This type of navigation allows a pilot to fly a selected course to a predetermined point without the need to overfly ground-based navigation stations. Flight can be from waypoint to waypoint. A waypoint is a position determined either by Latitude/Longitude or Radial and distance from a VORTAC or VOR/DME station.

These navigation receivers use VOR/DME or VORTAC stations as a base point. A waypoint is defined as a distance along a radial of the VOR. The RNAV equipment electronically translates (moves) the VOR station to the waypoint position. You then fly the VOR as though it were located at the waypoint’s geographical location.

Through triangulation, the navigation unit measures the radial and distance of leg A. By knowing the entered data for leg B, the azimuth and distance to the waypoint along path C is repeatedly calculated calculated. It is as though the VOR were located at the waypoint position.

The LORAN unit can indicate:

Present Position - in Latitude/Longitude and/or relative to a destination, waypoint or checkpoint.
Bearing and distance to your destination.
Groundspeed and estimated time enroute.
Course Deviation Indicator.
Storage in memory of all US airports, pilot selected fixes, minimum enroute and obstruction clearance altitudes, and Class B and C airspace warnings.
Continuous computation of bearings and distances to the nearest airports. Computation of wind direction and velocity.
Add ons, such as fuel flow analyzers to estimate fuel needed to reach destination and alternates; ELT’s to transmit exact location of ELT.

Add-on programmable and updatable databases.

Since LORAN operates on a low-frequency signal, it is subject to the same disturbances that AM radio sustains. It is possible to loose signal when operating near thunderstorm and in heavy rain areas.

The LORAN receivers know the frequency of the Master and secondary stations; no tuning by the pilot is necessary.

Global Positioning System (GPS)

The GPS system is the latest in technology that can be used by aircraft. It has many of the attributes of LORAN. The complete system will contain up to 21 satellites in earth orbit. The "clocks" and "positional data" is updated periodically to insure accuracy of the data from the satellites. It sense 4 or more satellites in orbit. The system is maintained by the US Department of Defence.

Like LORAN, it operates on a time-based methodology. Each satellite transmits coded pulses indicating it’s position, and the precise time the pulses are sent. The GPS unit listens to the satellite’s signal, and measures the time between the satellites transmission and receipt of the signal. By the process of triangulation among the several satellites being received, the unit computes the location of the GPS receiver. Not only can Latitude and Longitude be calculated, but altitude as well.

Like LORAN, the GPS unit contains data about all the commercial airports in the US, including runway lengths, directions, and location. There are numerous forms of display among the various manufacturer. The units can range from “hand held” to “panel mount” with altitude information input from an encoding altimeter. They can warn of Class B, C, and Prohibited and Restricted airspace. They can calculate direction and time to nearest suitable alternate airports in event of emergency.

The database in most units can be updated via a connection to a Personal Computer. The maximum error is within 100 meters (0.05 Nm). Work is in progress to give the GPS system adequate precision for instrument approaches.

No frequency tuning is required, as the frequency of the satellite transmissions are already known by the receiver.

Work is currently underway to provide sufficient accuracy for use of GPS for instrument approaches.