Definition
A non-precision GPS-based instrument approach that provides lateral (left/right) course guidance to a runway, but no vertical guidance. The pilot flies the lateral track shown by the GPS and steps down through published minimum altitudes until reaching the Minimum Descent Altitude (MDA), where the runway environment must be in sight to continue to land.
Plain English
A GPS approach that tells you where to fly side-to-side toward the runway, but does not tell you how to descend. You handle the descent yourself using the altitudes printed on the chart.
Context Anchor
Seen on GPS-based instrument approach charts and in IFR alternate planning when checking what kind of approach minimums are available.
Derivation
Lateral comes from the Latin lateralis, meaning 'of the side.' Navigation comes from the Latin navigare, 'to sail or steer a ship.' Together: side-to-side steering guidance, with no up-or-down component.
Why Pilots Care
LNAV allows an approach when vertical guidance is unavailable, but it produces higher minimum descent altitudes and visibility requirements than LPV or ILS.
Intuition Check
LNAV does not mean the system gives all possible GPS guidance. It means lateral guidance only: left and right, not an approved descent path.
Example Sentence 1
The forecast ceiling was below the LNAV/VNAV minimums, so we planned the approach to the higher LNAV MDA instead.
Example Sentence 2
Briefing the plate, she noted the LNAV MDA required an additional 400 feet of ceiling compared with the ILS.