Long Range Navigation (LORAN) is a type of RNAV that is no longer in operation in the United States. It was developed during World War II, and the most recent edition, LORAN-C, was very useful and accurate for aviators as well as mariners.
LORAN uses radio wave pulses from a series of towers and an onboard receiver/computer to positively locate an aircraft amid the tower network. There are twelve LORAN transmitter tower “chains” constructed across North America. Each chain has a master transmitter tower and a handful of secondary towers.
All broadcasts from the transmitters are at the same frequency, 100 kHz. Therefore, a LORAN receiver does not need to be tuned. Being in the low frequency range, the LORAN transmissions travel long distances and provide good coverage from a small number of stations.
Precisely-timed, synchronized pulse signals are transmitted from the towers in a chain. The LORAN receiver measures the time difference between received pulses from the master tower and two other towers in the chain. It calculates the aircraft’s position based on the intersection of hyperbolic curves representing elapsed signal times from each of these known points.
The accuracy and proliferation of GPS navigation has caused the U.S. Government to cease support for the LORAN navigation system citing redundancy and the expense of operating the towers as reasons for the decision.
The LORAN chain in the Aleutian Islands shared with Russia was the only LORAN chain that had not yet been scheduled for closure. Panel-mounted LORAN navigation units will likely be removed and replaced by GPS units in aircraft that have not already done so. [Figure 1]
 |
| Figure 1. Panel-mounted LORAN units are now obsolete as LORAN signals are no longer generated from the tower network |
How did a LORAN-C receiver calculate the aircraft's position?
Why was the LORAN system decommissioned in the United States?
RELATED POSTS