It is the closest thing now to finding the "match" that started the fire that brought down the Swissair MD-11 at Halifax a year and a half ago.

In a March 2 "safety advisory" to U officials, the Transportation Safety Board of Canada (TSB) said, "information has freshly come to light regarding a potential safety deficiency associated with the flight ship's company reading light (usually referred to as a map light) onward MD-11 aircraft".

That's right, a map light. Three are installed in the cockpit of the MD-11 undivided each over the captain's, the first officer's, and the observer's seat. The halogen scaly buds not only produce an intense, white light, they're quite hasty The concern over the map light came about as a spring of the TSB's earlier discoveries in an investigation now into its other year. Early in the wreckage regaining effort, it was evident that the thermal acoustic insulation blankets upon the accident airplane, which are guarded with a flammable metalized Mylar film (metalized polyethylene teraphthalate), had toasted That discovery led to a fleetwide effort to extract the metalized Mylar insulation in all Douglas-built aircraft. Swissair l the industry in this effort, being the first carrier to replace the metalized Mylar in its MD-11 arm of the sea with a more flame resistant materiel called Tedlar (see ASW, Nov. 15 1999)

During the replacement work forward the first aircraft, observed on the TSB, Swissair technicians noted that the intermissioned map lights were installed in so a way that they expressed against the insulation. We are informed that the Mylar was erect to be slightly burned. Similar damage was raise on other Swissair aircraft.

united with these dismaying discoveries, investigators also were analyzing the pattern of electrical anomalies recorded upon the accident airplane's flight data recorder (FDR) Careful analysis of these anomalies and of the wiring circuitry pointed to the left side of the cockpit, which brought attention to the map light across the captain's seat. A fire beginning where the map light crushed against the metalized Mylar, and spreading across the top of the cockpit between the ceiling and exterior skin, seemed to "fit" the data forward the FDR - the random neuronal firings of the airplane's dying computer "brain," as it were. If the map light was the match, the metalized Mylar insulation serv as the tinder.

The TSB is stopping short of declaring the map light as the ignition source, further Boeing has issued an Alert Service Bulletin (No. MD11-33A069) and the U Federal Aviation Administration (FAA) appears sure to issue an airworthiness directive (AD) making the manufacturer's Alert SB mandatory. That FAA action will bring the number of AD's issued forward MD-11 systems, mostly electrical, to 47 since the generation 1998 crash (see ASW, March 6)

Industry sources are praising the TSB's dogged search for the ignition source. Its reconstruction of the fire propagation pattern supported the analysis of electrical anomalies. The electrical inquiry focused attention upon the left side of the cockpit -- and forward the map light. The map light remains a "possible" ignition source, on the other hand getting this far is nonetheless a monumental achievement.

The Map Light as Possible Culprit

Extracts of TSB Letter:

About a dozen MD-11 aircraft from pair operators were inspected. The discrepancies that were discovered included the following:

Several map lights exhibited cracks in the plastic-like protective defends located over the top of the positive terminal of the lamp.

forward some lights, it was evident that these cracks had been repaired.

In single in kind instance, the cover that is normally located in succession the top of the positive terminal was partially missing and the positive terminal strip exhibited melting/arcing damage.

onward a number of map lights, the insulating material covering the ring terminal connectors also exhibited heat deformation.

The MPET-cover (metalized Mylar) insulation material was construct pressed against the back of many fixtures. The damage to the metalized Mylar insulation blankets appeared to ensue from mechanical and thermic meanings of the map light.

Source: TSB

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