Aviation Investigation Report A98H0003
1.19.5 Temperature Reference Coupons (STI1-124)
To permit an evaluation of the temperature reached by the hundreds of heat-damaged aircraft pieces, various heat templates or temperature reference coupons were produced in a controlled laboratory environment. The coupons consisted of representative samples of MD-11 aircraft materials, painted in accordance with the original manufacturer's specifications. Each temperature coupon was heated at a fixed temperature for a specified period of time. Temperature reference coupons were produced at 50°F increments for temperatures ranging from 300°F to 1 100°F (149°C to 593°C), and for exposure times of 10, 20, and 30 minutes. Each coupon was characterized by a discolouration of the painted finish that was indicative of the bake temperature and duration of exposure. The effect of immersion in sea water of the heated samples was also determined; at most temperatures the effect on the discolouration was negligible.
Hundreds of pieces of aircraft structure and air conditioning ducting exhibited indications of heat damage. The recovered pieces were compared to the temperature coupons constructed from identical material to determine the approximate temperature and duration of exposure. This information was used to establish heat pattern and temperature distribution within the fire-damaged attic area of the aircraft.
For comparison purposes, metallurgical analysis of temperature coupons and of the hottest recovered aircraft pieces was performed to more closely assess the temperatures reached based on the effect of the heat on the micro-structure of the various samples.
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