2012-02

Required Navigation Performance/Performance-Based Navigation

Effective date: 10 October 2012

Reference:  TAM, Part 2, Chapter 3 and part 3, chapter 2

                  OAM, Chapter 3, Paragraph 314

OPI/Telephone: DTAES 3, 819-939-4810

1.   Purpose

1.1.  The purpose of this document is to:

  1. provide guidelines for the certification, airworthiness and operational approval of Required Navigation Performance (RNP);
  2. specify the principle that RNP to be used on an aircraft is to be subjected to a defined evaluation process;
  3. provide specific guidance material for RNP applications and approvals and establish certification, airworthiness/installation, and operational approval guidance for RNP; and
  4. provide checklists to assist operators, installers and regulators in evaluating RNP implementations.

1.2   This advisory is not mandatory, nor does it constitute a regulation. It describes a means acceptable to the Technical Airworthiness Authority (TAA), but is not the only means to demonstrate compliance with the airworthiness program requirements. The use of the terms “shall”, “must” and “is required/requested to” apply only to applicants who elect to comply with this TAA advisory in order to obtain airworthiness approval.

2.    Applicability

2.1    Technical and Operational Airworthiness Clearance.

2.1.1. This document applies to TAA and Operational Airworthiness Authority (OAA) personnel, Fleet Weapon System Managers (WSMs), Senior Design Engineers (SDEs), Authorized Individuals and the aviation industry. This document provides advisory material that must be considered and applied, as appropriate, to the development and approval of the operational and Technical Airworthiness Clearance of Required Navigation Performance capabilities.

2.1.2. DND/CF's Airworthiness Program requirements (A-GA-005-000/AG-001 – Policy/Management Procedures and Guidelines for the Department of National Defence/Canadian Forces Airworthiness Program), Part 2, Section 1, subsection 6 – “Civil Air Navigation and Communication Requirements” require all Royal Canadian Air Force (RCAF) aircraft to comply with civil navigation rules while operating in civil airspace.

3.    Related material

3.1    Definitions

  1. Aircraft Flight Manual (AFM). For the purposes of this TAA Advisory, the term AFM applies equally to fixed-wing aircraft and rotorcraft. For those fleets that do not have an AFM, those sections of the Aircraft Operating Instructions (AOI) that contain TAA-approved Technical Airworthiness Data (TAWD) can be assumed to be the equivalent of the AFM.
  2. Flight Technical Error (FTE). The accuracy with which the aircraft is controlled as measured by the indicated aircraft position with respect to the indicated command or desired position.
  3. Operating System. Software that controls the execution of programs and that may provide services such as resource allocation, scheduling, input-output control, and data management.
  4. Performance-based navigation (PBN). Area navigation based on performance requirements for aircraft operating along an Air Traffic Service (ATS) route, on an instrument approach procedure or in a designated airspace.

Note:   Performance requirements are expressed in navigation specifications in terms of accuracy, integrity, continuity and functionality needed for the proposed operation in the context of a particular airspace concept. Availability of Global Navigation Satellite System (GNSS) Signal-In-Space (SIS) or some other navigational aid (NAVAID) infrastructure is considered within the airspace concept in order to enable the navigation application.

  1. Area navigation (RNAV) system. A navigation system which permits aircraft operation on any desired flight path within the coverage of station-referenced NAVAIDs or within the limits of the capability of self-contained aids, or a combination of these. An RNAV system may be included as part of a flight management system (FMS).
  2. RNP system. An area navigation system which supports on-board performance monitoring and alerting.
  3. Total System Error (TSE). The difference between true position and desired position. This error is equal to the vector sum of the path steering error, path definition error and position estimation error.

3.2.   Regulatory References

3.2.1.  The following reference materials should be used in conjunction with this document:

  1. ICAO Document 9613, Performance-based Navigation (PBN) Manual, Fourth Edition, 2012;
  2. Transport Canada Civil Aviation (TCCA), Canadian Aviation Regulation (CAR), Part VI – General Operating and Flight Rules, Subpart 4 – Private Operator Passenger Transportation;
  3. TCCA Canadian Aviation Regulation (CAR), Part V – Airworthiness Manual (AWM) 525.1309;
  4. TCCA Certification Memorandum, CM-FT-2 (RNP), 2010;
  5. Technical Airworthiness Manual (TAM), Change 6, dated June 2012;
  6. Operational Airworthiness Manual (OAM), Version 1.0, Change 5, dated November 2011;

3.2.2.  This TAA Advisory is mainly based on the regulatory framework established in Regulatory Reference 3.2.1.a.. In preparing this TAA Advisory, the TAA collated information from numerous sources. It is prudent that clearance of RNP on RCAF aircraft utilizes this information for guidance and applies it in the military context, where applicable.

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4.    Discussion

4.1.   Background

4.1.1.  In December 2005, the FAA published Advisory Circular (AC) 90-101 titled “Approval Guidance for RNP Procedures with SAAAR”. As the term “Special Aircraft and Aircrew Authorization Required” (SAAAR) implies, approvals to RNP procedures are for a specific operator, operating specified aircraft into specified airports. In January 2009, the FAA published AC 90-105, titled “Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System”, intended to address approach operations down to an RNP of 0.3 Nm. However, neither of these 90-Series ACs specifically addresses the aircraft certification requirements, so in September of 2010, the FAA published AC 20-138B, titled “Airworthiness Approval of Positioning and Navigation Systems”. FAA AC 20-138B states its intent is to capture the aircraft certification requirements from AC 90-101 and 90-105, for all RNP operations, and that 90-Series ACs will eventually be revised to remove the airworthiness guidance.

4.1.2.  More recently, in December 2009, EASA published Acceptable Means of Compliance (AMCs) 20-26 and 20-27 addressing, respectively, the Airworthiness approval of RNP Authorization Required (RNP AR) and RNP Approach (RNP APCH) operations. These are the first generic advisory circulars published by an airworthiness authority specifically addressing the airworthiness requirements for RNP. While the EASA AMCs are based on the criteria in the FAA ACs, they include more stringent criteria, notably in the area of aircraft performance in non-normal conditions.

4.1.3.  Both the FAA and EASA advisory material evolved from the ICAO Performance-Based Navigation (PBN) Manual, document 9613 published in 2008 (with the exception of AC 90-101, which pre-dated the PBN). The technical requirements in the PBN are internationally harmonized; however, the operational requirements that national authorities will implement, and the aircraft requirements for operations within that airspace, are still evolving. It is expected that, by reference to the EASA and FAA documents, compliance with this TAA Advisory will ensure that the RCAF meets all of the EASA and FAA airworthiness requirements that are currently anticipated.

4.1.4.  Approval for the RCAF aircraft for RNP operations may be separated into two phases, with the first phase addressing, as a minimum, Required Navigation Performance Approach (RNP APCH) operations down to 0.3 Nm (RNP APCH), and a follow-on approval phase or phases addressing additional RNP operations below 0.3 Nm (RNP AR).

4.2.   TAA Guidance

4.2.1.  In order to obtain an airworthiness approval for RNP APCH operations, the Applicant shall:

  1. follow the guidance of AMC 20-27;
  2. identify precisely the aircraft configuration(s) that is/are proposed for RNP APCH operations; and
  3. demonstrate that the installed system is compliant with chapters 6, 7, 8 and 9 of AMC 20-27.

4.2.2.  In order to obtain an airworthiness approval for RNP AR operations, the Applicant shall:

  1. follow the guidance of AMC 20-26;
  2. identify precisely the aircraft configuration(s) that is/are proposed for RNP AR operations;
  3. demonstrate that the installed system is compliant with chapters 6, 7, 8 and 9 of AMC 20-26; and
  4. any deviation or mitigation should be documented and will be addressed and evaluated by TAA Avionics and Flight Test specialists.

4.2.3.   In order to obtain an airworthiness approval for RNP-4 operations, the Applicant shall:

  1. follow the guidance of Appendix A of this TAA Advisory;
  2. identify precisely the aircraft configuration(s) that is/are proposed for RNP-4 operations; and
  3. any deviation or mitigation should be documented and will be addressed and evaluated by TAA Avionics and Flight Test specialists.

4.2.4.   In order to obtain an airworthiness approval for Basic RNP-1 operations, the Applicant shall:

  1. follow the guidance of Appendix B of this TAA Advisory;
  2. identify precisely the aircraft configuration(s) that is/are proposed for Basic RNP-1 operations; and
  3. any deviation or mitigation should be documented and will be addressed and evaluated by TAA Avionics and Flight Test specialists.

4.2.5.  In order to obtain an airworthiness approval for RNP-2 operations, the Applicant shall:

  1. follow the guidance for RNP-2 identified in ICAO PBN Manual, Part C, Chapter 2, section 2.3.3.;
  2. identify precisely the aircraft configuration(s) that is/are proposed for RNP-2 operations; and
  3. any deviation or mitigation should be documented and will be addressed and evaluated by TAA Avionics and Flight Test specialists.

4.3.     Certification Plan

4.3.1. The Applicant is requested to develop an RNP certification plan against the applicable portions of EASA AMC 20-26 and 20-27, and the additional aircraft requirements contained in this TAA Advisory. Such certification plan should define the RNP capabilities for which the Applicant is seeking TAA airworthiness certification.

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4.4.     Additional Considerations and Requirements

In addition, the Applicant is required to address the following:

4.4.1.    Performance Monitoring and Alerting Considerations

4.4.1.1. The performance monitoring and alerting function must be shown to perform its intended function and must not provide nuisance alerts.

4.4.1.2. Careful consideration is required to ensure a genuine alert is provided for RNP operations, while addressing transitions into and out of RNP airspace (e.g., RNP legs, or procedures such as RNP STARS and RNP approaches). Inserting non RNP HOLDS, DIRECT TO, and heading legs are all examples of transitioning in and out of RNP operations. When approaching RNP airspace from non-RNP airspace, alerting must be enabled when the cross-track deviation to the desired path is equal to or less than one-half the navigation accuracy and the aircraft has passed the first fix in the RNP airspace.

4.4.1.3. If it is possible for the pilot to manually enter RNP values, thereby overriding a default RNP value or an RNP value extracted from the database, then there must be an annunciation to alert the pilot if the entered value is larger than either the default value, or the RNP value associated with the current airspace. Any subsequent reduction of the RNP value associated with the airspace should reinstate this alerting function. Thus, if the aircraft transitions to airspace with a lower RNP value, e.g., from RNP-4 to RNP-1, and if the manually entered RNP value is still active, and higher than the RNP value for the newly entered airspace, then the alert of the manually entered RNP shall be re-enabled and annunciated.

4.4.1.4. If deviation indication is used, the full-scale deflection value must be appropriate for the RNP value and must be displayed to the pilot.

4.4.1.5. If a map display is to be considered as acceptable for monitoring FTE, the map scale must be appropriate for the RNP value and the map must be continuously displayed to the pilot. It must also be shown that the required continuous display of the map does not adversely affect the functionality of other systems (such as the operational use of weather radar, Airborne Collision Avoidance System (ACAS) and Terrain Awareness Warning System (TAWS) by either/both pilots that may require the use of an inappropriate scale).

NOTE

An automatic monitoring of the FTE is not required. The on-board monitoring and alerting function should consist at least of a Navigation System Error (NSE) monitoring and alerting algorithm and a lateral navigation display indicator enabling the crew to monitor the FTE.

4.4.2.    FTE Bounding Requirements

4.4.2.1. The FTE Bounding Requirements of AMC 20-27 are applicable to RNP APCH. For Basic RNP-1, RNP-2 (if applicable) and RNP-4, the FTE needs to be bound to 1 x RNP, 95% of the time, for all approved operating modes (e.g., autopilot (AP) on/off, Flight Director (FD) on/off).

4.4.3.   Pilot Workload to Maintain FTE for Manual Flight

4.4.3.1.  If manually flown (i.e., AP Off) RNP procedures are permitted, either with FD on or off, the pilot workload required to maintain FTE within the applicable bounds in operationally representative scenarios must be addressed. Specific RNP crew operating procedures may be required. If applicable, realistic time limitations should be established for each RNP approval sought. (For example, it may not be realistic to assume that a pilot can maintain 95% FTE on an RNP 1 enroute segment for more than two (2) hours. Similarly, it may not even be possible for manually flown procedures to maintain the FTE required for RNP of less than 0.3 Nm). Such limitations may be a function of time, RNP value and aircraft configuration (displays, handling qualities, etc.). If workload is determined to be limiting, then time limits may need to be reflected in the AFM. If not limiting, recommendations to support operational approvals should be contained in the Operational Support Document.

4.4.4.    Alerting

4.4.4.1.  The RNP system shall provide a visible alert within the flight crew’s primary field of view when loss of navigation capability and/or loss of integrity are experienced.

4.4.5.    Functional Requirements

4.4.5.1.  An AP or FD with at least “roll-steering” capability that is driven by the RNP system is required. The autopilot/flight director must operate with suitable accuracy to track the lateral and, as appropriate vertical paths required by a specific RNP procedure.

4.4.5.2.  The aircraft must have an electronic map display depicting the RNP computed path of the selected procedure.

4.4.5.3.  All AP modes, FD modes and Flying Model Simulator (FMS) functions, intended to be approved with radio frequency (RF) functionality must be capable of commanding up to 25 degrees bank angle, above 400 feet above ground level (AGL), without limit. Any function that limits the maximum bank angle to less than this must be made incompatible with the activation of a curved path leg.

4.4.5.4.  The flight guidance mode should remain in lateral navigation (LNAV) while on an RF leg, when a procedure is abandoned or a missed approach/go-around is initiated (through activation of Take Off, Go Around (TOGA) or other means) to enable display of deviation and display of positive course guidance during the RF leg.

4.4.5.5.  The accuracy, integrity, continuity, and performance monitoring and Alerting Requirements of the corresponding capability (e.g., RNP Authorization Required (AR), RNP Approach (APCH), Basic RNP-1) to which the RF function is attached, are applicable.

4.4.5.6.  RNP significant failure modes must be addressed for the RF leg function.

4.4.6.  RNP Significant Failure Modes

4.4.6.1.  The Applicant shall review any new and existing aircraft failure modes that potentially affect RNP capability. Probable and improbable failures (as defined by Regulatory Reference 3.2.1.c.) need to be reviewed in the context of their impact on the RNP capability to be approved. Where appropriate, mitigating flight crew procedures for RNP operations will need to be developed.

4.4.6.2.  Failures that need to be reviewed include, but are not limited to:

  1. Failures that significantly disturb the aircraft laterally,
  2. Failures that result in degraded navigation capability,
  3. Failures that affect the performance monitoring and alerting,
  4. Failures that impact the crew’s ability to focus on the navigation task during RNP operations.

4.4.6.3.  For RNP significant probable failures, the aircraft must demonstrate the ability to remain within 1 x RNP Total System Error (TSE) using any applicable crew operating procedures.

4.4.6.4.  In addition, for RNP AR, for RNP significant improbable failures, the aircraft must demonstrate the ability to remain within 2 x RNP TSE using any applicable crew operating procedures.

4.4.6.5.  The demonstration of failure effects and validation of associated RNP AFM procedures may require an appropriate simulator and/or a representative aircraft.

NOTE

Typical failures that may have RNP significant effects include loss of electrical power, navigation sensor failures, engine failure, and failures of performance monitoring and alerting functionality.

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4.4.7.  Functional Hazard Assessment Requirements.

4.4.7.1.  The following classifications shall be used for the functional hazard assessment.

 

 

RNP                   

APCH                 

RNP AR

≥ 0.3 Nm for Approach, and

≥ 1.0 Nm for Missed Approach

RNP AR

< 0.3 Nm for Approach, or

< 1.0 Nm for Missed Approach

Display of misleading lateral or vertical guidance

Major

Major

Hazardous

Loss of lateral RNP guidance

Minor1

Major2
Minor3

Hazardous

 


  1. Loss of lateral RNP guidance during RNP APCH is Minor if the following assumptions remain valid:
    1. Aircraft executes a missed approach upon loss of lateral RNP guidance; and
    2. The aircraft maintains some means of navigation, e.g., VHF omnidirectional range/Distance measuring equipment (VOR/DME), regardless of whether that means of navigation allows for continued RNAV operations.
  2. Loss of lateral RNP guidance during RNP AR (≥ 0.3 Nm Approach / ≥ 1.0 Nm Missed Approach) is Major if aircraft does not maintain a means of navigation that allows for continued RNAV operations. 
  3. Loss of lateral RNP guidance during RNP AR (≥ 0.3 Nm Approach / ≥ 1.0 Nm Missed Approach) is Minor if the following assumptions remain valid:
    1. Aircraft initiates a climb and follows the missed approach procedure upon loss of lateral RNP guidance; and
    2. The aircraft maintains a means of navigation that allows for continued RNAV operations that allows it to fly the published missed approach procedure. 

4.4.8.  Database Assurance

4.4.8.1.  The aircraft’s navigation database must be obtained from a supplier that complies with RTCA DO 200A/EUROCAE document ED 76, Standards for Processing Aeronautical Data, and should be compatible with the intended function of the equipment. The Applicant must establish and ensure that a process exists to identify and communicate database errors, and to communicate their resolution of those errors to all database users and supplier(s).

4.4.9.  Aircraft Flight Manual (AFM)

4.4.9.1.  The AFM must contain at least the following information:

  1. Statements indicating which RNP capabilities the aircraft meets (e.g., RNP AR, RNP APCH, Basic RNP-1);
  2. Any limitations associated with each of the RNP capabilities. These should address mode of flight (e.g., FD on or off; and/or AP on or off, and applicable lateral and vertical modes), and/or Course Deviation Indicator (CDI)/map scaling requirements, and sensor limitations, if any;
  3. A statement indicating the aircraft meets the requirements for RNP operations with RF legs;
  4. Any specific operating procedures applicable to the installed equipment and required to support the RNP approval (e.g., Emergency, Abnormal, Normal procedures); and
  5. The minimum aircraft configuration required for each type of RNP operation. This may include equipment such as navigation equipment, displays, Automatic Flight Control System (AFCS), air data, TAWS, etc., and their associated software versions, if applicable.

4.4.10. Pilot Procedures

4.4.10.1. The pilot procedures that are RNP specific (e.g., flight crew operational bounding of FTE, response to NSE alert, use of performance monitoring and alerting functions, crew action for failures), and necessary to achieve the desired RNP performance, shall be addressed in the Flight Crew Operating Manual (FCOM), or similar document, and shall be made available to the TAA for their certification evaluation. The operating procedures section should expand on and complement AFM procedures.

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4.5.  RNP Operational Support Document

4.5.1.   It is recommended that the Applicant develop an RNP Operational Support Document in parallel with the certification process. The purpose of this document is to facilitate operational approval of the aircraft for RNP operations anywhere in the world that are based on the ICAO PBN Navigation Specifications. Since communication and surveillance are integral parts of an airspace concept, the document should also reflect these aircraft capabilities to facilitate operational approvals.

4.5.2.   If the Applicant wishes to reference the RNP capabilities document in the AFM General section, then it must be provided to the TAA for review.

4.5.3.   The RNP Operational Support document should include, but not be limited to, the following:

  1. A description of the aircraft configuration and systems required to support RNP operation;
  2. A description of the interface between the navigation function and the flight crew;
  3. A description of the specific navigation capabilities of the system;
  4. Guidelines for Minimum Equipment List (MEL) considerations;
  5. Flight crew workload guidelines for limiting the time allowed for manual flight RNP operations;
  6. A description of all the assumptions on systems and considerations external to the aircraft (e.g., signal in space performance, coverage, survey accuracy, procedure design and obstacle clearance, climb gradients, wind limitations, temperature limitations, etc.);
  7. A description of the use of performance monitoring and alerting functionality in non RNP airspace with the intent of providing meaningful guidelines for operationally relevant use of such functionality (i.e., optional use of this functionality on VOR or RNAV routes);
  8. A description of the Communications capabilities of the RNP configured aircraft (VHF, UHF, SATCOM, CPDLC Datalink, etc.); and
  9. A description of the aircraft capabilities to support surveillance (ADS-B, ADS-C, Mode S, etc.).

4.5.4.   Compliance with this TAA Advisory will allow the Applicant to include wording in the AFM explicitly stating that the aircraft meets the requirements of:

  1. Chapters 6, 7, 8 and 9 of EASA AMC 20-26;
  2. Chapters 6, 7, 8 and 9 of EASA AMC 20-27; and
  3. Subject to the limitations specified in the AFM.

4.5.5.   Compliance with this TAA Advisory will allow the Applicant to include wording in the AFM explicitly stating that the aircraft supports operational approvals for:

  1. RNP-4 Operations per ICAO PBN Volume II, Part C, Chapter 1;
  2. Basic RNP-2 Operations per ICAO PBN Volume, Part C, Chapter 2;
  3. Basic RNP-1 Operations per ICAO PBN Volume II, Part C, Chapter 3;
  4. Basic RNP-APCH Operations per ICAO PBN Volume II, Part C, Chapter 5;
  5. Basic RNP-AR Operations per ICAO PBN Volume II, Part C, Chapter 6; and
  6. Subject to the limitations specified in the AFM.

4.5.6.   Compliance with this TAA Advisory and the above criteria will allow the Applicant to include wording in the AFM explicitly stating that the aircraft complies with the appropriate provisions of FAA document AC 90-105 for:

  1. FAA RNP instrument approach operations;
  2. FAA RNP 1 (Terminal) operations;
  3. FAA Baro VNAV approach operations in accordance with AC 20-138C;
  4. FAA RNP operations with RF legs; and
  5. Subject to the limitations specified in the AFM.

4.5.7.   Compliance with this TAA Advisory and the above criteria will allow the Applicant to include wording in the AFM explicitly stating that the aircraft complies with the appropriate provisions of AC 90-101 for:

  1. FAA RNP SAAAR operations; and,
  2. Subject to the limitations specified in the AFM.

4.5.8.   Compliance with this TAA Advisory and the above criteria will allow the Applicant to include wording in the AFM explicitly stating that the aircraft complies with the appropriate provisions of FAA Order 8400.33 for RNP-4 operations.

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