Definition
A field on the electronic flight display (or its associated control panel) where the pilot enters the frequency or station identifier of a Distance Measuring Equipment ground station, allowing the avionics to interrogate that station and display slant-range distance to it.
Plain English
It is the small input box on your cockpit display where you type in the DME station you want to measure distance from.
Context Anchor
Seen on electronic instrument displays when checking or setting the source for a distance readout.
Derivation
DME stands for Distance Measuring Equipment, the ground-based system that returns slant-range distance to the aircraft. 'Tuning window' comes from radio practice, where 'tuning' means selecting a frequency and 'window' refers to the on-screen field where that selection is made.
Why Pilots Care
Correct station selection supplies accurate slant-range distance information used for position fixes and approach timing.
Intuition Check
“Window” does not mean a physical window in the airplane. Here it means a small labeled area on an electronic display; “tuning” means selecting the station or channel the DME will use.
Example Sentence 1
Before starting the approach, the pilot entered the identifier for the airport's DME station into the DME tuning window so the distance display would update.
Example Sentence 2
After the DME tuning window locked onto the station, the display showed 8.4 nautical miles to the waypoint.