Definition
Heading indicators that are automatically corrected to magnetic north by a remote magnetic sensor (a flux gate or magnetometer), eliminating the precession drift that requires manual realignment in non-slaved gyroscopic heading indicators.
Plain English
A heading indicator that fixes itself. Instead of you having to reset it every fifteen minutes to match the magnetic compass, a small sensor mounted in the wing or tail constantly senses magnetic north and keeps the indicator pointed correctly on its own.
Context Anchor
Seen in instrument flying when using heading indicators, horizontal situation indicators, or other cockpit displays that show aircraft heading.
Derivation
Slaved' comes from the engineering sense of one device being made to follow, or be controlled by, another. Here the heading indicator is 'slaved' to the magnetic sensor — it follows whatever the sensor tells it about magnetic north.
Why Pilots Care
Slaved indicators reduce pilot workload by removing the need to manually reset the heading indicator to the magnetic compass during flight.
Analogy
It is like a clock that automatically sets itself from a time signal. You still look at the clock, but another source keeps it corrected.
Intuition Check
“Slaved” does not mean the indicator is less important or manually operated. In this context, it means the indicator is automatically controlled or corrected by another source.
Example Sentence 1
Because the aircraft has slaved indicators, the pilot did not need to realign the heading indicator with the magnetic compass during cruise.
Example Sentence 2
Because the heading indicator was slaved, it did not require periodic manual alignment with the compass during the long cross-country flight.