LH ALL ATG Page 401 Aug 25/86
34-13-10
MACH AIRSPEED WARNING SYSTEM - DESCRIPTION AND OPERATION
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1. General (Fig. 1)
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A. The mach airspeed warning system provides an aural warning on the flight deck when the airplane exceeds its maximum operating limit. The warning system consists of a mach airspeed warning switch, warning clacker, and test switch. One system is installed in the airplane. In addition, a gear down dispatch airspeed switch is also installed. This switch, when selected, will provide an aural warning when the airplane speed exceeds 270 knots.
B. On airplanes with supplementary fuel tanks, a third airspeed warning switch is installed. The switch is active when either supplementary fuel tank is not empty and it will provide an aural warning whenever airspeed exceeds 342 knots.
C. Pitot and static air pressure (Ref 34-11-00, Pitot-Static System) control a pressure sensitive warning switch as a function of mach number or equivalent airspeed. When the maximum operating speed limit envelope is reached, the switch actuates a warning clacker at the flight engineer's station.
D. A test switch, located on the pilots' overhead panel P5, initiates an operational test.
E. The mach airspeed-gear down airspeed selector switch is installed. This switch allows connection of either the mach airspeed warning switch or the gear down dispatch airspeed warning switch to the clacker in the aural warning module.
F. System power is supplied from the 28-volt dc essential bus.
2. Mach Airspeed Warning Switch (Fig. 1)
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A. The mach airspeed warning switch is located on shelf E2-1 next to stanchion 3 in the main equipment center. The switch assembly contains a pressure-diaphragm operated airspeed switch and a clacker control relay.
3. Gear Down Dispatch Airspeed Switch
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A. The gear down dispatch airspeed switch is located on shelf E2-1, next to the mach airspeed warning switch, in the main equipment center. The switch assembly is functionally identical to the mach airspeed warning switch, except that the setting of the switch is fixed at 270 knots.
4. Mach Airspeed-Gear Down Airspeed Selector Switch
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A. The mach airspeed-gear down airspeed selector switch is installed near the gear down dispatch airspeed warning switch on shelf E2-1.
B. The selector switch is a two-position toggle switch. In NORMAL VMO position, the mach airspeed warning switch is connected to the system. In GEAR DOWN DISPATCH position, the gear down dispatch airspeed warning switch is connected to the system.
5. Fuel Tank Airspeed Waring Switch (ON AIRPLANES WITH SUPPLEMENTARY FUEL TANKS)
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A. The fuel tank airspeed warning switch is located on shelf E2-1, adjacent to the gear down dispatch warning switch. The switch assembly is functionally identical to the mach airspeed warning switch, except that the setting of the switch is at 342 knots.
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