What is "lnav"

Lateral navigation (LNAV) refers to navigating over a ground track with guidance from an electronic device which gives the pilot (or autopilot) error indications in the lateral direction only and not in the vertical direction. In aviation lateral navigation is of two guidance types: linear guidance and angular guidance. Linear means that the left and right deviations of the aircraft are available as a distance of the aircraft from the desired ground track to its actual position on either side of the desired track. In angular guidance, the error indication is given in degrees of angle from the desired line relative to a ground-based navigation device. To provide an illustration, as the aircraft approaches the ground device with a constant angular error, its distance to the desired ground line decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses lateral navigation) is implied to be a GPS-based approach and to have linear lateral guidance. A VOR based approach will have angular lateral guidance.