Definition
The volume of airspace within which the radio signal from a ground-based navigation aid (such as a VOR, NDB, or DME) is strong enough and reliable enough to be used for navigation. Coverage is limited by the transmitter's power, the type of facility, the receiver's altitude above the station, terrain, and line-of-sight obstructions.
Plain English
The area around a ground navigation station where its signal can actually be received and trusted for navigating. Outside that area, the signal is too weak or unreliable to use.
Context Anchor
Seen in instrument flight planning and chart discussions, especially when an altitude gives obstacle clearance but may not guarantee reception from ground navigation stations.
Derivation
NAVAID is short for navigation aid. 'Ground-based' distinguishes these from satellite-based aids like GPS. 'Signal coverage' simply means the area the signal reaches with usable strength.
Why Pilots Care
It determines how far an aircraft may safely fly off established airways while still relying on ground signals for position awareness.
Analogy
It is like cell phone coverage: being in the general region is not enough. The signal has to reach your exact location strongly enough to be usable.
Intuition Check
Do not read “coverage” as meaning obstacle clearance or route approval. Here, coverage only means the aircraft should be able to receive and use the ground station’s navigation signal.
Example Sentence 1
When choosing an off-route altitude over the mountains, the pilot made sure to stay high enough to remain within the VOR's signal coverage.
Example Sentence 2
Published ORCAs account for reduced ground-based NAVAID signal coverage in remote areas.