Understanding LNAV Approaches in Aviation

What is an LNA Approach?

An LNA (Lateral Navigation) approach is a non-precision instrument procedure offering lateral (left-right) guidance to the runway centerline.

Its defining characteristic is the lack of vertical guidance. Pilots must manage their own descent using a series of published step-down altitudes to clear obstacles.

While limited to lateral guidance, LNA approaches enhance safety with precise, repeatable tracking and expand airport accessibility.

Key Features of LNA Approaches

Understanding Minimum Descent Altitude (MDA)

The Minimum Descent Altitude (MDA) is a critical safety floor on an LNA approach—it represents the the lowest altitude a pilot is permitted to descend to on instruments alone.

Upon reaching the MDA, the pilot must level the aircraft and maintain that altitude.

If a pilot identifies the runway environment before reaching the Missed Approach Point (MAP), they can descend to land.

LNA vs. LPV: Key Differences

| Feature | LNA | LNA/VSAV | LPs |
|—|—|—|—|
| Guidance | Lateral Only | Lateral & Vertical | Lateral & Vertical (ILS-like) |
| Type | Non-Precision | Approach with Vertical Guidance (APV) | Approach with Vertical Guidance (APV) |
| Vertical Source | None (Pilot Managed) | Barometric Altimetry (Bar-VNAV) or WAS | WAS |
| Minimums | MDA (~400 ft AGL) | DA (>250 ft AGL) | DA (as low as 200 ft AGL) |
| Procedure | Step-down descent (“Dive and Drive”) | Continuous descent path | Continuous, precise glide path |

Equipment and Technology for LNA Approaches

Flying an LNA approach requires an aircraft to be equipped with a certified GPS or WAS-enabled navigation system for lateral guidance.

Signal integrity is ensured by Receiver Autonomous Integrity Monitoring (RAIL), a GPS receiver function that constantly verifies the health of satellite signals and alerts the pilot to potential errors.

Many aircraft integrate GPS with an autopilot’s LNA mode, which automatically flies the lateral course.

Regulatory Standards for LNA Approaches

The Federal Aviation Administration (FAA) classifies LNA as a non-precision, GPS-based instrument approach providing lateral guidance only.

Common Questions About LNA Approaches

What is the primary purpose of an LNA approach?

LNA approaches provide precise lateral GPS guidance to a runway, serving as a modern equivalent to older non-precision procedures like VOR or localizer-only approaches.

Why is there no vertical guidance?

LNA is the most basic form of GPS approach, designed solely for reliable horizontal positioning.

How low can I descend on an LNA approach?

Pilots can descend to the published Minimum Descent Altitude (MDA), typically around 400 feet above the runway.

What happens if I can’t see the runway at the MDA?

If the runway environment is not in sight upon reaching the Missed Approach Point (MAP), the pilot must immediately execute the published missed approach procedure.