LPV—Precision or not?

We all know an ILS is a precision approach. But there’s much confusion about whether an RNAV (GPS) approach to LPV minimums is. (Spoiler alert: Sometimes …)

BTeter

Friday, August 09, 2024 at 07:17 AM ET

Verified

This FAA diagram nicely shows the various antennas associated with an ILS.

Key Takeaways:

ILS (Instrument Landing System) is a ground-based system using radio signals for lateral and vertical guidance, historically considered the "gold standard" for precision approaches and currently the only option for Category II/III landings.
LPV (Localizer Performance with Vertical Guidance) is a satellite-based approach requiring WAAS-enabled GPS, offering high accuracy and stability comparable to a Category I ILS, without signal bends or false glidepaths.
Despite LPV's superior accuracy, the FAA generally classifies it as an "Approach with Vertical Guidance" (APV) rather than a "precision approach" for operational rules (e.g., alternate airport minimums) primarily due to the lack of a mandatory approach lighting system (ALS).
For pilot certification and currency purposes, however, LPV approaches are now accepted as counting toward precision approach requirements.

See a mistake? Contact us.

Perhaps it’d be best if we first take a broad look at the differences between an ILS and an LPV approach. A significant difference between the ILS and LPV is that the ILS is a ground-based system with several components that operate as a federated system to provide approach guidance. On the aircraft side, you must have a VHF localizer receiver, a UHF glideslope receiver, or a multimode receiver that incorporates both, and a method to determine noted distances from the runway threshold (marker beacon, compass locator, DME, radar, VOR cross radials).

The LPV approach is satellite-based; however, it also requires a ground-based station(s) to determine any errors in the “raw” GPS position and broadcast a correction. The detection of errors in the GPS position is the basis for the wide-area augmentation system (WAAS). GPS errors are also monitored via receiver autonomous integrity monitoring (RAIM), but WAAS makes it redundant. Let’s dig into this in more detail.