ICAO APPROACH CLASSIFICATIONS FOR GNSS
NPA (non-precision approach)
Only lateral guidance, horizontal alert limit: 0.3 NM. No vertical alert limits. Procedures according to dive and drive principle.
Example: RNP APCH to LNAV minima (described below)
Lateral approaches with vertical guidance (-> still NPA but with vertical guidance)
APV – Baro VNAV
Lateral approach with Barometric vertical guidance.
Examples: RNP APCH to LNAV/VNAV minima (described below)
APV-I
Horizontal alert limit: 40m, vertical alert limit: 50m, decision height: ?300-400ft.
Example: RNP APCH to LPV minima (described below)
LPV200
Equal to APV-I but decision height: 200ft as in CAT-I operations (->still not a precision approach)
Example: RNP APCH to LPV minima (described below)
(CDFA-Technique)
CDFA: Continuous Descent Final Approach (no dive and drive), applicable with all approach types
with vertical guidance (not to be confused with the term Continuous Descent Approach (CDA) which applies primarily before the final approach)
Precision Approach: CAT-I for GNSS
Horizontal alert limit: 40m, vertical alert limit: 15m – 10m, decision height: 200ft
Example: GLS procedures
Precision Approach: CAT-II/III for GNSS
not yet defined in ICAO SARPS
Example: GLS procedures in the future
-> all alert limits given are for the navigation system error (NSE) which is only a part of the TSE (Total System Error). The FTE (Flight Technical Error) is not considered in the above approach classification.
ICAO PBN Specifications/Procedures
RNP APCH to LNAV minima
The primary navigation system is GNSS (GPS/RAIM). Accuracy: The lateral total system error (TSE) and along-track error must be <±0.3 NM for at least 95% of the flight time on the final approach segment (<±1 NM for the initial & intermediate approach segment). Onboard performance monitoring and alerting is required. Only the horizontal navigation is considered (LNAV minima) -> allows 2D non-precision approach (NPA).
-> ability to fly: most commercial airlines and GA partially, however, further approvals necessary
This is a RNAV approach without vertical guidance. It is often called RNAV NPA (other names are RNAV (GNSS) or RNAV (GPS)) and is almost always based on the use of GPS.
RNP APCH to LNAV/VNAV minima
Same than for RNP APCH to LNAV minima but additionally vertical guidance is given by means of barometric altitude determination -> allows 3D lateral approach with vertical guidance (APV-Baro VNAV).
-> ability to fly: most commercial airlines and GA partially, however, further approvals necessary
This procedure is a vertically guided approach that can be flown by modern aircraft with VNAV functionality using barometric inputs. Most Boeing and Airbus aircraft already have this capability meaning that a large part of the fleet is already equipped.
RNP APCH to LPV minima
RNP APCH to LPV minima is a procedure supported by SBAS systems such as WAAS in the US and EGNOS in Europe to provide lateral and vertical guidance. The term LPV stands for localizer performance with vertical guidance. The lateral performance is equivalent to an ILS localizer and the vertical guidance is provided against a geometric path in space rather than a barometric altitude. LPV is of particular interest to a category of users with aircraft that do not have sophisticated FMS based avionics that can perform Baro/VNAV.
-> interest to fly: GA
RNP APCH to LP minima
Lateral guidance same as RNP APCH to LPV minima but no vertical guidance. Comparable to an ILS approach without Glidepath. To be used in mountainous areas if the SBAS availability is insufficient for vertical guidance.
RNP AR APCH procedure (AR: Authorization Required)
The primary navigation system is GNSS (GPS/RAIM) and INS (often multiple GNSS, INS and FMS necessary). Accuracy: The lateral total system error (TSE) and along-track error must be <=0.3 NM for at least 95% of the flight time. (<=1 NM for the initial & intermediate approach segment). Onboard performance monitoring and alerting is required. Procedure is combined with a vertical navigation through Barometric VNAV (LNAV/VNAV minima). In contrary to RNP APCH procedures, RNP AR APCH procedures take advantage of improved aircraft performance. Furthermore, curved paths with a constant radius are possible.
-> ability to fly: commercial airlines partially and GA partially, however, further approvals necessary
RNP AR approaches make use of advanced RNP capabilities of certain modern aircraft to provide better access to runways with terrain or environmental constraints. They use specific obstacle clearance criteria and require a particular RNP approval for the aircraft. RNP AR is designed for the latest, most sophisticated aircraft, capable of PBN and requires a particular kind of safety assessment for operational approval (note that for each procedure, a dedicated approval is necessary for airplane, avionics, crew,…).
