Definition
In satellite navigation, ranging sources are the satellites whose signals a GPS receiver uses to calculate distance (range) from each satellite to the aircraft. By measuring the travel time of signals from multiple ranging sources, the receiver determines the aircraft's position, altitude, and time.
Plain English
The satellites that a GPS receiver listens to in order to figure out how far away each one is. The receiver uses those distances to work out exactly where the aircraft is.
Context Anchor
Seen in instrument navigation and NextGen discussions, especially when describing how modern systems determine position for published instrument procedures.
Derivation
From 'range' meaning distance to a point. A ranging source is literally a source the receiver uses to measure range. Knowing this makes the term self-explanatory: each satellite is a source of range information.
Why Pilots Care
They allow accurate position fixes for RNAV routes and approaches without needing traditional visual or radar references.
Grounding Statement
Picture the aircraft comparing its distance from several known signal sources to pin down its own location.
Intuition Check
Ranging sources does not mean a variety of sources. Here, ranging means sources used to measure distance.
Example Sentence 1
The approach was downgraded because the receiver lost one of its ranging sources and could no longer compute a valid position with full integrity.
Example Sentence 2
DME stations served as ranging sources to verify distance to the final approach fix.