Harmon Technologies, Inc.

Avionics Master Switches

The avionics master switch turns off or on power to all radios and navigation equipment at the same time.  It can be used to power off all radios before shutting down the aircraft, if it is necessary to conserve power, and any other time a quick shutdown is appropriate.  It allows maximum power to be used for tasks like engine start-up.  The main avionics master switch applies power from the normal electrical bus.  There is a second "emergency" avionics switch that powers key radios directly from the battery that could be used to maintain operation after certain types of electrical failure.

This might be a good place to note that except for starting, the engine itself needs no electrical power.  The spark for ignition is provided by a pair (for backup) of self-powered magnetos.  This is one reason why aircraft engines are much more reliable than car engines.

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