K.  Functional Description, ILS No. 3 Fail-Op Annunciators (AZ 221-299; SN 351-399; IB 406-499; AT ALL)
 (1)  Flag signals to drive the G/S-3 and LOC-3 fail-op annunciators originate within VOR/ILS receiver No. 3 as shown in Fig. 7. The annunciators display either a black (valid) or red (invalid) ILS mode of operation for receiver No. 3.
 EFFECTIVITY
 AZ ALL
 AT ALL

 IB ALL  CONFIG 2 SN ALL  01 Page 67  Oct 25/97

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 VOR/ILS NAVIGATION SYSTEM - DESCRIPTION AND OPERATION
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 1.  General
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 A.  Two VOR/ILS (VHF omnidirectional range/instrument landing systems) navigation systems and a switchable 3rd receiver are installed. A system consists of a VHF NAV control panel, a VOR/ILS receiver, transfer switching, antenna switching, and displays on flight instruments. A VOR antenna, two localizer antennas, and three glide slope antennas (two track and one capture) provide radio frequency inputs to the receivers. Either the VOR or the LOC antenna is selected by means of the A/P-F/D mode logic circuits. Figure 1 shows the location of each of the units associated with the VOR/ILS navigation system while systems interface is shown in Fig. 6.
 B.  The VOR/ILS navigation system determines airplane bearing with respect to ground-based VOR stations and airplane position with respect to a selected VOR radial, or to an ILS approach path. This data is provided to the autopilot/flight director (A/P-F/D) system and to displays on the captain's and first officer's instrument panels. Glide slope deviation data is also provided to the ground proximity warning system computer.
 C.  Airplane magnetic bearing to the VOR ground station signals received is determined by the VOR portion of the system. The ILS portion of the system provides lateral and vertical deviation information with respect to a radio beam positioned above runways for landing guidance.
 D.  Power is applied to the VOR/ILS navigation systems through circuit breakers located on overhead circuit breaker panels P7 and P126.
 2.  VHF NAV Control Panel (Fig. 1)
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 A.  Each VHF NAV control panel, located on the pilots' lightshield panel (P10), consists of frequency selector knobs, a frequency indicator, and a VOR/ILS self-test switch. DME system controls are also located on the control panel (Ref 34-55-00, Description and Operation).
 B.  The control panel provides manual VOR or localizer frequency selection. The glide slope receiver is co-tuned when a localizer frequency is selected. Frequency control is in the 108.00-MHz to 117.95-MHz range. Localizer frequencies extend from 108.10 MHz to 111.95 MHz on the odd tenths megahertz. Glide slope frequencies range from 329.3 MHz to
 335.0 MHz and are paired with the localizer frequencies. VOR frequencies extend from 108.00 to 118.00 MHz except for the localizer frequencies.
 C.  The larger knob of the frequency selector switch provides frequency selection in the units, tens and hundreds range. The smaller knob provides frequency selection in fractions (tenths and hundredths of a MHz).
 D.  The frequency indicator displays the operating frequency of the VOR or localizer circuits of the VOR/ILS receiver.
 E.  The VOR/ILS test switch provides a self-test capability for the VOR/ILS receiver and associated displays.
 3.  VOR/ILS Receiver
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 EFFECTIVITY

 AF 121, 122, 155-171,  CONFIG 3 174-190, 195-199;  01 Page 1 VM ALL  Sep 25/94

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 A.  Three VOR/ILS receivers containing planar construction-type circuit boards and an interconnect unit are installed on shelves E1-2 and E1-3 in the main equipment center. All interconnections are made through a dual multi-pin connector on the rear of the chassis. A test connector is also mounted on the rear of the unit for testing and fault analysis.
 B.  Each VOR/ILS receiver consists of VOR/LOC and glide slope receiver assemblies with associated instrumentation, monitoring and self-test circuit board assemblies, an RMI driver and a power supply. These assemblies process VOR, localizer and glide slope signals and provide outputs to drive deviation, flag and to-from flight instrument displays.
 4.  VOR Antenna
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 A.  The VOR antenna is a dual, pedestal-mounted, V-type unit, supplying the VOR/ILS receivers with rf received from the VOR stations. The antenna is located beneath a vertical fin cap and is accessible through an access door in the vertical fin. Independent outputs of the VOR antenna are supplied to the VOR/LOC antenna switches for distribution to the receivers.
 B.  On AF 121 and 122, the antenna is accessible only after removing the vertical fin cap.
　
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