Definition
A cockpit gauge that displays the temperature of the gases flowing between the stages of a turbine engine, typically measured by thermocouples placed between the compressor turbine and the power turbine. It is used to monitor engine operating temperature against published limits during start, takeoff, climb, and cruise.
Plain English
A gauge that shows how hot the gases are inside the turbine section of the engine, so the pilot can make sure the engine isn't running too hot.
Context Anchor
Seen on the engine instrument panel of many turboprop airplanes, especially during engine start, takeoff, climb, and power changes.
Derivation
Interstage means 'between the stages.' In a turbine engine there are multiple turbine wheels in series, and the temperature is measured at a point between them — hence 'interstage' rather than at the very front or very back of the turbine section.
Why Pilots Care
Pilots monitor it to avoid turbine damage; exceeding temperature limits can cause engine failure or expensive repairs.
Analogy
It is like a temperature gauge for a very hot part of the engine. If the number climbs past the limit, the pilot needs to reduce the heat source before damage occurs.
Intuition Check
Do not read ITT as a general engine temperature. It is a specific temperature measured in the turbine section, and its limits matter especially during starting and power changes.
Example Sentence 1
During engine start, the pilot watched the ITT indicator carefully to make sure the temperature stayed below the start limit.
Example Sentence 2
A gradual rise in ITT during cruise may signal reduced compressor efficiency or a fuel scheduling issue.