RNAV-Random or Area Navigation basics
RNAV avionic system is a short range navigational aids and it stands for Random Navigation or Area Navigation. It provides Aircraft bearing and distance with reference to a 3D artificial reference point known as Waypoint(WPT). In fact, the main motivation to navigate using computerized WPTs is to obtain optimized air routes from departure to arrival.
To obtain WPTs, we need present Aircraft 3D position fix.
There are three ways to do that using any of the following ways.
1. Ground stations such as VOR-DME or VORTAC to obtain bearing and distance. These can be converted to obtain Aircraft latitude and longitude information. Radio altemeter in the Aircraft radar is used to obtain the aircraft altitude.
2. Aircraft self contained systems such as INS and DNS
3. Orbital Satellite systems such as GPS.
In the Aircraft, RNAV system performs following tasks.
• RNAV calculates WPTs or uses already loaded WPTs from a NAV Database based on the present Aircraft position and the flight plan required to reach destination.
• Once the WPT is identified in 3D, then the Aircraft bearing and distance is obtained. Now Aircraft can fly toward the WPT.
Some RNAV systems also outputs following parameters.
• Estimated Time of Arrival to next WPT
• Necessary IAS required to achieve ETA
• Fuel consumption
INS or DNS or GPS facilitates use of RNAV in the oceanic airspace as no stations are needed.
• With RNAV more direct, efficient and flexible routes are generated.
• Arrives faster at the destination.
• It is cost effective.
• More traffic is possible at random locations and hence less traffic is obtained in a specific geographical area.
• Full use of airspace can be obtained.
• Same errors as occurred in VOR, DME and VORTAC systems.
• Possible way to obtain fictitious WPTsis through corresponding Ground stations; however they are limited by the operational range.
• The airway obtained using RNAV is tighter than V and J airway. With RNAV, airway width is about 8nm (or 15km); while with V or J airway the width is about 10sm (or 16km).
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