Definition
A low-melting-point fusible alloy made of bismuth, lead, tin, and cadmium that melts at approximately 158°F (70°C). In aviation, it is used as the temperature-sensitive plug in fire extinguisher bottles and other thermal release devices, where it melts at a known temperature to release contents or trigger a safety function.
Plain English
A special metal mixture that melts at a low temperature. Aviation uses it as a built-in safety trigger — when things get too hot, the metal melts and lets something happen automatically, like releasing a fire bottle's contents.
Context Anchor
Seen in aircraft maintenance discussions of fire, overheat, or heat-release devices.
Derivation
Named after Barnabas Wood, the American dentist and metallurgist who developed the alloy in 1860. Knowing the name is just a person's name (not a description) prevents the reader from looking for hidden meaning in 'wood.'
Why Pilots Care
If a fire bottle is exposed to excessive heat on the ground or in flight, the Wood's Metal plug melts and discharges the agent overboard through a thermal relief port. A missing or discolored red disc on the side of the aircraft is the visual indication that this has occurred — and that the bottle is empty.
Intuition Check
Do not read Wood'S Metal as a metal made from wood. Here, Wood is a person's name, and the term means a special metal mixture that melts easily.
Example Sentence 1
During the preflight walkaround, the pilot checked that the red thermal discharge indicator was intact, confirming the Wood's Metal plug in the fire bottle had not melted.
Example Sentence 2
Wood's metal served as a reliable temperature fuse in the aircraft's early fire suppression unit.