Approach Applications which are classified as RNP Approach (APCH) in accordance with ICAO Doc 9613 Performance Based Navigation (PBN) Manual (and ICAO state Letter SP 65/4-10/53) give access to minima (on an instrument approach procedure) designated as:
- LNAV (Lateral Navigation), a Non-Precision or 2D Approach with Lateral only navigation guidance provided by GNSS and an Aircraft Based Augmentation System (ABAS). Receiver Autonomous Integrity Monitoring (RAIM) is a form of ABAS. Lateral guidance is linear with accuracy to within +/- 0.3 NM parallel to either side of the final approach track.
- LNAV/VNAV (Lateral Navigation / Vertical Navigation)
This is a 3D Approach Procedure with Vertical Guidance (APV). The lateral navigation guidance is provided by GPS and Aircraft Based Augmentation Systems (ABAS) such as RAIM in the same way as for LNAV. The vertical guidance is provided by a Barometric Altimeter. This type of approach is commonly known as APV/Baro VNAV. Lateral guidance is normally linear with accuracy to within +/- 0.3 NM parallel to either side of the final approach track. Some aircraft systems may provide angular guidance, however, and pilots should be aware of the display format of their system.
Vertical guidance derived from the barometric data in the Flight Management System (FMS) is based on normal altimetry and any displacement from the indicated glidepath represents the same altitude error throughout the final approach. This is fundamentally different from the angular indications such as on an ILS glidepath.
- LPV (Localiser Performance with Vertical Guidance): an Approach Procedure with Vertical Guidance (APV). The Lateral and Vertical guidance is provided by GPS and SBAS. Lateral and vertical guidance are angular with increasing sensitivity as the aircraft progresses down the final approach track; much like an ILS indication.
Let us first ask if the author was discussing the LPV or LNAV/VNAV scenario.
Both are overrated in LNAV/VNAV MCP selection, but only LPV behaves "like" an ILS and thus could be flown "like" an ILS due to its angular guidance and increasing sensitivity.