Area Navigation (R-Nav)

Wing Commander Rajagopal

Area Navigation System (RNAV)

Area Navigation (RNAV) is a navigation method that allows aircraft to fly on any desired flight path within the coverage of navigation aids or using onboard navigation systems. It uses systems such as GNSS, DME/DME, and INS/IRS to determine the aircraft’s position accurately. RNAV improves route efficiency, reduces flight time and fuel consumption, and enhances airspace capacity.

Area Navigation System (RNAV)

  • Area Navigation (RNAV) is a navigation system that allows an aircraft to fly on any desired flight path.
  • The flight path may be referenced to ground-based navigation aids such as VOR/DME.
  • It may also be referenced to self-contained navigation systems such as INS or IRS.
  • RNAV can combine information from both ground-based and self-contained navigation aids.
  • RNAV enables aircraft to fly directly between waypoints without passing overhead ground navigation facilities.

Required Navigation Performance (RNP)

  • Required Navigation Performance (RNP) defines the navigation accuracy required when operating on RNAV routes.
  • Accuracy is specified at a 95% probability level.
  • The requirement applies in both the lateral and longitudinal directions.
  • Example: RNP 5 means:
    • 95% of aircraft operating on the route remain within 5 NM of their intended position.
    • An aircraft will remain within 5 NM of its calculated position for 95% of the flight time.

Mandatory Accuracy for Required Navigation Performance

  • RNP requirements may be specified for:
    • A single route.
    • A group of routes.
    • A defined area.
    • A specified volume of airspace.
  • RNAV systems determine aircraft position using information from:
    • VOR
    • DME
    • GPS
    • ILS
    • MLS
    • INS
    • IRS
    • Air Data Computer (ADC)
    • Time information
  • The system processes these inputs to calculate:
    • Track Made Good (TMG).
    • Estimated Time of Arrival (ETA).

Air Traffic Management using Area Navigation Systems

Advantages of RNAV Routes

Operational Advantages

  • Aircraft can fly direct routes over the shortest distance.
  • Reduced flight time.
  • Lower fuel consumption.
  • Reduced operating costs.

Air Traffic Control Advantages

  • Increased route capacity.
  • Additional route options.
  • Reduced horizontal and vertical separation requirements where approved.
  • Greater flexibility in traffic management.
  • Provision of:
    • ATC-designed RNAV routes.
    • Bypass routes.
    • Contingency routes.
    • Optimum holding patterns and locations.
  • Reduced dependence on ground-based navigation facilities.

2D, 3D and 4D Area Navigation Systems

Types of RNAV Systems

  • Basic RNAV provides navigation accuracy of 5 NM (95% probability).
  • Precision RNAV (P-RNAV) provides navigation accuracy of 1 NM (95% probability).

Levels of RNAV Guidance

  • 2D RNAV – Horizontal guidance only.
  • 3D RNAV – Horizontal and vertical guidance.
  • 4D RNAV – Horizontal, vertical and time-based navigation.

RNAV Control Unit

Waypoint Inputs

  • Waypoint number.
  • Navigation beacon frequency.
  • Bearing and distance from the reference beacon.

RNAV Display

  • RNAV guidance is displayed on the Horizontal Situation Indicator (HSI).
  • Full-scale HSI deflection represents:
    • 5 NM deviation during the en-route phase.
    • 1.5 NM deviation during the approach phase.
    • 10° deviation while tracking inbound or outbound using VOR/DME.

RNAV Routes Based on Phantom Stations

  • RNAV routes are constructed using Phantom Stations.
  • Phantom Stations are computer-generated RNAV waypoints.
  • These waypoints are defined by their bearing and distance from existing VOR/DME stations.

Limitations of 2D RNAV System

  • 2D RNAV depends upon VOR/DME signals being within line of sight.
  • Mountainous terrain may block navigation signals.
  • The aircraft must remain within the Designated Operational Coverage (DOC) of the VOR/DME.
  • Outside the DOC, navigation inputs may become inaccurate.
  • DME measures slant range, which can introduce errors when flying close to the station.

4D RNAV Operation

  • 4D RNAV receives inputs from:
    • INS
    • IRS
    • GPS
    • VOR/DME
  • The Flight Management Computer (FMC) compares all available navigation sources to determine the most accurate aircraft position.
  • The FMC automatically selects the best navigation solution.

Navigation Priority

  1. DME/DME Fix – Preferred due to highest accuracy.
  2. VOR/DME Fix – Second preference because VOR accuracy is limited to approximately ±5°.
  3. VOR/VOR Fix – Third preference because accuracy decreases significantly with distance (approximately 35 NM).

Advanced Dead Reckoning by the Flight Management Computer (FMC)

  • 4D RNAV performs an advanced form of Dead Reckoning (DR).
  • The FMC receives:
    • True Airspeed (TAS) from the Air Data Computer (ADC).
    • Heading from the Remote Indicating Compass (RIC) or heading reference system.
  • The FMC calculates the actual wind velocity using these inputs.
  • If the aircraft is outside VOR/DME coverage, the FMC uses IRS or INS for navigation.
  • Dead Reckoning calculations are based on:
    • Last known position.
    • Aircraft heading.
    • True Airspeed (TAS).
  • The FMC computes steering commands to fly the most efficient Great Circle Route.