Aviation Investigation Report A98H0003
2.12 Flight Crew Reading Light (Map Light) Installation
The design deficiencies of the Hella map light resulted in the potential for electrical arcing in typical in-service conditions. Normal rotation of the lens housing allowed contact between the insulating protective cap and the carrier frame; over time, usage would result in damage to the protective cap exposing the positive terminal metal contact spring. This situation provided an opportunity for the exposed metal contact spring to arc to the carrier frame. The design also created at least three additional opportunities for electrical arcing, including during bulb replacement maintenance activity.
Also, the map light installations at the pilot and co-pilot positions in the MD-11, were located in confined areas near, or in direct contact with, combustible materials that could exacerbate the consequences of any potential arcing. The overheat damage observed on several MPET-covered insulation blankets examined in other MD-11s, reflected the heat build-up behind the map lights. The combination of radiant heat and close proximity would increase the probability of igniting the MPET-covered insulation blankets during an arcing event.
The map lights were not involved with the origin of the SR 111 fire; however, the deficiencies found in both the map light design and its MD-11 installation presented unacceptable risk. These safety deficiencies are being eliminated by the follow-up actions underway (see Section 4.1.4).
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