Definition
A temperature-sensing probe installed in an aircraft system to measure the temperature of a fluid, gas, or surrounding air. The bulb contains a sensing element — commonly a resistance wire or a thermocouple junction — whose electrical properties change with temperature. This change is read by a cockpit gauge or by an engine monitoring system and displayed as a temperature value.
Plain English
A small probe that sits in the oil, fuel, air, or other place you want to measure, and sends a temperature reading to a gauge in the cockpit.
Context Anchor
Seen in aircraft instrument systems, engine temperature indications, oil temperature systems, and outside-air temperature sensing.
Derivation
Called a 'bulb' because early sensors had a rounded, bulb-shaped tip housing the sensing element, similar in shape to the bulb of a household thermometer. The name stuck even though modern probes are often slim and cylindrical.
Why Pilots Care
Accurate readings let pilots monitor engine health and avoid overheating damage during flight.
Intuition Check
Do not think of a temperature bulb as a light bulb. Here, bulb means a heat-sensing part of an instrument system.
Example Sentence 1
The mechanic replaced the oil temperature bulb after the cockpit gauge began reading unusually low during cruise.
Example Sentence 2
During cruise the pilot confirmed stable cylinder head temperatures from the bulb sensor data.