時間：2011-04-18 00:47來源：藍(lán)天飛行翻譯 作者：航空 點擊：次
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6.LORAN signals operate in the low frequency band (90.110 kHz) that has been reserved for marine navigation signals. Adjacent to the band, however, are numerous low frequency communications transmitters. Nearby signals can distort the LORAN signals and must be eliminated by the receiver to assure proper operation. To eliminate interfering signals, LORAN receivers have selective internal filters. These filters, commonly known as “notch filters,” reduce the effect of interfering signals. 7.Careful installation of antennas, good metal. to.metal electrical bonding, and provisions for precipitation noise discharge on the aircraft are essential for the successful operation of LORAN receivers. A LORAN antenna should be installed on an aircraft in accordance with the manufacturer’s instructions. Corroded bonding straps should be replaced, and static discharge devices installed at points indicated by the aircraft manufacturer. d. LORAN Navigation 1. An airborne LORAN receiver has four major parts: (a)Signal processor; (b)Navigation computer; (c)Control/display, and (d)Antenna. 2. The signal processor acquires LORAN signals and measures the difference between the time.of.arrival of each secondary station pulse group and the Master station pulse group. The measured TDs depend on the location of the receiver in relation to the three or more transmitters. Navigation Aids 1.1.23 FIG 1.1.16 First Line.of.Position (a)The first TD will locate an aircraft somewhere on a line.of.position (LOP) on which the receiver will measure the same TD value. (b)A second LOP is defined by a TD measurement between the Master station signal and the signal from another secondary station. FIG 1.1.17 Second Line.of.Position (c) The intersection of the measured LOPs is the position of the aircraft. FIG 1.1.18 Intersection of Lines.of.Position 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. e. 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. f. LORAN status information. To find out more information on the LORAN system and its operational status you can visit 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. g. 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 1.1.24 Navigation Aids 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. 1.1.16. VHF Direction Finder a.The VHF Direction Finder (VHF/DF) is one of the common systems that helps pilots without their being aware of its operation. It is a ground.based radio receiver used by the operator of the ground station. FAA facilities that provide VHF/DF service are identified in the A/FD. b.The equipment consists of a directional antenna system and a VHF radio receiver. c.The VHF/DF receiver display indicates the magnetic direction of the aircraft from the ground station each time the aircraft transmits. d.DF equipment is of particular value in locating lost aircraft and in helping to identify aircraft on radar. REFERENCE. AIM, Direction Finding Instrument Approach Procedure, Paragraph 6.2.3. 1.1.17. Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS)a. 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.” b.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. AIM c. AHRSs are electronic devices that provide attitude information to aircraft systems such as weather radar and autopilot, but do not directly compute position information. 1.1.18. Doppler Radar Doppler Radar is a semiautomatic self.contained dead reckoning navigation system (radar sensor plus computer) which is not continuously dependent on information derived from ground based or external aids. The system employs radar signals to detect and measure ground speed and drift angle, using the aircraft compass system as its directional reference. Doppler is less accurate than INS, however, and the use of an external reference is required for periodic updates if acceptable position accuracy is to be achieved on long range flights. |
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