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Area Navigation

Introduction:

  • As air travel has evolved, methods of navigation have improved to give operators more flexibility
  • Under the umbrella of area navigation, there are legacy and performance−based navigation (PBN) methods [Figure 1]
  • Legacy Methods:

    • The legacy methods include operations incorporating systems approved under AC 90-45, Approval of Area Navigation Systems for Use in the U.S. National Airspace System, which allows two-dimensional area navigation (2D RNAV) within the U.S. National Airspace System (NAS)
    • AC 90-45 describes 2D RNAV in terms of both VOR/DME dependent systems and self-contained systems such as Inertial Navigation Systems (INS)
  • Performance-Based Navigation:

    • Many operators have upgraded their systems to obtain the benefits of PBN
    • Within PBN there are two main categories of navigation methods:
      • Area navigation (RNAV):

        • For an aircraft to meet the requirements of RNAV, a specified RNAV accuracy must be met 95 percent of the flight time
      • Required navigation performance (RNP):

        • RNP is an RNAV system that includes onboard performance monitoring and alerting capability (for example, Receiver Autonomous Integrity Monitoring (RAIM))
    • PBN also introduces the concept of navigation specifications (Nav Specs) which are a set of aircraft and aircrew requirements needed to support a navigation application within a defined airspace concept. For both RNP and RNAV designations, the numerical designation refers to the lateral navigation accuracy in nautical miles which is expected to be achieved at least 95 percent of the flight time by the population of aircraft operating within the airspace, route, or procedure. This information is introduced in International Civil Aviation Organization’s (ICAO) Doc 9613, Performance-based Navigation (PBN) Manual (Fourth Edition, 2013) and the FAA Advisory Circular (AC) 90-105A, Approval Guidance for RNP Operations and Barometric Vertical Navigation in the U.S. National Airspace System and in Remote and Oceanic Airspace (expected publication date in late 2014) further develops this story

Area Navigation (RNAV):

  • RNAV is a method of navigation that permits aircraft operation on any desired flight path within the coverage of ground− or space−based navigation aids or within the limits of the capability of self−contained aids, or a combination of these. In the future, there will be an increased dependence on the use of RNAV in lieu of routes defined by ground−based navigation aids. RNAV routes and terminal procedures, including departure procedures (DPs) and standard terminal arrivals (STARs), are designed with RNAV systems in mind. There are several potential advantages of RNAV routes and procedures:
    • Time and fuel savings
    • Reduced dependence on radar vectoring, altitude, and speed assignments allowing a reduction in required ATC radio transmissions, and
    • More efficient use of airspace
  • In addition to information found in this manual, guidance for domestic RNAV DPs, STARs, and routes may also be found in Advisory Circular 90−100(), U.S. Terminal and En Route Area Navigation (RNAV) Operations
  • RNAV Operations:

    • RNAV procedures, such as DPs and STARs, demand strict pilot awareness and maintenance of the procedure centerline. Pilots should possess a working knowledge of their aircraft navigation system to ensure RNAV procedures are flown in an appropriate manner. In addition, pilots should have an understanding of the various waypoint and leg types used in RNAV procedures; these are discussed in more detail below
      • Waypoints:

        • A waypoint is a predetermined geographical position that is defined in terms of latitude/longitude coordinates. Waypoints may be a simple named point in space or associated with existing navaids, intersections, or fixes. A waypoint is most often used to indicate a change in direction, speed, or altitude along the desired path. RNAV procedures make use of both fly−over and fly−by waypoints [Figure 2]
        • Fly−by waypoints:
          • Fly−by waypoints are used when an aircraft should begin a turn to the next course prior to reaching the waypoint separating the two route segments. This is known as turn anticipation
        • Fly−over waypoints:
          • Fly−over waypoints are used when the aircraft must fly over the point prior to starting a turn
      • RNAV Leg Types:

        • A leg type describes the desired path proceeding, following, or between waypoints on an RNAV procedure. Leg types are identified by a two−letter code that describes the path (e.g., heading, course, track, etc.) and the termination point (e.g., the path terminates at an altitude, distance, fix, etc.). Leg types used for procedure design are included in the aircraft navigation database, but not normally provided on the procedure chart. The narrative depiction of the RNAV chart describes how a procedure is flown. The “path and terminator concept” defines that every leg of a procedure has a termination point and some kind of path into that termination point. Some of the available leg types are described below
        • Track to Fix:
          • A Track to Fix (TF) leg is intercepted and acquired as the flight track to the following waypoint. Track to a Fix legs are sometimes called point−to−point legs for this reason. Narrative: “direct ALPHA, then on course to BRAVO WP.” [Figure 3]
        • Direct to Fix:
          • A Direct to Fix (DF) leg is a path described by an aircraft’s track from an initial area direct to the next waypoint. Narrative: “turn right direct BRAVO WP.” [Figure 4]
        • Course to Fix:
          • A Course to Fix (CF) leg is a path that terminates at a fix with a specified course at that fix. Narrative: “on course 150 to ALPHA WP.” [Figure 5]
        • Radius to Fix:
          • A Radius to Fix (RF) leg is defined as a constant radius circular path around a defined turn center that terminates at a fix. [Figure 6]
        • Heading:
          • A Heading leg may be defined as, but not limited to, a Heading to Altitude (VA), Heading to DME range (VD), and Heading to Manual Termination, i.e., Vector (VM). Narrative: “climb heading 350 to 1500”, “heading 265, at 9 DME west of PXR VORTAC, right turn heading 360”, “fly heading 090, expect radar vectors to DRYHT INT"
      • Navigation Issues:

        • Pilots should be aware of their navigation system inputs, alerts, and annunciations in order to make better−informed decisions. In addition, the availability and suitability of particular sensors/systems should be considered
        • GPS/WAAS:
          • Operators using TSO−C129(), TSO−C196(), TSO−C145() or TSO−C146() systems should ensure departure and arrival airports are entered to ensure proper RAIM availability and CDI sensitivity
        • DME/DME:
          • Operators should be aware that DME/DME position updating is dependent on navigation system logic and DME facility proximity, availability, geometry, and signal masking
        • VOR/DME:
          • Unique VOR characteristics may result in less accurate values from VOR/DME position updating than from GPS or DME/DME position updating
        • Inertial Navigation
          • Inertial reference units and inertial navigation systems are often coupled with other types of navigation inputs, e.g., DME/DME or GPS, to improve overall navigation system performance
          • NOTE−Specific inertial position updating requirements may apply
      • Flight Management System (FMS):

        • An FMS is an integrated suite of sensors, receivers, and computers, coupled with a navigation database. These systems generally provide performance and RNAV guidance to displays and automatic flight control systems
        • Inputs can be accepted from multiple sources such as GPS, DME, VOR, LOC and IRU. These inputs may be applied to a navigation solution one at a time or in combination. Some FMSs provide for the detection and isolation of faulty navigation information
        • When appropriate navigation signals are available, FMSs will normally rely on GPS and/or DME/DME (that is, the use of distance information from two or more DME stations) for position updates. Other inputs may also be incorporated based on FMS system architecture and navigation source geometry
        • NOTE−DME/DME inputs coupled with one or more IRU(s) are often abbreviated as DME/DME/IRU or D/D/I
      • RNAV Navigation Specifications (Nav Specs):

        • Nav Specs are a set of aircraft and aircrew requirements needed to support a navigation application within a defined airspace concept. For both RNP and RNAV designations, the numerical designation refers to the lateral navigation accuracy in nautical miles which is expected to be achieved at least 95 percent of the flight time by the population of aircraft operating within the airspace, route, or procedure. [Figure 1]
        • RNAV 1:
          • Typically RNAV 1 is used for DPs and STARs and appears on the charts. Aircraft must maintain a total system error of not more than 1 NM for 95 percent of the total flight time
        • RNAV 2:
          • Typically RNAV 2 is used for en route operations unless otherwise specified
          • T-routes and Q-routes are examples of this Nav Spec
          • Aircraft must maintain a total system error of not more than 2 NM for 95 percent of the total flight time
        • RNAV 10:
          • Typically RNAV 10 is used in oceanic operations. See paragraph 4−7−1 for specifics and explanation of the relationship between RNP 10 and RNAV 10 terminology

Use of Suitable Area Navigation (RNAV) Systems on Conventional Procedures and Routes:

  • This paragraph sets forth policy, while providing operational and airworthiness guidance regarding the suitability and use of RNAV systems when operating on, or transitioning to, conventional, non−RNAV routes and procedures within the U.S. National Airspace System (NAS):
    • Use of a suitable RNAV system as a Substitute Means of Navigation when a Very−High Frequency (VHF) Omni−directional Range (VOR), Distance Measuring Equipment (DME), Tactical Air Navigation (TACAN), VOR/TACAN (VORTAC), VOR/DME, Non−directional Beacon (NDB), or compass locator facility including locator outer marker and locator middle marker is out−of−service (that is, the navigation aid (NAVAID) information is not available); an aircraft is not equipped with an Automatic Direction Finder (ADF) or DME; or the installed ADF or DME on an aircraft is not operational. For example, if equipped with a suitable RNAV system, a pilot may hold over an out−of−service NDB
    • Use of a suitable RNAV system as an Alternate Means of Navigation when a VOR, DME, VORTAC, VOR/DME, TACAN, NDB, or compass locator facility including locator outer marker and locator middle marker is operational and the respective aircraft is equipped with operational navigation equipment that is compatible with conventional navaids. For example, if equipped with a suitable RNAV system, a pilot may fly a procedure or route based on operational VOR using that RNAV system without monitoring the VOR.
      • NOTE 1: Additional information and associated requirements are available in Advisory Circular 90-108 titled “Use of Suitable RNAV Systems on Conventional Routes and Procedures.”
      • NOTE 2: Good planning and knowledge of your RNAV system are critical for safe and successful operations
      • NOTE 3: Pilots planning to use their RNAV system as a substitute means of navigation guidance in lieu of an out−of−service NAVAID may need to advise ATC of this intent and capability
      • NOTE 4: The navigation database should be current for the duration of the flight. If the AIRAC cycle will change during flight, operators and pilots should establish procedures to ensure the accuracy of navigation data, including suitability of navigation facilities used to define the routes and procedures for flight. To facilitate validating database currency, the FAA has developed procedures for publishing the amendment date that instrument approach procedures were last revised. The amendment date follows the amendment number, e.g., Amdt 4 14Jan10. Currency of graphic departure procedures and STARs may be ascertained by the numerical designation in the procedure title. If an amended chart is published for the procedure, or the procedure amendment date shown on the chart is on or after the expiration date of the database, the operator must not use the database to conduct the operation
  • Types of RNAV Systems that Qualify as a Suitable RNAV System:

    • When installed in accordance with appropriate airworthiness installation requirements and operated in accordance with applicable operational guidance (e.g., aircraft flight manual and Advisory Circular material), the following systems qualify as a suitable RNAV system:
      • An RNAV system with TSO−C129/−C145/−C146 equipment, installed in accordance with AC 20−138, Airworthiness Approval of Global Positioning System (GPS) Navigation Equipment for Use as a VFR and IFR Supplemental Navigation System, or AC 20−130A, Airworthiness Approval of Navigation or Flight Management Systems Integrating Multiple Navigation Sensors, and authorized for instrument flight rules (IFR) en route and terminal operations (including those systems previously qualified for “GPS in lieu of ADF or DME” operations), or
      • An RNAV system with DME/DME/IRU inputs that is compliant with the equipment provisions of AC 90−100A, U.S. Terminal and En Route Area Navigation (RNAV) Operations, for RNAV routes. A table of compliant equipment is available at the following website: http://www.faa.gov/about/office_org/headquarters_offices/avs/offices/afs/
        • NOTE:
          Approved RNAV systems using DME/DME/IRU, without GPS/WAAS position input, may only be used as a substitute means of navigation when specifically authorized by a Notice to Airmen (NOTAM) or other FAA guidance for a specific procedure. The NOTAM or other FAA guidance authorizing the use of DME/DME/IRU systems will also identify any required DME facilities based on an FAA assessment of the DME navigation infrastructure
  • Uses of Suitable RNAV Systems:

    • Subject to the operating requirements, operators may use a suitable RNAV system in the following ways
      • Determine aircraft position relative to, or distance from a VOR (see NOTE 6 below), TACAN, NDB, compass locator, DME fix; or a named fix defined by a VOR radial, TACAN course, NDB bearing, or compass locator bearing intersecting a VOR or localizer course
      • Navigate to or from a VOR, TACAN, NDB, or compass locator
      • Hold over a VOR, TACAN, NDB, compass locator, or DME fix
      • Fly an arc based upon DME
    • NOTE 1: The allowances described in this section apply even when a facility is identified as required on a procedure (for example, "Note ADF required")
    • Note 2: These operations do not include lateral navigation on localizer-based courses (including localizer back-course guidance) without reference to raw localizer data
    • Note 3: Unless otherwise specified, a suitable RNAV system cannot be used for navigation on procedures that are identified as not authorized (“NA”) without exception by a NOTAM. For example, an operator may not use a RNAV system to navigate on a procedure affected by an expired or unsatisfactory flight inspection, or a procedure that is based upon a recently decommissioned NAVAID
    • Note 4: Pilots may not substitute for the NAVAID (for example, a VOR or NDB) providing lateral guidance for the final approach segment. This restriction does not refer to instrument approach procedures with “or GPS” in the title when using GPS or WAAS. These allowances do not apply to procedures that are identified as not authorized (NA) without exception by a NOTAM, as other conditions may still exist and result in a procedure not being available. For example, these allowances do not apply to a procedure associated with an expired or unsatisfactory flight inspection, or is based upon a recently decommissioned NAVAID
    • Note 5: Use of a suitable RNAV system as a means to navigate on the final approach segment of an instrument approach procedure based on a VOR, TACAN or NDB signal, is allowable. The underlying NAVAID must be operational and the NAVAID monitored for final segment course alignment
    • Note 6: For the purpose of this section, "VOR" includes VOR, VOR/DME, and VORTAC facilities and “compass locator” includes locator outer marker and locator middle marker
  • Alternate Airport Considerations:

    • For the purposes of flight planning, any required alternate airport must have an available instrument approach procedure that does not require the use of GPS. This restriction includes conducting a conventional approach at the alternate airport using a substitute means of navigation that is based upon the use of GPS. For example, these restrictions would apply when planning to use GPS equipment as a substitute means of navigation for an out−of−service VOR that supports an ILS missed approach procedure at an alternate airport. In this case, some other approach not reliant upon the use of GPS must be available. This restriction does not apply to RNAV systems using TSO−C145/−C146 WAAS equipment. For further WAAS guidance, see paragraph 1−1−18
      • For flight planning purposes, TSO-C129() and TSO-C196() equipped users (GPS users) whose navigation systems have fault detection and exclusion (FDE) capability, who perform a preflight RAIM prediction at the airport where the RNAV (GPS) approach will be flown, and have proper knowledge and any required training and/or approval to conduct a GPS-based IAP, may file based on a GPS-based IAP at either the destination or the alternate airport, but not at both locations. At the alternate airport, pilots may plan for applicable alternate airport weather minimums using:
        • Lateral navigation (LNAV) or circling minimum descent altitude (MDA);
        • LNAV/vertical navigation (LNAV/VNAV) DA, if equipped with and using approved barometric vertical navigation (baro­VNAV) equipment;
        • RNP 0.3 DA on an RNAV (RNP) IAP, if they are specifically authorized users using approved baro­VNAV equipment and the pilot has verified required navigation performance (RNP) availability through an approved prediction program
      • If the above conditions cannot be met, any required alternate airport must have an approved instrument approach procedure other than GPS that is anticipated to be operational and available at the estimated time of arrival, and which the aircraft is equipped to fly
      • This restriction does not apply to TSO­C145() and TSO­C146() equipped users (WAAS users). For further WAAS guidance see AIM 1-1-18

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