RNAV: Random or Area Navigation Explained

RNAV, which stands for Random Navigation or Area Navigation, is an avionic system that uses short-range navigational aids. It provides an aircraft’s bearing and distance with reference to a 3D artificial reference point, known as a Waypoint (WPT). The main goal of using computerized WPTs is to create optimized air routes from departure to arrival.

To define WPTs, the system needs the aircraft’s present 3D position fix. This can be obtained in three ways:

1. Ground Stations: Using VOR-DME or VORTAC to get bearing and distance. These measurements are then converted to Aircraft latitude and longitude. A radio altimeter in the aircraft radar provides the altitude.
2. Self-Contained Systems: Using systems like INS (Inertial Navigation System) and DNS (Doppler Navigation System).
3. Orbital Satellite Systems: Utilizing systems such as GPS (Global Positioning System).

Within the aircraft, the RNAV system performs the following tasks:

• RNAV calculates WPTs or uses pre-loaded WPTs from a NAV Database based on the aircraft’s current position and the flight plan to reach the destination.
• Once a WPT is identified in 3D space, the aircraft’s bearing and distance to that WPT are determined, allowing the aircraft to fly toward it.

Some RNAV systems also provide these additional parameters:

• Estimated Time of Arrival (ETA) to the next WPT.
• Necessary Indicated Airspeed (IAS) required to achieve the ETA.
• Fuel consumption.

INS, DNS, or GPS facilitate the use of RNAV in oceanic airspace where ground stations are unavailable.

Advantages of RNAV

• RNAV enables more direct, efficient, and flexible routes.
• Faster arrival times at the destination.
• Cost-effective navigation.
• Increased air traffic capacity at random locations, reducing congestion in specific geographical areas.
• Improved utilization of airspace.

Disadvantages of RNAV

• Susceptible to the same errors as VOR, DME, and VORTAC systems.
• The possibility of obtaining fictitious WPTs through corresponding ground stations is limited by the operational range.
• RNAV airways are narrower than traditional V and J airways. RNAV airway width is approximately 8 nautical miles (15 km), while V or J airways are about 10 nautical miles (16 km) wide.