Area Navigation Systems (RNAV) — Page 262, Lesson 257

Let's start with the definition, because everything else hangs off it. RNAV, Area Navigation, is defined as a method of navigation which permits aircraft operations on any desired track within the coverage of station-referenced navigation signals, or within the limits of a self-contained navigation system. Let me unpack that. Traditionally, you fly from one ground beacon to the next, tracking directly over each one. RNAV frees you from that. "Any desired track" means you can fly a straight line between any two points you choose, as long as you're within the coverage of the ground-based signals you're using, or within the limits of your own self-contained system. So an area navigation system is any system that lets you navigate to the required level of accuracy without having to fly directly over ground-based facilities. Now, where does that accuracy come from? The system uses some, or all, of the following inputs: VOR/DME, ILS/MLS, GNSS, INS/IRS, ADC, and Time. Let me name each one properly. VOR is VHF Omni-directional Range, DME is Distance Measuring Equipment. ILS is the Instrument Landing System, MLS is the Microwave Landing System. GNSS is the Global Navigation Satellite System. INS is Inertial Navigation System, IRS is Inertial Reference System. ADC is the Air Data Computer. And time is simply time. The system processes all these inputs to give you the most accurate, continuously updated position, and then produces the outputs you need — course, ETA, and so on. Why bother? The benefits. RNAV lets the aircraft take a more direct flight path, which improves operating efficiency and relieves congestion on the overcrowded airway system. Air traffic control centres have established RNAV routes that are more direct than the traditional airways, and they don't require you to regularly fly overhead of beacons. So the benefits are: a reduction in distance, flight time and fuel — and hence costs — by giving airlines and pilots greater flexibility and choice of routes. An increase in route capacity by making full use of available airspace, providing more direct routes, parallel or dual routes, and bypass routes for overflying aircraft in high-density terminal areas. And a reduction in vertical and horizontal separation criteria. Now the types and levels. There are two types of RNAV. Basic RNAV, B-RNAV, which must give a position accuracy to within 5 nautical miles on at least 95% of occasions. It's now mandatory for all aircraft carrying 30 passengers or more to have B-RNAV capability within Eurocontrol airspace. Then Precision RNAV, P-RNAV, which must be accurate to within 1.0 nautical mile on at least 95% of occasions. P-RNAV routes are now being established in terminal airspace. There are also three levels of RNAV capability. 2D RNAV relates to capabilities in the horizontal plane only. 3D RNAV adds a guidance capability in the vertical plane. And 4D RNAV adds to 3D a timing function. Let me show you the flight deck of a simple 2D RNAV system. It includes the Navigation Computer Unit, the Control and Display Unit — the CDU — and an indicator, which is either a Course Deviation Indicator, the CDI, or a Horizontal Situation Indicator, the HSI. The Navigation Computer Unit is the brain, processing the inputs. The CDU is your interface, where you enter and read data. And the CDI or HSI is the display that shows you the deviation from your chosen track. That figure shows the VOR/DME RNAV integrated navigation system — the physical layout of these components in the cockpit. So that's the foundation: the definition, the inputs, the benefits, the two types with their accuracy requirements, the three levels of capability, and the components of a simple 2D system.