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737-300/400/500MAINTENANCE MANUAL
Go-Around Switch Logic
(1)
The GA function of the TO/GA switches is armed when the A/T is engaged, radio altitude is less than 2000 feet (barometric altitude less than 15,000 feet if LRRA is invalid), the airplane has not been on the ground for more than two seconds, airspeed is greater than 60 knots (or 80 knots for airplanes with A/T P/N 10-62017-25 and subsequent), and the A/T is not in throttle hold mode. When the A/T GA mode armed, pressing either TO/GA switch enables GA switch logic which in turn sets the GA mode, reduced or maximum.
Reduced Go-Around Mode Logic
(1)
During reduced GA, the N1 limit is set to a value that will result in a positive rate of climb. The N1 error signal is processed through the N1 command circuit.
(2)
Reduced GA mode logic is set by the GA switch logic, if either the N1 or speed modes have been engaged since the A/T was armed for takeoff or in throttle hold. Reduced GA mode is reset if the A/T is disengaged, or if transition is made to the reduced GA (maintaining) or the maximum GA mode. When the GA timer expires, the A/T transfers to the reduced GA (maintaining) mode.
Reduced Go-Around (Maintaining)
(1)
After the GA timer has expired or the N1 is within three percent of the N1 limit, the A/T mode transfers to the reduced GA (maintaining) mode.
(2)
Reduced GA (maintaining) is reset if the A/T disengages, if maximum
GA is selected, or when the DFCS requests a mode change (speed).Maximum Go-Around Mode Logic
(1)
Maximum GA is armed one-half second after reduced GA is selected. Maximum GA is selected by pressing either TO/GA switch a second time. In maximum GA, the N1 limit is established by the Flight Management Computer.
(2)
During touch and go operation, maximum GA is armed after throttle hold during A/T takeoff. It remains armed until either N1 or speed mode is enabled or until A/T is disengaged or radio altitude is greater than 2000 feet.
(3)
Maximum GA is reset if the A/T disengages, or when the DFCS requests
a mode change.Reversion Mode Logic
(1)
If the A/T detects a failure in FMC data, the A/T will transfer to the reversion mode. In the reversion mode, the A/T authority is limited by throttle position. If the A/T attempts to enter the reversion mode during the takeoff mode, the A/T will disengage.
(2)
The reversion mode is enabled by the FMC monitor in the A/T which monitors the N1 limit data from the FMC. Reversion is enabled if the N1 limit value from the FMC exceeds the maximum N1 limit computed in the A/T, or if the data from the FMC is not valid.
Go-Around Discrete Logic
(1)
A GA discrete is provided to the DFCS to indicate to the DFCS when the GA mode cannot be terminated. This prevents a thrust reduction by the DFCS at GA initiation.
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737-300/400/500MAINTENANCE MANUAL
(2) The GA discrete is set by the transition to either reduced or maximum GA. The discrete is reset at the termination of the GA timer, if radio altitude is greater than 100 feet. The GA timer is set by entering the GA mode and is reset by time (8 seconds) or when actual N1 is within 3 percent of the N1 limit.
20. Speed/Mach Modes and Logic__________________________
A. Speed/Mach Commands (Fig. 12)
(1)
General
(a)
The speed command function processes speed or mach error or minimum speed error, or during reduced GA (maintaining), the average N1 error. The processed error, modified by equalization to minimize throttle split, provides rate commands to each servo drive.
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