3.  Interface Monitors
A.  Air/Ground Position Switches
The SAC monitors two air/ground switches.  If the two inputs disagree when computed airspeed data indicates airspeed is above 185 knots, then the air/ground data is declared invalid and the internal logic defaults to an in air state. The Speedbrake Autostow System is enabled, and the "Autostow Fault" LED on the module is illuminated.
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B. T.E. Flap Position Switches
The SAC monitors two T.E. flap switches.  If the two inputs disagree, then the “Autostow Fault” LED on the module is illuminated.  Each individual flap switch state is checked on an air-to-ground transition.  If the flap input indicates flaps up, the input is declared invalid and the “Autostow Fault” LED on the module is illuminated.  If both flaps inputs are declared invalid, the internal logic defaults to a flaps up state.  The Speedbrake Autostow System is enabled, and the Autostow Speedbrake indication is turned on in the Flight Deck.
C. Actuator Position Switches
The SAC monitors two position switches from the Autostow Actuator.  If the two feedback inputs disagree with the computed autostow command, then a retracted fault or extended fault is declared.  The “Speedbrakes Do Not Arm” LED on the SAC module is illuminated.  The Speedbrake Autostow System is enabled, and the Autostow Speedbrake indication on the P11 panel is turned on, plus indication on EICAS.
D. ARINC 429 Inputs
The SAC monitors its ARINC 429 buses for activity, correct label, correct sign-status matrix, and correct parity.
If computed airspeed data is not received or is invalid, then the Speedbrake Autostow function is disabled and the Autostow Speedbrake indication is turned on.
If gross weight data is not received or is invalid, then for the Speedbrake Autostow function, the SAC defaults to gross weight above 221,000 pounds for the airplane. Autostow will activate when airspeed is above 330 knots.
E. Flight Deck Interface
The flight deck interfaces for Speedbrake Autostow System are the speedbrake handle and the Autostow Speedbrake indication and EICAS message, located on the P11 panel in the crew compartment.
F. Speedbrake Handle
The speedbrake handle provides an indication of Autostow-induced speedbrake retraction.  The Autostow-retract position (1/2 of the flight detent) is indicated on the control stand's light plate, next to the speedbrake lever, by marking "50%", reference Figure 1, 2.
There is no crew indication if Autostow does not cause the speedbrakes to retract, which occurs if Autostow activates when the speedbrakes lever's position is less than 50% of the flight detent.
The Speedbrake Autostow is an automatic function; there is no crew interface to operate the system. The speedbrake handle provides the flight crew a means to override the Autostow function, by manually extending the speedbrakes.  
　
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