Area Navigation

• 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

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

    • Fly-by waypoints: [Figure 1]

      • 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: [Figure 1]

      • 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

    • 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 that 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 that 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 AIM paragraph 4-7-1 for specifics and explanation of the relationship between RNP 10 and RNAV 10 terminology