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LORAN-Long Range Navigation basics

LORAN-C avionic system is a long range navigational aids and it stands for Long Range Navigation revision C. The system provides A/C position fix in 2-dimentional. In fact, this technology is known as a hyperbolic system since it determines NAV fix using hyperboles or parabolic lines generated from the intersection of signals radiated by ground stations.

LORAN,Long Range Navigation

To obtain the Aircraft position fix at least 2 hyperbolic grids are required. This means that at least two Line of Position have to be generated from a single master station and at least two slave ground stations. The same has been depicted in the figure-1.

On the ground station following are the specifications of LORAN:
•  Master and slave LORAN -C Transmit systems.
•  Frequency of operation is low frequency from 90 to 110KHz.
•  LORAN-C signal pulses propagate using Ground waves.
•  Possible Tx topologies of LORAN system are as follows:
Trial consisting of 1 master and 2 slave stations
Star consisting of 1 master and 3 slave stations
Square consisting of 1 master and 4 slave stations
•  The master station transmits a sequence of 9 pulses.
•  After a delay, the slave station will emit a sequence of 8 pulses.

LORAN C airborne

•  In the Aircraft, LORAN-C receive system works at the LF frequency.
•  Highly selective receiver in order to avoid interference from the other signals.
•  When the 9 pulses from the master station reaches the Aircraft, the receiver will start counting the time it takes for the slave 8 pulses to reach the airborne receiver.
•  To calculate the aircraft position fix, we need to know the position of the master and slave stations, the station separation distance and δt.
•  There exist receiver with dual LORAN-C and GPS usage. The processor within this receiver will calculate and output following parameters.
•  Aircraft position with latitude and longitude
•  GS
•  Wind drift
•  WPT information
•  ETAs
•  Airport data


•  LORAN-C does not suffer from LOS since it operates at LF band.
•  Hyperbolic grid NAV provides a more direct route similar to WPT NAV.
•  Signal propagation is based on GND waves; therefore large travel ranges are possible.


•  Error will be about +/- 150 m.
•  Ground wave propagation error, the velocity at which the signal travels may vary, and hence some offset may be introduced in calculating the aircraft position fix.
•  There are not enough LORAN-C ground stations in the world to cover all possible air routes.

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