Both types of PNB are rated based on how accurately they fix the aircraft’s position. The two categories of PNB are RNAV and RNP (required navigation performance) systems. Performance-based navigation (PNB) is the classification of how well a navigation system performs. This is especially important for IFR operations. Since different technologies have different accuracy levels, some standardization has been introduced to clarify what RNAV technologies can be used when. Today, the RNAV umbrella encompasses many different technologies, from GPS/GNSS satellite-based systems to VOR or DME ground-based systems. The LORAN ground stations have since been decommissioned. These systems featured airport and NAVAID databases that could be used basically like a GPS. LORAN used low-frequency and long-range radio signals to create very accurate aircraft position fixes. LORAN-C, the most advanced version, relied on ground radio stations to fix its position in latitude and longitude. LORANĪnother precursor to GPS-based RNAV systems was LORAN. With advances in small laser accelerometers, avionics manufacturers are eyeing small, affordable units that combine with GPS data to provide position information even when GPS signals become unreliable. But the technology is not only expensive, but it’s also large and bulky. These units have been used for decades on airliners and business jets. When combined with ground-based navigation systems like DME, these systems can maintain their position fixing indefinitely. So, for example, a trans-Atlantic flight could depart from an airport and cross the ocean with only a 0.4 NM error, all with no outside help! To add to system redundancy and to further increase their accuracy, INS/IRS units typically also receive VOR or DME signals. INS, and their newer cousins IRS (inertial reference systems), are incredibly accurate, with errors of only 0.4 NM after four to six hours of flying. Many large airplanes contain two units so that they can compare their results and compensate for any errors. No ground radio stations are necessary after the system gets an initial fix. These systems contain gyros that sense aircraft movement, so navigation is wholly based on measurements taken inside of the aircraft. One of the coolest RNAV systems around is INS (inertial navigation system). More advanced aircraft could carry more sophisticated and expensive avionics systems. This is easy to decipher on any aeronautical chart. When a specific location is written down, for example, to depict a flight restriction or obstacle, the VOR-radial-distance is often given. While those early VOR/DME RNAV systems are few and far between these days, the location coding of phantom waypoints is still used throughout aviation. The aircraft could then be flown directly to this point as if that’s where the ABC VOR was located. For example, the pilot could program a waypoint 20 miles south of the ABC VOR by programming it as ABC180020.0 (VOR-radial-distance). Avionics manufacturers created systems that would use existing VORs and DMEs to create phantom waypoints. Early Area Navigation Systems VOR/DME RNAVīefore GPS came along, two other RNAV systems enjoyed popularity. The resultant path is seldom a straight line between the departure point and the destination. This has meant flying directly to or directly away from a VOR or NDB radio station on the ground. If you remove the use of visual landmarks, instrument pilots are entirely reliant on electronic navigation sources. Being able to use physical landmarks they can see is a big help. They may have to make a few miles diversion for airspace or obstacles, but they can generally use any points they desire along the way. VFR pilots have always been able to go directly to their destination. The most common type of RNAV equipment today is GPS, but several older technologies have been in use on larger aircraft for decades. Area navigation is the ability to navigate directly between any two points on earth. RNAV stands for “area navigation” in aviation.
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