737 AMM 飞机维护手册 导航 NAVIGATION 2(21)

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8.  Control Panel
A.  The controls for each navigation unit are on separate VHF NAV/COMM control panels. The controls on the VHF NAV section of each panel consist of a volume control, two frequency selector knobs with associated frequency display, a NAV TEST switch with VOR test button, and a combination DME function selector and test switch.
9.  VHF NAV Transfer Switch
A.  A toggle actuated transfer switch is installed in the VHF NAV and COMPASS instrument switching module located on the overhead panel. The switch controls the associated VHF NAV transfer relays which enables either VOR/ILS system to feed both captain's and first officer's indicator's, flight director computers and the autopilot.
10.  VHF NAV Transfer Relays
A.  The transfer relays are stepping type relays. When the VHF NAV transfer switch is in the NORMAL position, the captain is on system No. 1 and the first officer is on system No. 2. Placing the VHF NAV transfer switch to BOTH ON 2 position supplies a ground through the contacts of the VHF NAV transfer switch, transfer relay No. 2 and transfer relay No. 1 to the coil of nav transfer relay No. 1. This momentarily energizes transfer relay No. 1 and the relay steps to the BOTH ON 2 position. Positioning the VHF NAV transfer switch back to the NORMAL position, again momentarily energizes transfer relay No. 1 and the relay steps back to the normal position. The first officer's transfer relay is controlled in the same manner as the captain's by positioning the VHF NAV transfer switch to BOTH ON 1.
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11.  HSI Transfer Switch
A.  Two HSI transfer switches with RADIO--NAV positions are installed on the pilots' lightshield panel. The switches control the radio/ONS relays to enable the captain and first officer to select course presentation from the VOR/ILS navigation system or the OMEGA navigation system (ONS).
12.  Radio/ONS Transfer Relays
A.  Two radio/ONS transfer relays are installed in rack E3. The relays connect the HSI course deviation, to-from and nav warning displays to the VOR/ILS navigation systems as shown in Fig. 3.
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13.  Flight Instrument Accessory Unit
A.  A flight instrument accessory unit is located in electronic equipment rack E-1. The unit contains relays and printed circuit for signal conditioning and interface between the navigation systems and the flight instruments. In addition, the unit contains a solid-state circuit for automatic dimming of the approach progress display lights in the flight director system.
B.  The flight instrument accessory unit circuits associated with the VOR/ILS navigation system consist of the diodes across the coils of the transfer relays and the VOR/ILS receiver deviation and flag warning output loading resistors.
14.  AFCS Accessory Box
A.  The AFCS accessory box is mounted on the E1-3 shelf in the electrical and electronic equipment bay. The unit is a 1/3 ATR long unit which is retained in the rack by a cam-lock handle which engages in a rack-mounted adjustable swivel bolt. Electrical connections are provided by a DPX connector on the rear of the unit which mates with a rack-mounted connector.
B.  The unit contains numerous relays, time delay gates, a circuit interrupter and other components used for interconnecting the AFCS system.
C.  The AFCS accessory box circuits associated with the VOR/ILS navigation system consist of two relays for inhibiting the VOR/ILS self-tests when the autopilot is operating in a radio mode and the mode logic for enabling ILS relays No. 1 and No. 2.
15.  Operation
A.  Frequencies in the VOR/LOC bands are selected by rotating the frequency selectors on the control panel. The audio output is available through the interphone system.
B.  Taking one system as an example: position of the course deviation bar with respect to the miniature airplane, shows real airplane position with respect to the selected course. The course deviation scale dots are reference points for showing airplane angular displacement from the selected course. TO-FROM indication is shown by a broad arrow which appears from behind the course deviation scale in the center of the HSI. As the airplane passes over the selected VOR ground station, the annunciation reverses 180 degrees.
　
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