Definition
A mode of operation in which a system performs part of its function automatically but still requires a human action to start, stop, or guide the process. The machine handles the mechanical or sequential steps once initiated, but it does not run entirely on its own.
Plain English
The equipment does most of the work by itself, but a person still has to start it, stop it, or step in at certain points.
Context Anchor
Seen in aircraft system descriptions, operating instructions, and maintenance procedures where a system is partly automatic but still needs human action.
Derivation
From the Latin 'semi-' meaning 'half,' and 'automatic,' meaning 'self-acting.' So semiautomatic literally means 'half self-acting' -- the system does part of the job on its own, but not all of it.
Why Pilots Care
Knowing a system is semiautomatic tells the pilot they are still in the loop. They must initiate, monitor, or finish the action -- the system will not handle the entire task without input.
Intuition Check
Do not read “semiautomatic” as “automatic enough that I can ignore it.” It means the system helps, but it still requires a human action at some point.
Example Sentence 1
The fuel transfer system uses a semiautomatic operation, so the pilot selects the tank and the system handles the actual transfer.
Example Sentence 2
During the preflight check the crew tested the hydraulic pumps in semiautomatic operation to confirm pressure built without continuous manual switching.