Definition
On a GPS instrument approach, the gradual narrowing of the receiver's allowable course deviation (CDI sensitivity) as the aircraft transitions from the en route or terminal phase into the approach phase. The full-scale deflection limits tighten progressively so that small lateral errors produce larger needle movement closer to the runway.
Plain English
As you get closer to the runway on a GPS approach, the GPS automatically becomes more sensitive to how far off course you are. The same needle movement now represents a much smaller distance off the centerline, so you have to fly more precisely.
Context Anchor
Seen in GPS instrument approach discussions, especially when the receiver changes from wider en route or terminal guidance to tighter approach guidance.
Derivation
From 'ramp,' meaning a gradual slope or transition, plus 'down,' indicating reduction. Together it describes a smooth, sloped reduction in the sensitivity scale rather than an abrupt switch.
Why Pilots Care
Provides increasingly precise lateral guidance without pilot action, reducing the chance of large course corrections near the runway.
Intuition Check
Ramp-down does not mean the airplane is descending down a ramp. Here it means the GPS display is gradually changing to a tighter, more precise scale.
Example Sentence 1
As the aircraft passed the final approach fix, the GPS completed its ramp-down to approach sensitivity, and small heading deviations began producing noticeable CDI movement.
Example Sentence 2
The pilot monitored the approach and noted the ramp-down had completed before reaching the missed approach point.