(5)
A mode switch which put both transponders in standby mode, or activates the selected transponder.
3. ATC Transponder (Fig. 1)
_______________
A. The ATC transponders are located on the E2 electronic equipment rack. The left (No. 1) transponder is located on shelf E2-2. The right (No. 2) transponder is located on shelf E2-3.
B. The active ATC transponder transmits a coded reply when it is
interrogated by an ATC ground station.
C. The TCAS compatible Mode S transponder receives interrogations from the ATC ground station and TCAS equiped airplanes.
D. Both transponders are identical to each other. Each transponder has the following switches and indicators:
(1)
A green XPDR PASS indicator light which comes on when a transponder self-test is successful
(2)
A red XPDR FAIL indicator light which comes on when a transponder self-test detects a fail
(3)
A red TOP ANT indicator light which comes during a self-test when the upper antenna impedance is incorrect
(4)
A red BOT ANT indicator light which comes during a self-test when the lower antenna impedance is incorrect
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(5)
A red ALT SIG indicator light which comes on when the altitude input source indicates a barometric altitude failure
(6)
A red CTL PNL indicator light which comes on when there is a failure of the control input
(7)
A TEST switch which a starts a transponder self-test.
4. ATC Antenna
___________
A. Two ATC antennas are installed in the airplane. The antennas are on the top and the bottom the airplane. Two rf switching relays connect both antennas to the active transponder. The top antenna is located on the centerline of the fuselage at station 610. The bottom antenna is located on the centerline of the fuselage at station 570. The antennas are omnidirectional L-blade type antennas. Each antenna can transmit and receive signals for the active transponder. The active transponder automatically uses the antenna with the greatest signal strength.
5. ATC Interfaced Systems
______________________
A. Central Maintenance Computer System (CMCS)
(1)
The component of the CMCS which is connected to the ATC system is the Central Maintenance Computer (CMC).
(2)
The CMCS provides these functions to the ATC system:
(a)
The CMCS records ATC equipment failures for present and past faults
(b)
The CMCS provides selection and display of maintenance pages which display equipment faults
(c)
The CMCS provides ground test functions to initiate Built-In Test Equipment (BITE) tests of the ATC system and display the results on the Control Display Unit (CDU).
(3)
Two ARINC 429 buses connect the transponders to the two Central Maintenance Computers (CMCs).
6. Operation
_________
A. Mode-A and Mode-C
(1)
There is no power switch on the ATC control panel. Power is applied to the system when the ATC L and ATC R circuit breakers on the P7 panels are closed. Power is aplied to both ANTENNA TRANSFER RELAYs when the ATC ANTENNA SW circuit breaker on the P7 panel is closed.
(2)
The desired ATC system (left or right) is set with the transponder select switch. The L position causes the control panel to send an ON discrete to the left transponder if the AIR/GND RELAY is in AIR mode and the mode switch is set to XPNDR. The R position causes the control panel to send an ON discrete to the right transponder if the AIR/GND RELAY is in AIR mode and the mode switch is set to XPNDR. The STBY position causes the control panel to send a STANDBY discrete to both transponders.
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