VNAV = Vertical Navigation. LNAV = Lateral Navigation.
LNAV is illuminated when pushed. Arms or engages LNAV mode. If armed, LNAV is annunciated in white on primary flight displays. Active roll is not affected. If LNAV is armed and the airplane is above 50ft and within 2.5 NM of the active leg, LNAV engages.
Thats a few...
Now VNAV...If VNAV is armed and the airplane is above 400ft with the FMC (flight management computer) Perf Init page completed (Performance Initialisation), LNAV in engaged. Thus, VNAV SPD, VNAV PATH, or VNAV ALT is annunciated on the PFD's (primary flight displays) in green. When VNAV is engaged, the system commands pitch to maintain FMC altitude...
Again, a few...
This is 747. I presume it is the same for Airbus?
Smooth skies
