Definition
A function of an area navigation (RNAV) system that provides horizontal guidance along a defined flight path, typically using GPS or other approved navigation sources. LNAV controls the aircraft's track over the ground but does not provide vertical guidance.
Plain English
LNAV keeps the aircraft on the correct left-right path along a route or approach. It tells the pilot or autopilot where to go side-to-side, but not how high to be.
Context Anchor
Seen on GPS/RNAV equipment, flight displays, and instrument approach charts, especially on approach minimum lines labeled LNAV.
Derivation
From Latin 'lateralis' meaning 'of the side,' combined with 'navigation.' Lateral here refers to side-to-side movement — left and right of the intended track — as opposed to vertical, which is up and down.
Why Pilots Care
Enables pilots to fly precise lateral paths on approaches, often allowing lower landing minimums and access to more airports in marginal weather.
Analogy
LNAV is like lane guidance on a road map: it helps you stay lined up with the route, but it does not tell you how steep the hill is ahead.
Intuition Check
Do not assume LNAV gives complete approach guidance. LNAV means left-right path guidance; vertical descent guidance must come from another approved source or procedure.
Example Sentence 1
After loading the approach, the pilot armed LNAV so the autopilot would track the final approach course.
Example Sentence 2
With LNAV engaged, the aircraft remained centered on the airway all the way to the initial approach fix.