Plain English Meaning
Separate record books for certain aircraft components that have their own maintenance history, kept apart from the main airframe and engine records.
Full Definition
Maintenance records kept for individual aircraft appliances — such as propellers, magnetos, autopilots, or emergency locator transmitters — documenting their installation, inspections, repairs, overhauls, and time in service separately from the airframe and engine logbooks.
Context Anchor
Seen during preflight assessment when reviewing aircraft records before deciding whether the airplane is legal and safe to fly.