27-51-00
 ALL  ú ú 03 Page 25 ú Jul 15/88
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
 15. Flap Asymmetry Control System_____________________________
 A.  The flap asymmetry control system stops operation of the trailing edge flaps when a specified difference exists between the position of the left and right flaps. The system consists of two-position transmitters mounted in the outboard flap drive system (Fig. 1), a dual synchro-type position indicator with comparator switch (Ref 27-58-01, D and O), and a flap asymmetry shutoff relay. (See Fig. 12 for system circuit.) An asymmetry test circuit, consisting of test switch and light mounted on the E-3 electronic equipment rack in the electronics bay, is an integral part of the position indicating system (Ref 27-58-01).
 16. Flap Takeoff Warning Switch___________________________
 A.  A flap takeoff warning switch is mounted to the flap control unit (Fig. 1). The switch is actuated by a cam mounted on the control valve follow-up drum shaft. The switch is adjusted to actuate with the flaps in a position other than the takeoff range. With the airplane on the ground and the throttle advanced, a warning horn will sound intermittently if the flaps are not in the takeoff range (Ref 31-26-00, Aural Warning Systems).
 17. Flap Load Limiter System________________________
 A.  The trailing edge flap system is protected from excessive airloads by a flap load limiter system. The load limiter system automatically retracts the flaps from 40 to 30 units when airspeed exceeds a range of 158 to 162 knots.
 B.  The load limiter system (Fig. 13) consists of the trailing edge flap control valve and solenoid valve, two airspeed switches (or two printed circuit boards comprising an ARINC 429 receiver and power supply), two flap 40-unit switches, and on some airplanes, a flap load relief light.
 C.  With the flap control lever positioned to the 40-unit detent and the airplane off the ground, the load limiter system is armed. When the airspeed switches or the ARINC 429 receiver senses an airspeed in excess of a range of 158 to 162 knots, the hydraulic solenoid valve attached to the trailing edge flap control valve is energized. Energizing the solenoid valve positions the trailing edge flap control valve to the 30-unit position, allowing pressurized fluid to flow to the hydraulic motor. As airspeed decreases to below a range of 153 to 157 knots, the solenoid valve is de-energized, the control valve is positioned to the 40-unit position, and the flaps extend to 40 units.
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 27-51-00
 ALL  ú ú 05 Page 26 ú Nov 12/99
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
 18. Airspeed Switches (On airplanes with airspeed switches)_________________
 A.  Two airspeed switches are installed in the lower compartment just below the flight compartment floor on the right side forward of the station line common to the forward bulkhead of the nose wheel well. The airspeed switch (S560) is connected to the No. 1 auxiliary pitot static system and the airspeed switch (S562) is connected to the No. 2 auxiliary pitot static system.
 19. Printed Circuit Boards (ARINC 429 Receiver) (Airplanes with ARINC 429______________________ Receiver)
 A.  Two printed circuit boards are housed within a card file assembly in the E11 landing gear logic shelf. The ARINC 429 receiver circuit board is contained within module M1453 and the power supply circuit board is contained within module M1452.
 20. Flap 40-Unit Switches_____________________
 A.  Two flap 40-unit switches are installed on the flap control quadrant. The switches are actuated with the flap control lever positioned to 40 units and complete a segment of the flap load limiter electrical circuit.
 21. Flap Control Cable Tension Switch System________________________________________
 A.  A flap control cable tension switch system (Fig. 14) is located below the cabin floor near the flap control unit quadrant. The system consists of a spring loaded cable pulley support lever, a magnet, and a reed switch. Tension on the flap control cables holds the magnet near the switch. A break in the cable allows the spring to pull the magnet away to activate the switch. The switch supplies power to close the bypass valve and shut off hydraulic power to the flap power units.
　
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