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directly from the compass card. More sophisticated instruments of later design automatically rotate the compass
card of the instrument to agree with the magnetic heading of the aircraft. Thus MB to the station can be read at
any time without manually rotating the compass card on the ADF face.
Area Navigation
Three types of navigation receivers can be called Area Navigation. They are:
· RNAV
· LORAN
· GPS
RNAV
This type of navigation allows a pilot to fly a selected course to a predetermined point without the need to overfly
Navigation
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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 VOdistance along a radial of the VOR. The RNAV eqthe waypoint position. You then fly the VOR as 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.
Long Range Navigation (LORAN)
LORAN operates on the principle of time meastransmit a synchronized pulse. The time diffpulses is measured. From this data, the comwithin 0.25 Nm or better. The North East LORfacilities can be loaded into the memory of thThe 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.
Navigation
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· 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.
For more technical data about LORAN see, Loran C General LORAN Information. Also see Aeronautical
Information Manual AIM 1-17. LORAN
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 Defense. See an GPS Overview Pictoral for a general concept of the GPS
system. See GPS Constellation to see the satellite orbits.
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. See Geodetic Coordinate System for a pictoral showing how the
GPS system can indicate these 3 parameters of LAT, LON, and HEIGHT.
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.
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