew. They thought the odor and the wisp of smoke from the air vent overhead was indicating a problem with the air conditioning system. The two pilots had no way of knowing that the tiny spark had set off a train of arcing events and ignited a hidden fire above and just behind them. The smoke flowed down to the electronics and equipment (E&E) bay, eventually following a corkscrew path forward toward the vents near the pilots’ seats. The unseen smoke above also drifted back into the attic area over the cabin. The smoke was deceptive, showing itself, then disappearing, then showing itself again as the fire gained strength.

Still thinking the problem was a malfunctioning air conditioning system, Zimmermann elected to cut the flight short and land the airplane. He told the cabin crew to be prepared to land at Halifax in 20 to 30 minutes. His tone, captured on the cockpit voice recorder, was one of concern, not the edginess of a captain fearing a dire emergency.

When, as part of the troubleshooting checklist for smoke and fire of unknown origin, the ventilation fans for the cabin were turned off, the smoke reversed course. Now, instead of being sucked aft, it flowed toward the cockpit.

It was too late to save the situation. A good two minutes before the pilots conceivably could have brought the stricken jet over the runway threshold, systems were falling off line and the cockpit environment was turning deadly. Even if they had made it that far, without leading edge slats, autospoilers, antiskid brakes and other systems, investigators believe Zimmerman and Loew would not have been able to stop the airplane on a runway surface. They would have needed at least 9,600 feet (2,926 meters) to come to a stop. Halifax’s runway 06 is 8,800 feet (2,682 meters) long.

What would have helped? Earlier detection. Fire detection and suppression in the attic space, not required but part of the investigators’ battery of corrective recommendations, would have enabled the pilots to determine earlier if they were facing an air conditioning problem or an electrical system malfunction.

If the airplane had not been built with flammable materials, the arcing event would not have had the effect of a match on dry tinder. TSB officials were blunt on this point: the use of any material in an airplane that can be ignited, or that sustains or propagates a fire "constitutes an unacceptable risk." The insulation material had been certified for use based on a simple Bunsen burner test, not the much higher heat of electrical arcing.

Remove the flammable materials, and a tiny spark needn’t be a death sentence. It will take years to do that, maybe a decade. To retrofit fire detection and suppression in the attic space and to institutionalize improved firefighting training for flight crews, also called for by the TSB, will take years.

Modest improvements, however, can be made in the short term. In 1999 Capt. Ken Adams propounded a new approach to cockpit and cabin fire safety. Now retired, Adams was an MD-11 pilot with Delta Air Lines at the time of the Swissair accident. He cited an in-flight fire aboard a Federal Express (FedEx) DC-10 in 1996, as the aircraft was cruising at 33,000 feet, the same altitude as the Swissair MD-11.

The FedEx crew landed the airplane in 20 minutes and evacuated before the DC-10 was consumed by fire. Early detection prompted the FedEx captains’ decision to land immediately.

Adams suggested placing smoke detectors in each of the ducts supplying air to the cabin and cockpit. Better yet, evenly space smoke detectors close to electrical wire and bundle routings.

Adams also suggested that apertures could be placed on the wall and ceiling panels in the cabin and cockpit at areas with a high concentration of electrical wiring and flammable material behind them. Thus aircrews could more effectively employ their handheld fire extinguishers to quickly apply agent into these concealed spaces.

Against the day of the strategic fire improvements called for by the Canadian investigators, duct detectors and access apertures could make all the difference between a prudent diversion and a desperate race against imminent death.

(The full report of the TSB investigation can be viewed at www.tsb.gc.ca/en/reports/air/1998/a98f0003/ eReport/SR111_200303.pdf.)

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