Definition
An electrical heating element installed in or attached to the engine block of a reciprocating aircraft engine, used to warm the engine and its oil before starting in cold weather. It is plugged into an external power source on the ground and warms the engine by conduction over a period of hours.
Plain English
A small electric heater fitted to the engine that is plugged in before flight to warm the engine up so it will start more easily and run safely in cold weather.
Context Anchor
Seen in cold-weather operations, winter preflight planning, and aircraft tiedown or hangar procedures before the first engine start of the day.
Derivation
The 'block' is the main metal casing of the engine — the cylinder block. A 'block heater' is simply a heater that warms that block. The name comes straight from automotive use, where the same device has been used for decades on car engines in cold regions.
Why Pilots Care
Cold oil is too thick to circulate properly; a block heater reduces wear, prevents hard starts, and lowers the risk of engine damage on sub-freezing days.
Analogy
A block heater is like an electric blanket for the engine: it does not run the engine, but it takes the worst chill out before you ask the engine to work.
Intuition Check
A block heater is not a cabin heater. It warms the engine before start; it does not make the cockpit comfortable or replace normal cold-weather checks.
Example Sentence 1
After an overnight cold snap, the pilot plugged in the block heater two hours before the planned departure so the engine would start cleanly.
Example Sentence 2
In the morning the oil temperature gauge already showed a safe reading thanks to the block heater.