4. System Interfaces
A. Signal Interfaces
The SAC uses the following four inputs to control the Speedbrake Autostow function. These inputs already exist on Airplanes not equipped with the Autostow function.
Parameter Source
Computed Airspeed data ADC # 2's low speed ARINC 429 data bus
Gross Weight data FMC's low speed ARINC 429 data bus
Trailing Edge Flap Position data M10331 FSEU 1 Flap Up Switch and M10332 FSEU 2 Flap Up Switch
Airplane Air/Ground state P36 left misc relay panel K149 Sys1 Air/Gnd relay and K145 Sys1 Air /Gnd
B. Electrical Power Interface
The electrical power is supplied from the 28 VDC Bus 2 to the Speedbrake Autostow System, through the SAC, as shown in Figure 4. The actuator remains in its last position if electric power is lost.
5. Test Functions Maintenance Tests
The SAC has the following three ground tests for the Autostow function, which are initiated via the SAC's test bottoms panel menu.
The first test is a system test and commands the actuator to retract and then to extend. At both positions, the SAC checks for actuator response by monitoring the actuator's position switches. Also, the "Speedbrakes Do Not Arm" and “Test in Progress” lights are turned on during this test.
A. Bite Test
SAC has ground test routines that perform the following:
(1)
Checks for receipt of airspeed data from ADIRU. The test passes if label 206 is received, its parity is odd, and SSM is NCD.
(2)
Checks for receipt of gross weight data from FMC. The test passes if label 075 is received, its parity is odd, and the SSM state is “valid”.
(3)
Checks for valid T.E. flap position.
(4)
Checks for operation of the “Auto Speedbrake” light on the P11 panel, and EICAS message.
(5)
Checks for operation of the autostow actuator. The test performs the following:
(a)
Checks the actuator’s Extended position switch is True, and the Retract position switch is False.
(b)
Commands the actuator to drive to the Retract position, waits for two seconds, and then checks that the actuator’s Retract position switch is True, and the Extend position switch is false.
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757-200
MAINTENANCE MANUAL SUPPLEMENT
Part I
(c) Commands the actuator to drive to the Extend position, waits for two seconds, and then checks that the actuator’s Extend position switch is True, and the Retract position switch is false.
(6) Commands the Autostow actuator to the Retract position and holds it there for handle forces checks.
B. Fault Isolation
A speed brake autostow function fault is stored in SAC NV for all flight deck effects. A fault is stored anytime SAC illuminates the Auto Speedbrake light on the P11 panel, except during maintenance.
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