It is easy to get confused by the variety of published minimums on today’s GPS approach procedures. Selecting the right one for the conditions and aircraft equipment is extremely important because each are fundamentally different. Let’s start by reviewing the different types of minimums followed by practical application of each.
LNAV – Think of this minimum as the same found on your typical VOR or LOC approach. It is a classic ‘dive and drive’ approach descending from the FAF to the MDA with no vertical guidance. Once reaching the MDA the pilot is expected to level off and hopefully acquire the runway environment visually to land using normal maneuvering.
LNAV/VNAV (LNAV+V) – These minimums add an additional layer of safety by computing a VDA, or visual descent angle, from the FAF to the TCH. This means you can fly a constant angle stabilized approach similar to an ILS. There is no vertical path signal but depending on your aircraft equipment the GPS receiver can calculate the vertical path using information coded in the approach data.
LPV – Lateral and Precision Vertical minimums can be used by WAAS receivers which improve position accuracy and provide both lateral and vertical guidance, much like an ILS. This is why LPV are considered precision approaches whereas the other minimums are not, despite the vertical guidance.
You are flying a WAAS-equipped aircraft planning on an LPV approach. You have a 15 knot tailwind on final so you plan to circle and land on the opposite runway. You can fly the LPV approach to circling minimums but must maintain the Circling MDA throughout the visual maneuver until you are in a position to land using normal maneuvering.
You are flying a WAAS-equipped aircraft approaching the FAF but LPV is not annunciated on the GPS display. You may continue the approach using LNAV minimums provided the RAIM is adequate and published LNAV minimums exist for the procedure.
You are flying a non-WAAS aircraft but the equipment has descent planning features. You may use the VNAV functions to calculate a descent rate FOR GUIDANCE ONLY. The LNAV minimums and any step-down fixes must be obeyed so be careful and cross reference the profile section to ensure step-downs are met.
Always refer to the Operating Handbook Supplement and GPS Pilot Guide to verify the capabilities for the specific equipment you use.