Definition
The remaining distance along the approach path from the aircraft's current position to the point of intended landing on the runway. On an Instrument Landing System (ILS) approach, this distance is indicated by passage over marker beacons or by DME readouts referenced to the runway threshold or touchdown zone.
Plain English
How far the aircraft still has to fly before it reaches the spot on the runway where it is supposed to touch down.
Context Anchor
Seen in instrument approach system descriptions, especially where ground equipment provides distance information during the final part of an approach.
Derivation
“Distance” means how far apart two points are. “Touchdown” in aviation means the point where the aircraft’s wheels first contact the runway. Together, “distance-to-touchdown” means the remaining distance to the runway landing point, not just distance to the airport in general.
Why Pilots Care
Enables accurate descent planning, aircraft configuration timing, and maintenance of situational awareness on final approach.
Intuition Check
Do not read “touchdown” as the exact spot where your wheels will actually touch. Here it means a reference landing point or landing area on the runway used by the approach system.
Example Sentence 1
Crossing the outer marker gave the crew a clear distance-to-touchdown reference and confirmed they were on profile.
Example Sentence 2
Passing the outer marker, the distance-to-touchdown was eight nautical miles.