RNAV (GPS) Approaches: LPV, LNAV and LNAV/VNAV

RNAV (GPS) Approaches: LPV, LNAV and LNAV/VNAV

Modern GPS-based approaches have revolutionized instrument flying, offering precision-like guidance to thousands of runways that never had ILS capability. Understanding the differences between LPV, LNAV/VNAV, and LNAV approach minimums isn't just academic—it directly affects your minimums, obstacle clearance, and decision-making on every approach.

Understanding the Minima Lines

When you brief an RNAV (GPS) approach chart, you'll typically see multiple lines of minimums. These aren't interchangeable options—they represent different levels of navigation performance your equipment can provide.

LPV (Localizer Performance with Vertical Guidance) provides the lowest minimums, often matching ILS decision heights of 200 feet. Despite the name, LPV has nothing to do with localizers. It uses WAAS (Wide Area Augmentation System) corrections to achieve lateral sensitivity that narrows as you approach the runway—just like an ILS—and provides angular vertical guidance. The key difference from ILS is that LPV guidance comes entirely from satellites, not ground-based equipment.

LNAV/VNAV offers vertical guidance without WAAS, using barometric altitude (from your altimeter) for the vertical component. These minimums are typically higher than LPV, often 300-400 feet, because the system lacks the precision of WAAS-corrected satellite geometry.

LNAV provides lateral-only guidance with no glidepath. You'll fly a dive-and-drive approach using step-down fixes, similar to a VOR approach. LNAV minimums are the highest, frequently 400-500 feet or more, and result in an MDA (minimum descent altitude) rather than a DA (decision altitude).

What Your Avionics Can Actually Fly

Here's where pilots make critical mistakes: your GPS navigator determines which minimums you can use, not your preference or the weather.

To fly LPV approaches, you need WAAS-certified GPS equipment. Most GPS navigators installed after 2007 have this capability, but older units like the GNS 430 (non-WAAS) do not. Check your AFM supplement—if it says "LPV" in the approved approach types, you're good to go.

For LNAV/VNAV, you need either WAAS or a system that integrates GPS with your barometric altimeter (called baro-VNAV). However, baro-VNAV has temperature limitations. When temperatures fall outside the charted range, LNAV/VNAV minimums become unavailable, and you must use LNAV minimums instead.

LNAV is available to any IFR-certified GPS navigator, including non-WAAS units. It's your backup when nothing else works.

Flying the Approach: Practical Differences

The flying technique varies significantly between these approach types. With LPV, fly it exactly like an ILS: intercept the glidepath from below, maintain a constant descent rate, and execute a missed approach at DA if you don't have the required visual references. The glidepath is your friend—stay on it.

LNAV/VNAV feels similar to LPV in the cockpit since you're following a glidepath indication. However, remember that vertical guidance comes from your altimeter. If you haven't set the current altimeter setting, or if temperatures are extreme, your vertical path may be unreliable. Always verify you're at the charted altitudes at each waypoint.

LNAV requires old-school technique. Brief your step-down fixes, calculate your descent rate to arrive at MDA with enough distance to identify the runway environment, and level off at MDA until you either see the runway or reach the missed approach point. Don't duck below MDA early—that's a violation and dangerous.

Common Mistakes and Pro Tips

The most frequent error is descending below LPV or LNAV/VNAV minimums when the glidepath continues below DA. Unlike an ILS glideslope that remains reliable through touchdown, GPS glidepaths lose their obstacle clearance guarantee below DA. When you reach minimums, the glidepath becomes irrelevant—fly visually or go missed.

Another mistake is attempting to "step down" on LPV approaches. The procedure is designed for continuous descent. Leveling off at intermediate altitudes increases workload and defeats the approach's efficiency.

Always check NOTAMs for GPS outages or WAAS unreliability. Unlike ground-based navaids that fail obviously, GPS degradation can be subtle. If your navigator downgrades from LPV to LNAV during the approach, you must use LNAV minimums—even if you continued the approach.

Finally, brief all available minimums before the approach. If LPV isn't available due to equipment or NOTAM restrictions, know your backup plan before you're heads-down in IMC.

--- *Reference and study only — not for operational use. Always follow your POH/AFM, current regulations and a qualified instructor.*