Safety News: The War is Still On

By Jim McKenna, Managing Editor

In aviation, we pride ourselves on safety. It is not just the engineer, mechanic, pilot, or inspector who is responsible for safety, we assert to basically anyone who asks. Each is and each backs up all the others. This robust system is what makes flying safe.

But pride can degenerate into delusion. This is illustrated by investigations into the 1998 crash of a Swissair MD-11 and last May's breakup of a China Airlines Boeing 747.

The Transportation Safety Board of Canada in late March wrapped up its investigation of the September 2, 1998 Swissair crash. Flight 111's pilots detected smoke in the cockpit 53 minutes into the New York-Geneva flight and diverted to Halifax, Nova Scotia. But the trijet nosed into the Atlantic, killing all 229 on board.

The TSB's detective work is fascinating, and its report (available at http://www.bst.gc.ca) well worth reading. It contains two salient findings. First, regardless of what the pilots had done or how fast they acted, the fire would have overpowered them before they reached Halifax. Second, the fire started by arcing in the cockpit's right rear overhead was lethal because it was fed by elements that shouldn't exist in combination on an aircraft"”elements that were all known (or should have been) before the accident to those who pride themselves on protecting safety.

The chief arcing suspect was wiring for the MD-11's in-flight entertainment network (IFEN). Its designer and the FAA signed off on an installation that hooked the IFEN to a primary bus, which left the pilots unable to turn it off and stop the arcing.

That arcing ignited lining on thermal/acoustic insulation that everyone assumed was not flammable because it had passed FAA certification. Chinese investigators had told the FAA and Boeing months before the Swissair accident of an MD-11 that proved the insulation was flammable, but nothing was done until after Flight 111 crashed. Insulation blanket certification standards have since been revamped, the TSB noted, but other material that is just as flammable contributed to the Swissair fire and is still flying.

Finally, the TSB noted, circuit breakers on Flight 111 failed to cut off power to the arcing circuit. Breakers fail in one of two ways, the Canadian investigators noted. They trip too easily, which is a nuisance but not necessarily a safety problem, or they fail to trip, which leaves the circuit unprotected and creates a safety problem. Is that news to anyone?

When China Airlines Flight 611 broke up at 35,000 feet over the Taiwan Straits, all 225 on board died. Investigators for the Aviation Safety Council of Taiwan are still searching for the causes of that crash. But their findings to date prompted the U.S. National Transportation Safety Board to call for a review of all repairs that may hide damage to the pressure vessels of transport aircraft.

It seems that about seven months after the accident aircraft was delivered new to China Airlines in July 1979, the 747 suffered a tail strike that seriously gouged its aft belly skin. The airline's engineers came up with a temporary repair installing doubler plates on the belly. China Airlines said a permanent repair was later done, but investigators have found no proof of that. Furthermore, the temporary fix apparently was done incorrectly.

Boeing calls for removal of the damaged skin before a doubler is installed, according to the NTSB, but China Airlines mechanics placed the doublers over the damaged skin. Over more than 22 years, the tail-strike gouges concentrated stresses that caused many small cracks along a rivet line"”10 feet worth of cracks. Such cracking, which metallurgists call multiple site damage, is like perforation in paper. It creates the potential for a piece of metal to unzip from its frame, especially when the metal is part of the airplane that is repeatedly exposed to pressurization cycles. This is what happened to the upper fuselage of the Aloha Airlines 737 in 1988, and now apparently is a suspect in the search for why that China Airlines 747 burst open at altitude.

Incidents like these belie the robustness of safety. Where were all the engineers, mechanics, and regulators who saw that the Swissair MD-11's IFEN was hooked to a primary bus, or that failed breakers need a better fix than a reset/replacement? Why do we tolerate unnecessary fire hazards in areas unprotected by detectors or extinguishers? Who was it that failed to challenge the continued use of a temporary repair that was deficient to begin with? Perhaps pride has no place in an endeavour that demands constant, untiring vigilance.

As U.S. troops marched into Baghdad in early April, a radio reporter asked a Marine colonel how he felt about the achievement. The colonel's answer held a lesson for everyone in aviation. He pointed out that the war was still on. Then he said: "As soon as you think you're safe, that's when you're going to start making mistakes. And those mistakes are going to get Marines killed." They'll get passengers and crews killed, too.

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