Swissair Probe Focuses on Insulation
By Don Phillips
The thermal insulation blankets, which look similar to home insulation, met all Federal Aviation Administration standards for fire retardance and were used in aircraft for many years. But a series of aircraft fires between 1993 and 1995 persuaded McDonnell Douglas Corp., manufacturer of the Swissair MD-11, to recommend in 1997 that the blankets be replaced at "the earliest practical maintenance period" on at least 1,000 jets.
Investigators for the Transportation Safety Board of Canada are far from determining the cause of the Sept. 2 crash of the New York-Geneva flight off the Nova Scotia coast, in which 229 people perished, and the role of the insulation blankets -- if any -- will not be determined for some time. However, accident investigations often highlight safety issues that may have little to do with the crash.
After the crash, Boeing Co., which merged with McDonnell Douglas last year, decided to bring all carriers that use McDonnell jets together at a meeting, beginning today, to consider speeding up implementation of previous manufacturer recommendations regarding fire and smoke. Sources said the blankets -- made of a metalized Mylar -- will be one of the major issues under discussion at the session, in Long Beach, Calif.
The blankets insulate the aircraft from heat and noise. They are installed under the aircraft skin and in other areas where heat might be a problem, such as the electronics bay at the front of the aircraft.
They were placed on at least 1,000 McDonnell Douglas aircraft before their use was stopped. A spokesman for Boeing said the company does not know how many of those planes have been retrofitted with newer insulation. The insulation apparently was not used on planes produced by the two major passenger jet manufacturers, Boeing and Airbus Industrie.
Information developed so far in the Swissair investigation indicates that heat, and possibly flames, spread through portions of the cockpit and the forward portion of the plane. "Heat-distressed" wreckage from the cockpit has been found. And now, according to investigative sources, a piece of the forward cabin interior above the left front door has been found with heat distress.
Jim Harris, a spokesman for the Transportation Safety Board of Canada, confirmed that a small amount of both types of insulation had been found, none of which exhibits indications of burning. Large amounts of wreckage will likely be recovered next week when a major dredging operation begins, he said.
The insulation blankets are unrelated to the issue of wiring insulation, including Kapton insulation, which received much attention after the crash. Sources close to the investigation said there is no indication so far that Kapton was a factor in the crash.
The pilots reported smoke in the cockpit and then for about 10 minutes made an orderly descent to 10,000 feet to dump fuel. Although they had donned oxygen masks and prepared the cabin for an emergency landing, they did not display a sense of urgency about their situation until they declared an emergency and told controllers "we have to land immediate."
Within less than a minute, the aircraft's electronic systems apparently shut down. Little is known about the last six minutes before impact because the two on-board recorders and the plane's radar transponder had stopped.
Sources said that the plane's cockpit voice recorder offers little help in determining what the pilots saw that persuaded them to declare an emergency, but that it is clear the situation suddenly deteriorated in some way.
As a part of the probe, investigators have learned of at least three aircraft fires between 1993 and 1995 in which electrical short circuits had set fire to insulation blankets that became fuel for damaging fires -- even though the blankets met FAA standards.
In none of those cases did the blankets start the fire. But the blankets allowed it to spread rapidly in the three incidents, which all happened on the ground, allowing passengers and crew to escape. In a fourth instance, maintenance crews started the fire when hot metal chips from an air drill ignited a blanket.
The first incident, on Nov. 24, 1993, involved a Danish twin-jet MD-87 at Copenhagen. According to the Aircraft Accident Investigation Board of Denmark, the plane was taxiing to the gate when smoke started to emerge from the service units at the rear of the passenger cabin. After passengers disembarked, the smoke intensified "drastically."
"A fierce fire then erupted and spread very quickly," said an FAA report based on the Danish investigation. "Investigators determined that the thermal acoustical insulation blankets acted as fuel sources which helped to spread the fire."
One of the fires involved an MD-11. On Sept. 6, 1994, the crew of a China Eastern MD-11 noticed smoke in the cockpit as pilots prepared to start their engines at Beijing. They discovered a roaring fire spreading through the electronics bay beneath the cockpit that caused heavy damage.
The Civil Aviation Administration of China, in a May 24, 1996, report, said that molten metal from a short circuit dropped on insulation blankets, igniting them. The CAAC recommended a "prompt and positive response" from the manufacturer and the FAA and said the method of testing and certifying insulation material should be changed.
In a July 24, 1996, reply, the FAA promised to look into the matter but said the agency had already addressed the core cause of the fires -- wire chafing. The FAA did not directly address changes in tests, instead noting that the burn tests performed by the CAAC are not required by the FAA. "While the tests you conducted are illustrative, they do not invalidate the certification of the material," the FAA letter said.
The manufacturer's service bulletin called for replacing the insulation at the "earliest practical maintenance period," which generally would mean heavy maintenance when the aircraft is stripped down to its frame. The last heavy maintenance on the Swissair plane was in August 1997, two months before the service bulletin was issued but 10 months after McDonnell Douglas circulated a letter saying it probably would take that action.
A Swissair spokesman in Zurich, Hans Klaus, said that parts of the insulation would likely have been replaced during "C checks," less-heavy maintenance when parts of the aircraft skin might be removed. He said, however, that he could not immediately say what parts of the airplane had been changed out.
"This was a non-priority recommendation from Boeing, but it never gained a recommendation from the FAA," Klaus said.
FAA spokesman Elliot Brenner said yesterday that the FAA does not comment on ongoing investigations.
But the Boeing all-operators meeting in Long Beach is likely to recommend stepped-up action on the insulation blankets and other items. Metalized Mylar was used in the older insulation because the metal covering provides a better water barrier and prevents the blanket from gathering moisture. The recommended replacements are non-metalized Mylar or Tevlar.
Among the other items, some of which date back to 1960, are replacement of wire bundle clamps, circuit breakers and wire assembly supports. The meeting will even revisit the issue of the lavatory flush-pump motor's circuit breakers, which caused an Air Canada in-flight fire in 1983.
Ron Hinderberger, Boeing's director of aviation safety investigations, said the two-day meeting is a normal reaction to any crash. He said Boeing and the airlines will review the service bulletins and will discuss with the airlines how they have handled the manufacturer recommendations.
"We expect more expedited action on some types of service bulletins," he said.
Among the airlines signed up to attend the meeting are Federal Express, Japan Air Lines, Swissair, Martinair, KLM, China Eastern, Alitalia, United Parcel Service, Delta, Reno Air and Northwest. Other airlines may also attend.
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