Definition
A gyroscope that is not slaved or corrected to any external reference such as the Earth's magnetic field. Once spun up and set, it holds its position in space and any indication it provides drifts over time as the Earth rotates and as small mechanical errors accumulate, requiring periodic manual realignment by the pilot.
Plain English
A spinning gyro that holds whatever direction it was set to, with nothing automatically keeping it aligned. The pilot has to reset it every so often because it slowly drifts off.
Context Anchor
Seen in remote indicating compass systems when the heading indicator is operated without automatic correction from the aircraft’s magnetic sensor.
Derivation
‘Free’ here means ‘not tied to’ or ‘not corrected by’ an outside reference. The gyro is left to spin on its own without any signal forcing it back into alignment with magnetic north.
Why Pilots Care
A free gyro will drift, so the heading it shows becomes less accurate the longer you fly without resetting it. Pilots using a free gyro heading indicator must check it against the magnetic compass and realign it regularly, typically every 15 minutes, to avoid navigating off a wrong heading.
Intuition Check
“Free” does not mean the gyro is more accurate or independent of all error. Here it means the gyro is not being automatically kept in line with the magnetic heading source.
Example Sentence 1
Because the heading indicator was operating as a free gyro, the pilot reset it to match the magnetic compass every 15 minutes.
Example Sentence 2
When the remote compass transmitter senses a heading change, it applies a small torque to the free gyro to update the displayed heading.