Definition
Segments of airspace along an airway or route where signal coverage from ground-based navigation aids (such as VORs) is unavailable or unusable, leaving the pilot temporarily without that source of electronic course guidance. The FAA evaluates these gaps and may permit them when they are short enough — based on aircraft speed and altitude — that the aircraft can cross them without losing safe navigation continuity, especially when other means (GPS, DME, radar) are available.
Plain English
Stretches along a route where the ground-based navigation signal drops out for a short time. The gap is allowed only if it's small enough that you can fly through it safely before picking up the next signal.
Context Anchor
Seen in instrument procedure and en route chart discussions, especially when a route depends on ground-based navigation signals that may not cover every mile continuously.
Derivation
“Navigation” comes from older words connected with directing a ship or vehicle along a course. “Gap” means a break or opening. Together, the phrase points to a break in reliable navigation coverage along a route.
Why Pilots Care
Pilots must identify these gaps in advance to switch to dead reckoning or other methods and avoid losing situational awareness.
Analogy
It is like driving through a short area with no cell service: the road is still there, but the signal you normally rely on may not be available for that stretch.
Intuition Check
Do not read “gap” as a missing line on the chart or an empty space in the procedure. Here it means a break in usable navigation guidance along part of the route.
Example Sentence 1
The chart review showed a navigational gap between the two VORs, so the crew planned to use GPS to bridge that segment.
Example Sentence 2
Reviewing the plate for navigational gaps helped the pilot plan the transition using time and heading instead of relying on signals.