Definition
A remotely mounted sensing unit, typically installed in a wingtip or other location well away from electrical and ferrous interference, that detects the direction of the Earth's magnetic field and sends that heading information electrically to the heading indicator in the cockpit. It is the sensor element of a slaved gyro compass system, continuously correcting the directional gyro to keep it aligned with magnetic north.
Plain English
A small magnetic sensor mounted in a quiet part of the airframe that picks up which way is magnetic north and sends that signal to the heading indicator on the panel, so the gyro stays lined up with the real magnetic heading.
Context Anchor
Seen in remote indicating compass and heading indicator systems, usually as a component mounted away from metal and electrical equipment that could disturb its reading.
Derivation
Slaving' here comes from the engineering term 'slave,' meaning a device that automatically follows a master signal. The transmitter doesn't drive the system on its own — it feeds magnetic heading data to the gyro, which then 'slaves' itself to that signal.
Why Pilots Care
Without continuous correction from this unit the heading indicator will drift, producing large errors during instrument flight and complicating navigation.
Intuition Check
Do not read slaving as a manual setting. Here, slaving means the heading instrument is automatically kept in line with the magnetic sensor’s reference.
Example Sentence 1
The magnetic slaving transmitter is mounted in the wingtip to keep it away from the electrical noise and metal of the cockpit.
Example Sentence 2
If the magnetic slaving transmitter fails in flight the heading indicator may begin to precess and show an incorrect course.