A.  The mach airspeed warning clacker is located in the aural warning module mounted under the flight engineer's table (Ref 31-26-00). When energized, the clacker emits a clacking sound interrupted at a 7 |1 Hz rate. The clacker is electrically isolated from all other systems in the aural warning module.
 7.  Mach Airspeed Warning Test Switch
_________________________________
 A.  The mach airspeed warning test switch activates the warning clacker when the system is operating properly. The test is made without interrupting any signal paths in the warning system.
 8.  Fuel Tank Relays and Fuel Level Float Switches (ON AIRPLANES WITH
______________________________________________ SUPPLEMENTARY FUEL TANKS)
 A.  The fuel tank relay, located on shelf E2-1, is energized through the fuel level float switches of supplementary fuel tanks when either fuel tank is not empty. This will energize the fuel tank airspeed warning switch, and an aural warning is provided when the airplane speed exceeds airspeed limits for operating with fuel in the reserve fuel tanks.
 9.  Operation (Fig. 2)
_________
 A.  Functional Description
 (1)  
The mach airspeed warning clacker is powered by the warning system's 28-volt dc supply. When activated, a solid-state circuit generates the tones and drives a speaker in the aural warning module creating the interrupted clacking sound. The warning clacker is normally held inactive by maintaining an open ground circuit on the clacker control.

 (2)  
The mach airspeed warning switch governs the clacker control connection described in (1) by means of the clacker control relay.

 (a)  
When de-energized, this relay grounds the clacker control and thereby activates the warning clacker. Its normal operating condition is with 28-volt dc power passing through the airspeed switch contacts to energize the relay winding. Spark suppression is provided by a resistor and diode.

 (b)  
The airspeed switch contacts are mounted on a pair of rocking shafts independently actuated by aneroid (altitude) and differential (airspeed) pressure diaphragm capsules connected to the pitot-static system. The contacts stay closed (and the clacker deactivated) as long as the aircraft remains within its maximum operating limit speed. Whenever this speed is exceeded, the contacts open, de-energizing the clacker control relay, grounding the clacker control and thereby activating the clacker.

 (3)  
Operation of the gear down dispatch airspeed warning switch is identical to the mach airspeed warning switch.

 (4)  
On airplanes with supplementary fuel tanks, the fuel tank airspeed switch is connected to the system through the fuel tank relay, parallel to the mach airspeed warning switch in NORMAL VMO mode, when either supplementary fuel tank is not empty.

 (5)  
On airplanes without supplementary fuel tanks,

 EFFECTIVITY

 
 ALL  32 Page 3  Apr 25/9634-14-00

Mach Airspeed Warning System - Simplified Schematic Diagram
Figure 2 (Sheet 2)

EFFECTIVITYAIRPLANES WITH
717 Page 5SUPPLEMENTARY FUEL TANKS
Oct 25/79
34-14-00
T33574
 the mach airspeed warning test switch is a normally open, momentary on, spring-loaded toggle switch. When held in the TEST position it places 28 volts dc on the ground side of the clacker control relay coil in the warning switch. This bias cancels the flow of current through the relay coil, the relay is de-energized and the clacker is activated.
 (6)  On airplanes with supplementary fuel tanks, the mach airspeed warning test switch is a center-off, spring loaded toggle switch. When held in the AUX (RES) FUEL position, it places 28 volts dc on the ground side of the clacker control relay coil in the warning switch if either supplementary fuel tank is not empty. This bias cancels the flow of current through the relay coil, the relay is de-energized and the clacker is activated. When held in NORM position, it activates the mach airspeed warning switch or the gear down dispatch airspeed warning switch, depending on the setting of the mach airspeed-gear down airspeed selector switch.
 B. Controls
 (1)  
The MACH WARN circuit breaker, on electrical circuit breaker panel P12, controls 28-volt dc power distribution to each portion of the mach airspeed warning system. The warning system is in continuous operation whenever there is 28 volts dc on the airplane essential bus.

 (2)  
On airplanes without supplementary fuel tanks, system controls include the circuit breaker, the mach airspeed warning test switch and the mach airspeed-gear down dispatch selector switch.
　
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