When autostow system extends the actuator, the speedbrake lever remains stationary; it does not move to its position prior to the Autostow actuator retraction.
The Speedbrake Autostow actuator's operating time, to either retract or extend is one second after receiving command from SAC.
If the Speedbrake Autostow actuator fails to retract when the function is “Enabled”, then the “ Auto Speedbrake Indication” on the P11 panel and an EICAS indication will illuminate. This annunciation is needed to alert the flight crew that a non-normal crew procedure needs to be followed.
Aviation Partners Boeing
757-200
MAINTENANCE MANUAL SUPPLEMENT
Part I
D. Autostow System Schematic
Figure 4 is a schematic of the Speedbrake Autostow System. It shows the following: (See aircraft specific supplement to the Wiring Diagram Manual, AP57.2-0615, for complete information on specific airplane variations.)
.
Wiring interface between components
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Wire size
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Separation codes
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Type of wiring (non-shielded)
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Source of 28 VDC
Figure 5 is a block diagram of the SAC internal structure.
E. Control Law
The SAC's control law for the Speedbrake Autostow function is shown in Figure 6. The function is computed asynchronously, with a maximum transport delay from input to computed command of 500 milliseconds.
F. Speedbrake Do Not Arm Logic
The Do Not Arm light logic is shown in Figure 7. The logic shows the various system failures, which illuminate the Do Not Arm light.
G. Autostow System Wiring Diagram
The Autostow System Wiring Diagram is shown in Figures 13A,13B,13C and 13D. See APB supplement to the Wiring Diagram Manual, AP57.2-0615, for complete information on specific airplane variation.) Information in the Wiring Diagram and its Supplement supercedes information contained in these figures.
2. Major Components
A. Speed brake Handle Autostow Mechanism
Figure 8 shows the installation of the Speedbrake Autostow Mechanism, and Figure 9 shows the mechanism in both the Disabled and Enabled states. The retract mechanism is located below the control stand.
The actuator is a linear device, powered by a 28 VDC motor. The actuator cannot be back driven.
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