(3)
When the Vmo limit is exceeded, the mach/airspeed indicator overspeed limit switch closes to supply a ground to the aural warning clacker in the aural warning unit module. 28 volts dc is then applied to the clacker. The clacker sounds at approximately 8 Hz until the airspeed decreases below Vmo.
(4)
If the mach/airspeed indicator detects a fault condition the Vmo failure warning flag will appear in the face of the indicator and the overspeed limit switch will be inhibited from producing an overspeed warning. The following conditions will cause a Vmo fault:
(a)
No airspeed or altitude valid inputs from the digital air data computer (DADC).
(b)
Loss of electrical power to the mach/airspeed indicator.
(c)
Failure of the mach/airspeed indicator power supply.
(d)
Loss of airspeed or altitude input signal from the DADC.
(5)
When you push the MACH AIRSPEED WARNING TEST switch, the flight recorder-mach airspeed warning module supplies 28 volts dc to the overspeed limit switch in the mach/airspeed indicator. The overspeed limit switch closes and suppies a ground signal for the aural warning clacker. The clacker continues to sound as long as the test switch is pushed.
B. Control
(1)
Close No. 1 air data and mach airspeed warning system circuit breakers. Close circuit breaker for captain's mach/airspeed indicator. Make sure Vmo failure warning flag on mach/airspeed indicator does not show.
(2)
Push the MACH AIRSPEED WARNING TEST NO. 1 switch and the aural warning clacker sounds. Release the test switch to stop the clacker.
(3)
Repeat the test for system No. 2. Use the No. 2 air data and mach airspeed warning circuit breakers and first officer's mach/airspeed indicator.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
MACH AIRSPEED WARNING SYSTEM - TROUBLE SHOOTING
_______________________________________________
1. General
_______
A. These trouble-shooting procedures use the system self-test of the mach airspeed warning system No. 1. System No. 2 trouble-shooting can be done with the same procedures. Use first officer for captain and No. 2 air data and mach airspeed warning systems for the No. 1 systems.
B. If this procedure does not correct the problem, examine the wiring with the wiring diagram.
C. There are two systems installed on the airplane. The components in the two systems are interchangeable.
2. Prepare for Trouble-shooting
____________________________
A. Supply electrical power (AMM 24-22-00/201).
B. Make sure the No. 1 air data circuit breakers on panel P18 are closed.
C. Make sure the No. 2 air data circuit breakers on panel P6 are closed.
CAUTION: DO NOT ENERGIZE THE CLACKER FOR MORE THAN 5 MINUTES.
_______ PERMIT A MINIMUM OF 15 MINUTES BEFORE YOU ENERGIZE THE SYSTEM AGAIN.
3. Mach Airspeed Warning System-trouble Shooting Chart
___________________________________________________
NOTE: Refer to the Wiring Diagram manual for wiring details.
____
~............................................................................... | TROUBLE | PROBABLE CAUSE | ISOLATION PROCEDURE | REPAIR | ................................................................................. |Mach airspeed | Mach/airspeed | Make sure captain's mach/ | Replace| |aural warning | indicator | airspeed indicator Vmo | defective mach/| |clacker will | | flag is not in view. If | airspeed| |not sound | | Vmo flag is in view -| indicator| | | | | (AMM| | | | | 34-12-21/401).| | | | | | | | | Open MACH AIRSPEED circuit | Replace the| | | | breaker on P18 (P6). | defective mach/| | | | Make sure Vmo flag drops | airspeed| | | | into view. If Vmo flag | indicatior| | | | does not drop -| (AMM| | | | | 34-12-21/401).| | | | | |
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