Definition
A shielded aircraft spark plug with a sealed, weatherproof terminal end that uses a resilient grommet to keep moisture out of the connection between the ignition lead and the plug. It replaced the older open-terminal design and accepts an all-weather ignition harness lead.
Plain English
A spark plug built so that water and moisture cannot get into the wire connection on top of it. The seal keeps the ignition system working reliably in rain, humidity, and temperature changes.
Context Anchor
Seen in aircraft piston-engine ignition system maintenance, especially when inspecting spark plugs and ignition leads.
Derivation
Called 'all-weather' because the sealed terminal allows the plug to perform reliably in all weather conditions, unlike earlier open-terminal plugs that could misfire when moisture got into the connection.
Why Pilots Care
Ensures consistent engine ignition and prevents power loss when flying or operating in wet or humid conditions.
Analogy
It is like using a weatherproof outdoor electrical connector instead of leaving the connection exposed to rain and dirt.
Intuition Check
Do not read “all-weather” as “approved for flying in all weather.” Here it means the spark plug’s electrical connection is sealed and protected from moisture and contamination.
Example Sentence 1
The mechanic installed all-weather spark plugs along with a matching all-weather ignition harness during the engine overhaul.
Example Sentence 2
After the aircraft sat outside overnight in heavy fog, the all-weather spark plugs allowed an immediate engine start.