Definition
The temperature of the gases in a turbine engine measured at a point between two of the turbine wheels (stages), rather than at the turbine inlet or exhaust. ITT is used as an operating limit and as a primary indicator of engine condition during start, acceleration, and steady running.
Plain English
It is the temperature of the hot gases passing through the middle of the turbine section of a jet or turboprop engine. Pilots watch this number to make sure the engine is not running too hot.
Context Anchor
Seen on turbine-engine instrument panels, engine-start checks, takeoff power checks, climb power settings, and engine limitation charts.
Derivation
Interstage comes from Latin inter (between) and stage (a step or level). The temperature is measured between the stages of the turbine, which is exactly what the name describes.
Why Pilots Care
Pilots watch this reading to detect overheating, confirm proper engine operation, and avoid exceeding temperature limits that can damage turbine blades.
Intuition Check
Do not read this as the outside temperature or the general temperature of the whole engine. It is a specific internal gas temperature measured between turbine stages.
Example Sentence 1
During the engine start, the pilot watched the ITT closely to make sure it stayed below the limit.
Example Sentence 2
An unusually high interstage turbine temperature after landing prompted the crew to request an engine inspection.