Definition
A sealed, flexible metal capsule used inside a true airspeed indicator that expands and contracts in response to changes in outside air pressure, with a built-in mechanism that adjusts its movement to account for changes in outside air temperature. This combined response allows the instrument to convert indicated airspeed into true airspeed automatically as the aircraft climbs or descends through air of varying density.
Plain English
A small sealed metal bellows inside the airspeed instrument that senses both air pressure and air temperature. Because air gets thinner and colder with altitude, the bellows uses both readings to show the airspeed correctly for the conditions outside.
Context Anchor
Seen in discussions of true airspeed indicators and how an airspeed instrument corrects for changes in altitude and temperature.
Derivation
Aneroid comes from the Greek 'a-' (without) and 'neros' (water), meaning 'without liquid' -- it senses pressure without using a liquid like mercury. A bellows is a flexible, accordion-like chamber. 'Temperature-compensated' simply means the device has a built-in adjustment for temperature changes, so its readings stay accurate as the air gets colder or warmer.
Why Pilots Care
Prevents airspeed indication errors caused by temperature extremes, allowing consistent performance data during climbs, descents, or operations in varying weather.
Analogy
Think of a sealed metal squeeze box that expands or contracts as the air around it changes. The instrument uses that small movement to help move the pointer to a more accurate reading.
Grounding Statement
As the airplane climbs into thinner air or flies in warmer air, the bellows helps the instrument adjust for those changing air conditions.
Intuition Check
Temperature-compensated does not mean the bellows measures temperature for the pilot. It means the part is designed so temperature effects are accounted for in the instrument’s movement.
Example Sentence 1
The true airspeed indicator uses a temperature-compensated aneroid bellows so the displayed airspeed remains accurate as the aircraft climbs into colder, thinner air.
Example Sentence 2
On a cold winter flight the pilot relied on the temperature compensation in the aneroid bellows to keep the airspeed reading accurate without manual adjustment.