Switches OFF,ON and ARMED

[Paul12 2]

I notice that many switches ( ex Emergency Power,Emergency Light ) indicate an

OFF,ON and ARMED position.

 

What does ARMED indicate as it seems to me a switch can only be on or off.

 

Thanks

 

HUbert Werni

[Tatave 57]

ARMED means that it will automatically activate when the switch's event is needed. For example, if you ARM the spoilers on a 737, the spoilers will automatically deploy on landing.

 

Another example: Have you ever accidentally turned off the engines on a complex plane (e.g the MD11) without having ground power on or the APU running? The EMERGENCY lights come on automatically if you have them armed.