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(4) Local Station - This catalog contains a list of the twenty (or fewer) closest VORTAC stations in the vicinity of airplane present position. It is assembled from all other catalogs. Retrievable data includes latitude, longitude, magnetic variation, frequency, altitude, and class of each station in the catalog.
E. When three inertial navigation systems are installed, the INS features crossfill and triple-position mixing. Crossfill allows waypoint information entered into one system to be transferred into the other two systems. Triple mixing provides for the mixing and display of computed position of all three systems.
F. VORTAC (VOR/DME) position updating of the inertial navigation system allows the system to be operated as a radio navigation (R-NAV) system. The VORTAC station may be manually tuned at the VHF navigation control panel or automatically tuned by the inertial navigation unit.
G. From the airplane present position latitude and longitude coordinates the INS calculates magnetic variation. When the INS approach mode is enabled the magnetic variation is used to change the normal INS true north reference to magnetic north reference. This allows computation and display of magnetic heading, magnetic track and magnetic desired track without utilizing inputs from the magnetic compass system.
4. VORTAC Radio Position Update (Fig. 5)
____________________________
A. The inertial navigation system present position can be automatically updated using inputs of range from the DME system and omnibearing from the VHF navigation receiver. The update mode is enabled at the CDU. The un-updated position is maintained separate from the updated position and may be restored at any time. The VHF navigation control panel may be used to manually tune a VHF navigation receiver to a VORTAC station, or the navigation receiver may be automatically tuned by the INS.
B. System present position, in latitude and longitude coordinates, is computed from the INS position and the latitude and longitude update of DME and VOR. The updates are corrected by sequential measurements of DME range and VOR omnibearing. Airplane barometric altitude is used to reduce the DME slant range to the equivalent ground range.
C. The INS INU contains VORTAC station data that is used for radio updating of INS present position during a flight.
D. Automatic tuning
(1) In the autotune mode, the INU computer scans the VORTAC station data in the INU, to select the closest station and set the tuning lines to the 2 x 5 code of this closest station. As the airplane progresses along the selected route, it will fly away from the selected station and become closer to a different station. When this happens, the INU automatically selects the new station and tunes the navigation receivers.
E. Manual tuning
(1) VORTAC station frequency is selected at the manual tuning head in the VHF navigation control panel. In the manual mode VORTAC station data stored in the INU is scanned by the computer, to select the closest station with the same frequency as that selected on the VHF navigation control panel.
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A
ON AIRPLANES WITH LTN-72RL INS, ANNUNCIATOR READS READY NAV
INS Mode Selector Unit Figure 6
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F. The captain's and first officer's inertial navigation systems are each connected to a VOR receiver and a DME interrogator. Interchange of DME data via the intersystem data bus enables dual DME update, since an INS may update using data from the DME connected to that particular INS, together with data from a DME connected to another INS.
5. Radio Update Mode_________________
A. When the INS is initially turned on automatic radio updating is inhibited. Control of the update mode is provided at the CDU. The control is divided into the following categories:
(1)
Enable RNAV
(2)
Disable RNAV
(3)
Flush
(4)
Inhibit VOR
(5)
Inhibit DME 2
(6)
Enable TMIX
(7)
Disable TMIX
B. After the RNAV mode is enabled, the following update status modes are available:
UPDATE STATUS_____________ UPDATE STATUS/SOURCE
1.
___ ___ ___ RNAV not enabled/INS
2.
___ ___ ___ RNAV enabled, no update/INS
3. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航2(130)
