Definition
The condition of an aircraft system that has been pre-set to activate automatically when a specific triggering condition is met. The system is not yet operating, but is ready and will engage on its own without further pilot action once the trigger occurs.
Plain English
A system is armed when the pilot has set it up in advance so it will switch itself on at the right moment, instead of needing to be turned on manually when that moment arrives.
Context Anchor
Seen on aircraft switches, warning systems, safety equipment, and flight deck displays that show whether a system is ready to act.
Derivation
From the general English use of 'arm' meaning to make a device ready for action — as in arming a weapon or alarm. In aviation it carries the same idea: the system is prepared and waiting, but has not yet fired.
Why Pilots Care
Arming the wrong mode, or forgetting to arm a needed mode, is a common cause of automation surprises. A system that is armed will activate on its own — so the pilot must know what is armed, what trigger will engage it, and what the aircraft will do when it does.
Intuition Check
Do not read armed as “carrying weapons.” In aviation, armed usually means “set and ready to act,” often before anything visible happens.
Example Sentence 1
After intercepting the localizer, the pilot confirmed the approach mode was armed so the autopilot would capture the glideslope automatically.
Example Sentence 2
With the autobrakes armed, the system applied maximum braking right after touchdown.