Open a modern instrument approach chart titled "RNAV (GNSS)" or "RNP" and you will see several lines of minima: LNAV, LNAV/VNAV, LP, LPV. Each one is a different level of satellite-based guidance. This guide explains what they mean and how pilots choose between them.
RNAV and RNP in one paragraph
Area navigation (RNAV) lets an aircraft fly any desired path using waypoints, instead of flying directly between ground beacons. Required Navigation Performance (RNP) adds on-board monitoring and alerting: the system warns the crew if it cannot meet the required accuracy. Under ICAO's Performance-Based Navigation (PBN), most approaches labelled RNAV (GNSS) are RNP APCH procedures.
The lines of minima
LNAV: lateral navigation
GNSS provides lateral guidance only. The approach is flown to a Minimum Descent Altitude (MDA), like a non-precision approach.
LNAV/VNAV: lateral and vertical
Adds vertical guidance, usually from barometric VNAV (or SBAS). Flown to a Decision Altitude (DA). Because baro-VNAV depends on the altimeter, cold temperatures affect it, and charts may show temperature limits.
LP: localizer performance
Uses SBAS to give a precise, angular lateral guidance similar to a localizer, but without approved vertical guidance. Flown to an MDA.
LPV: localizer performance with vertical guidance
Uses SBAS for both lateral and vertical guidance, with accuracy similar to an ILS. LPV minima can be as low as about 200 ft above the runway, comparable to an ILS Category I approach.
RNP AR: authorisation required
Designed for difficult terrain or airspace. These approaches can include curved paths and very tight accuracy values, and need special aircraft equipment, crew training and operator approval.
Watch: RNAV approaches in 60 seconds
SBAS and GAGAN
Satellite-Based Augmentation Systems correct GPS errors and monitor integrity, making LP and LPV possible. India's SBAS is GAGAN (GPS Aided GEO Augmented Navigation), developed by ISRO and the Airports Authority of India. It is what allows LPV approaches to be introduced at Indian airports. Read more in our article on SBAS if you want the background.
Which minima can the crew use?
It depends on the aircraft's equipment and approval, the availability of SBAS or baro-VNAV, and NOTAMs. The crew briefs the lowest line of minima they are equipped and approved for, and knows which line to fall back to if a function is lost.
Exam summary
- LNAV and LP: no vertical guidance, flown to an MDA.
- LNAV/VNAV and LPV: vertical guidance, flown to a DA.
- LP and LPV need SBAS; LNAV/VNAV usually uses baro-VNAV.
- RNP AR: special approval, tight tolerances, possible curved paths.
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