FIG ENR 4.1.11
First Line.of.Position
16.4.2.1 The first TD will locate an aircraft somewhere on a line.of.position (LOP) on which the receiver will measure the same TD value.
16.4.2.2 A second LOP is defined by a TD measurement between the Master station signal and the signal form another secondary station.
FIG ENR 4.1.12
Second Line.of.Position
16.4.2.3 The intersection of the measured LOPs is the position of the aircraft.
FIG ENR 4.1.13
Intersection of Lines.of.Position
16.4.3 The navigation computer converts TD values to corresponding latitude and longitude. Once the time and position of the aircraft are established at two points, distance to destination, cross track error, ground speed, estimated time of arrival, etc., can be determined. Cross track error can be displayed as the vertical needle of a course deviation indicator, or digitally, as decimal parts of a mile left or right of course.
16.5 Notices to Airmen (NOTAMs) are issued for LORAN chain or station outages. Domestic NOTAM (D)s are issued under the identifier “LRN.” International NOTAMs are issued under the KNMH series. Pilots may obtain these NOTAMs from FSS briefers upon request.
16.6 LORAN Status Information. To find out more information on the LORAN system and its operational status you can visit the website http://www.navcen.uscg.gov/loran/default.htm or contact NAVCEN’s Navigation Information Service (NIS) watchstander, phone (703) 313.5900, fax (703) 313.5920.
NOTE.
In accordance with the 2010 DHS Appropriations Act, the
U.S. Coast Guard (USCG) terminated the transmission of all U.S. LORAN.C signals on 08 Feb 2010. The USCG also
Federal Aviation Administration Twentieth Edition
terminated the transmission of the Russian American signals on 01 Aug 2010, and the Canadian LORAN.C signals on 03 Aug 2010. For more information, visit http://www.navcen.uscg.gov. Operators should also note that TSO.C60b, AIRBORNE AREA NAVIGATION EQUIPMENT USING LORAN.C INPUTS, has been canceled by the FAA.
16.7
LORAN’s future. The U.S. will continue to operate the LORAN system in the short term. During this time, the FAA LORAN evaluation program, being conducted with the support of a team comprising government, academia, and industry, will identify and assess LORAN’s potential contributions to required navigation services for the National Airspace System (NAS), and support decisions regarding continued operation of the system. If the government concludes LORAN should not be kept as part of the mix of federally provided radio navigation systems, it will give the users of LORAN reasonable notice so that they will have the opportunity to transition to alternative navigation aids.
17.
Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS)
17.1 IRUs are self.contained systems comprised of gyros and accelerometers that provide aircraft attitude (pitch, roll, and heading), position, and velocity information in response to signals resulting from inertial effects on system components. Once aligned with a known position, IRUs continuously calculate position and velocity. IRU position accuracy decays with time. This degradation is known as “drift.”
17.2 INSs combine the components of an IRU with an internal navigation computer. By programming a series of waypoints, these systems will navigate along a predetermined track.
17.3
AHRSs are electronic devices that provide attitude information to aircraft systems such as weather radar and autopilot, but do not directly compute position information.
18.
Global Positioning System (GPS)
18.1 System Overview
18.1.1 System Description. The Global Positioning System is a satellite.based radio navigation system, which broadcasts a signal that is used by receivers to determine precise position anywhere in the world. The receiver tracks multiple satellites and determines a pseudorange measurement that is then used to determine the user location. A minimum of four satellites is necessary to establish an accurate three.dimensional position. The Department of Defense (DOD) is responsible for operating the GPS satellite constellation and monitors the GPS satellites to ensure proper operation. Every satellite’s orbital parameters (ephemeris data) are sent to each satellite for broadcast as part of the data message embedded in the GPS signal. The GPS coordinate system is the Cartesian earth.centered earth.fixed coordinates as specified in the World Geodetic System 1984 (WGS.84).
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