Of the current RNP designations, RNP-4 is the specification designed for oceanic and remote continental navigation applications. While RNP-10 and North Atlantic High Level Airspace (the old MNPS) are also used, they are not true Performance Based Navigation standards. (We can expect them to go away in the future.)
As of late 2020, only a handful of places in the world say RNP-4 is required but they all have work arounds in place if you are RNP-10 authorized. If you plan on oceanic or remote operations, you will need an LOA when operating under 14 CFR 91. If you are operating under 14 CFR 135, you will need OpSpec B036.
Everything here is from the references shown below, with a few comments in an alternate color.
[ICAO Doc 7030, §MID/ASIA, ¶126.96.36.199.2] For flights on designated controlled oceanic routes or areas within the Auckland Oceanic, Brisbane, Fukuoka, Honiara, Melbourne, Nauru, New Zealand and Port Moresby FIRs, a longitudinal separation minimum of 55.5 km (30 NM) derived by RNAV may be applied between RNAV-equipped aircraft approved to RNP 4 or better, in accordance with the provisions of the PANS-ATM, 188.8.131.52.
[ICAO Doc 7030, §PAC, ¶184.108.40.206.2] For flights on designated controlled oceanic routes or areas within the Anchorage Arctic, Anchorage Continental, Anchorage Oceanic, Auckland Oceanic, Nadi, Oakland Oceanic and Tahiti FIRs, a longitudinal separation minimum of 55.5 km (30 NM) derived by RNAV may be applied between RNAV-equipped aircraft approved to RNP 4 or better, in accordance with the provisions of the PANS-ATM, 220.127.116.11.
In both the Asia and Pacific instances, the 30 NM longitudinal separation "may be applied." If you do not have RNP-4 authorization the following PANS-ATM provisions are cited:
[ICAO Doc 4444, ¶18.104.22.168] LONGITUDINAL SEPARATION MINIMA BASED ON DISTANCE USING RNAV WHERE RNP IS SPECIFIED
22.214.171.124.2.2 Direct controller-pilot communications shall be maintained while applying a distance-based separation minima. Direct controller-pilot communications shall be voice or CPDLC. The communication criteria necessary for CPDLC to satisfy the requirement for direct controller-pilot communications shall be established by an appropriate safety assessment.
126.96.36.199.3 Longitudinal distance-based separation minima in an RNP RNAV environment not using ADS
188.8.131.52.3.1 For aircraft cruising, climbing or descending on the same track, the following separation minimum may be used:
|Separation minimum||RNP type||Communication requirement||Surveillance requirement||Distance verification requirements|
|93 km (50NM)||10||Direct controller-pilot communications||Procedure position reports||At least every 24 minutes|
184.108.40.206.2 The following separation minima may be used for aircraft cruising, climbing or descending on:
a) the same track; or
b) crossing tracks provided that the relative angle between the tracks is less than 90 degrees.
|Separation minimum||RNP type||RCP||RSP||Maximum ADS periodic reporting interval|
|93 km (50NM)||10||240||180||27 minutes|
|93 km (50NM)||4||240||180||32 minutes|
|55.5 km (30NM)||2 or 4||240||180||12 minutes|
|5 minutes||2 or 4 or 10||240||180||14 minutes|
If you do not have ADS and are not RNP-4 authorized, the controllers have the option of accepting you but using increased separation standards provided: you are RNP-10 qualified, you are in direct communications with the controller, and the controller has the capability of intervening within 4 minutes.
[ICAO Doc 9613, Volume II, Part C,¶220.127.116.11]
18.104.22.168.1 Accuracy: During operations in airspace or on routes designated as RNP 4, the lateral TSE must be within ±4 NM for at least 95 per cent of the total flight time. The along-track error must also be within ±4 NM for at least 95 per cent of the total flight time.
22.214.171.124.2 Integrity: Malfunction of the aircraft navigation equipment is classified as a major failure condition under airworthiness regulations (i.e. 10–5 per hour).
126.96.36.199.3 Continuity: Loss of function is classified as a major failure condition for oceanic and remote navigation. The continuity requirement is satisfied by the carriage of dual independent long-range navigation systems (excluding SIS).
188.8.131.52.4 On-board performance monitoring and alerting: The RNP system, or the RNP system and pilot in combination, shall provide an alert if the accuracy requirement is not met, or if the probability that the lateral TSE exceeds 8 NM is greater than 10–5.
184.108.40.206.5 SIS: If using GNSS, the aircraft navigation equipment shall provide an alert if the probability of SIS errors causing a lateral position error greater than 8 NM exceeds 10–7 per hour.
Note.— Compliance with the on-board performance monitoring and alerting requirement does not imply an automatic monitor of FTE. The on-board monitoring and alerting function should consist at least of a NSE monitoring and alerting algorithm and a lateral deviation display enabling the crew to monitor the FTE. To the extent operational procedures are used to monitor FTE, the crew procedure, equipment characteristics, and installation are evaluated for their effectiveness and equivalence as described in the functional requirements and operating procedures. PDE is considered negligible due to the quality assurance process (1.3.6) and crew procedures (1.3.4).
[ICAO Doc 9613, Volume II, Part C,¶220.127.116.11] It is important to understand that additional requirements will have to be met for operational authorization in RNP 4 airspace or on RNP 4 routes. Controller-pilot data link communications (CPDLC) and automatic dependent surveillance — contract (ADS-C) systems will also be required when the separation standard is 30 NM lateral and/or longitudinal. The on-board navigation data must be current and include appropriate procedures.
This is a potential "gotcha" in the works. You can have an OpSpec/MSpec/LOA for RNP-4 authorization without CPDLC and ADS. (Some POIs will not permit this, but some will.) There are locations in the world where the requirement for RNP-4 authorization assumes CPDLC and ADS.
[AC 90-105A, App. F, ¶F.2]
Note: RNP 4 operations are based on Global Positioning System (GPS) positioning. Positioning data from other types of navigation sensors may be integrated with the GPS data provided it does not cause position errors exceeding the Total System Error (TSE) budget. Otherwise, means should be provided to deselect the other navigation sensor types.
Note: Previous approvals under FAA Order 8400.12C, Required Navigation Performance 10 (RNP 10) Operational Authorization, and FAA Order 8400.33, Procedures for Obtaining Authorization for Required Navigation Performance 4 (RNP-4) Oceanic and Remote Area Operations, are still valid for these operations. Operators must ensure their operations remain consistent with the performance and functional requirements of this AC.
[AC 90-105A] Parts 91K, 121, 125, 129, and 135 Operators. Title 14 CFR parts 91K, 121, 125, 129, and 135 operators receive approval to fly RNP operations as described in this AC via operations specifications (OpSpecs), management specifications (MSpecs), or LOAs as follows:
[FAA Order 8900.10 Vol 3, Chapter 18, §B036, ¶k)] OpSpec/MSpec Entries.
Figure: Limitations Extract, from G450 Airplane Flight Manual, §1-03-10, ¶13.]
Advisory Circular 90-105A, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Oceanic and Remote Continental Airspace, 3/7/2016, U.S. Department of Transportation
FAA Orders 8400 and 8900
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, October 2016
ICAO Doc 4444, Amendment 9 to the PANS-ATM, 15 June 2020
ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2008
ICAO Doc 9613 - Performance Based Navigation (PBN) Manual, International Civil Aviation Organization, Fourth Edition, 2013
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