(7)  
The selection of either the VOR/ILS or the INS to drive the HSI radio navigation displays is controlled by the captain's and first officer's VOR/ILS-INS switches. The switches control the captain's and first officer's RADIO/INS relays in the same manner as the VOR switches control the VOR/ILS A and B transfer relays.

 H. Functional Description, Antenna Switching (Fig. 5)
 (1)  
Radio frequency signals from the VOR and localizer antennas are applied to the three VOR/ILS receivers. VOR and localizer rf is switched to the receivers as determined by the mode selector switch on the AP/FD NAV mode selector panel and the position of the captain's and first officer's VOR/ILS A transfer relays. RF switches 1, 2, and 3 direct rf from the VOR antenna to the receivers when the mode switch is in the INS, HDG, or VOR LOC position and rf from the localizer antennas when the mode switch is in the LAND or ILS position after localizer capture has occurred. RF switches 4 and 5, controlled by the VOR/ILS A transfer relays, direct the VOR/LOC rf to the two receivers that are in use.

 (2)  
On XA ALL EXCEPT AZ 221-299; SN 351-399; IB 406-499; and AT airplanes, glide slope rf is fed to the three VOR/ILS receivers through hybrid couplers from two capture antennas and one track antenna in each aft nose wheel well door. Relative positions of the landing gear (doors closed or open) changes the polarity of the glide slope antennas essentially selecting the capture antennas when the aft wheel well doors are closed and the track antenna when the doors are open.

 (3)  
On AT ALL, glide slope rf for VOR/ILS receivers No. 1 and 2 is selected by the coaxial relays from either the capture antenna in the nose radome or the track antenna in the leading edge of each aft nose wheel well door. Glide slope rf for VOR/ILS receiver No. 3 is hard wired to the track antenna in the left aft nose wheel well door.

 (4)  
On AZ 221-299; SN 351-399; IB 406-499,

 EFFECTIVITY
 AZ ALL
 AT ALL

 IB ALL  CONFIG 2 SN ALL  01 Page 23  Oct 25/97

34-31-00
 glide slope rf for VOR/ILS receivers No. 1 and 2 is selected by the coaxial relays from either the capture antenna in the nose radome or the track antenna in the leading edge of each aft nose wheel well door. Glide slope rf for VOR/ILS receiver No. 3 is through a third coaxial relay. Relay No. 3 selects either the second capture antenna in the nose radome or the track antenna in the left aft nose wheel well door for VOR/ILS receiver No. 3.
 (5)  
The coaxial relays are controlled by transistor switching logic in the primary and alternate landing gear logic units. Relay No. 3 is controlled by transistor switching logic in autopilot accessory box No. 3 and in the primary and alternate landing gear logic units. The relays are energized to complete the glide slope capture antenna configuration when the landing gear are up and glide slope 28-volt dc power is available. When the landing gear are down, the relays are de-energized, to open the rf line between the capture antennas and the VOR/ILS receivers. This leaves the VOR/ILS receiver glide slope rf input connected to only the glide slope track antenna eliminating spurious capture signals which cause loss of glide slope capture when in track antenna configuration and the airplane is flown at high bank angles.

 (6)  
Glide slope antenna test switches and associated annunciators on the pilots' center instrument panel (P2) provide a means for checking coaxial relay operation. Pushing an ANT TEST switch completes a ground through logic circuits in AP accessory box No. 1 or 2. This energizes the coaxial relay causing the associated annunciator to come on and the selection of the capture antenna as an rf signal source for the receiver(s). The logic circuits inhibit the VOR/ILS test circuits whenever the AFCS is operating in VOR/LOC, ILS or LAND mode and channel A, B or C of the AFCS is in command.

 I.  Functional Description, Data Switching (Fig 6) (XA ALL EXCEPT AT airplanes)
 (1)  
All signals which interface with the three VOR/ILS receiver (except rf from the antennas) pass through the VOR/ILS relays. With the VOR/ILS deviation transfer switch in the normal position the captain's VOR/ILS relay is in position No. 1 and the first officer's VOR/ILS relay is in position No. 2. In this mode input data, power, and control signals are applied to receivers No. 1 and 2. The outputs from receiver No. 1 are applied to the captain's instruments while the first officer views data from receiver No. 2.

 (2)  
In an alternate configuration receiver No. 3 sends data to either the captain's or first officer's instruments dependent upon the position of the VOR/ILS transfer switch.

 J.  Functional Description, Data Switching (Fig 6) (AT ALL)
　
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