LOOP 2 FIRE DETECTORS ON
AUTOMATIC FIRE/OVHT LOGIC TEST CARD (AFOLTS)
APU FUEL
28V DCCNTL RELAY
HOT BAT

LOOP 2 APU FIRE DETECTOR CARD OFF BUS FIRE EXT APU
APU START SW
P6

APU BOTTLE
DISC RELAY
28V DC
BAT BUS

REMOTE FIRE
IND APU

P11
28V DCENG/APU/CARGOTEST SW
TEST RELAY
APU Fire Detection Schematic
Figure 2 (Sheet 2)

EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH SYSTRON DONNER FIRE ú

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MAINTENANCE MANUAL

 B.  Functional Description (Systron Donner)_______________________________________
 (1)  
With 28-volt dc power applied to the system, current is sent from each control card to the detectors in the corresponding loop. Each detector element has a resistance value, and is in parallel with the other elements in its' loop. Thus, each loop has an equivalent resistance value, and the control card senses a loop voltage potential.

 (2)  
When a detector element pressure switch opens (integrity switch) or closes (alarm switch), the equivalent loop resistance is changed, and the voltage sensed by the control card changes. The card determines which signal is sensed, and sends an appropriate (alarm or fault) signal to the AFOLTS card.

 (3)  
The AFOLTS card configures the control card signals in AND logic, and determines the appropriate output to flight and ground crews. The Logis System Operation table shows the normal operating mode.

 ~.....................................
 | Logic System Operation |
 | APU Fire Detection Loops |
 | Logic AND Configuration |
 | Table 1 |
 .......................................
 | | AFOLTS OUTPUTS |
 | ..................
 | INPUTS TO AFOLTS | FIRE DETECTION |
 | LOOP 1 LOOP 2 | SYSTEM |
 .......................................
 | ALARM ALARM | FIRE |
 .......................................
 | ALARM -----| EICAS LOOP 1 |
 .......................................
 | ALARM FAULT | FIRE |
 .......................................
 | -----ALARM | EICAS LOOP 2 |
 .......................................
 | FAULT ALARM | FIRE |
 .......................................
 | FAULT -----| EICAS LOOP 1 |
 .......................................
 | FAULT FAULT | FAIL |
 .......................................
 | -----FAULT | EICAS LOOP 2 |
 2....................…................1

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MAINTENANCE MANUAL
 (4)  A cockpit APU fire indication is given by the following: (a) The red APU fire switch handle, on the P8 control stand, lights up and unlocks. (b) The red FIRE light, on captain's instrument panel P1-3, comes
 on.
 (c) The fire warning message - APU FIRE, is displayed on EICAS (Engine Indication and Crew Alerting System - P2 panel). (d) The red master WARNING lights, on glareshield panels P7, come
 on.
 (5) (6) (7)  (e) The fire bell sounds, on the flight deck aural warning speakers. (f) The status/maintenance messages APU FIRE LP 1 and LP 2 are displayed on EICAS.An APU remote fire indication is given on P62 by the following: (a) The red APU FIRE light comes on. (b) When the airplane is on the ground and both engines are not running, the APU fire warning horn sounds.When a fire is detected, the fire alarm signal is also provided to the APU, signaling the APU to shut down. The APU fire warning horn (on P62) sounds until one of the following occurs: (a) The APU fire switch handle (on P8) is pulled out. (b) The APU FIRE SHUTDOWN switch (on P62) is pushed. (c) The fire signal ceases.AIRPLANES WITH SYSTRON DONNER FIRE DETECTORS; a dual-loop fault indication is given by the following: (a) The amber FAIL P-RESET switchlight, on the P8 control stand,
　
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