Definition
LNAV mode is a flight guidance mode in which the autopilot or flight director steers the aircraft laterally (left and right) along a programmed RNAV course defined in the flight management system or GPS navigator. It controls heading and track to follow the magenta line of the active flight plan, including straight legs, course changes at waypoints, and curved path segments where coded.
Plain English
A mode that lets the autopilot fly the side-to-side path you have programmed into the navigation computer, automatically turning at each waypoint to stay on the planned route.
Context Anchor
Seen when flying an area navigation arrival, a route transition, or a loaded flight plan using the autopilot, flight director, or navigation display.
Derivation
Lateral comes from the Latin lateralis, meaning 'of the side.' In flight, lateral guidance refers to side-to-side steering (the horizontal path over the ground), as distinct from vertical guidance (up and down). LNAV therefore means the system handling the horizontal track only.
Why Pilots Care
Enables precise lateral tracking of curved paths and waypoints without ground-based navigation aids.
Intuition Check
Do not assume LNAV mode flies the whole arrival by itself. LNAV is mainly about left-right path guidance, not altitude control.
Example Sentence 1
After takeoff, the crew engaged the autopilot and selected LNAV mode to follow the RNAV departure.
Example Sentence 2
With LNAV active the aircraft tracked the curved path during the STAR transition.