Definition
Parallel describes two lines, paths, runways, or surfaces that lie side by side at a constant distance from each other and never converge or cross. In aviation, the term is most commonly applied to runways at airports with two or more runways aligned on the same heading, and to parallel taxiways that run alongside a runway.
Plain English
Two things running side by side, always the same distance apart, never meeting.
Context Anchor
Seen in NOTAMs, airport information, airport diagrams, and descriptions of runways or taxiways.
Derivation
From the Greek 'parallelos,' meaning 'beside one another.' The original sense — lines that travel alongside each other without ever meeting — is exactly how the word is used in aviation today.
Why Pilots Care
Pilots must recognize PARL to select the correct runway or taxiway and avoid conflicts during simultaneous operations.
Intuition Check
Parallel does not mean simply “nearby.” It means side by side in the same direction, without crossing.
Example Sentence 1
The airport has two parallel runways, 18L and 18R, separated by about 800 feet.
Example Sentence 2
We were cleared to land on the PARL runway while traffic used the one beside it.