Plain English Meaning

An older type of gyro instrument that can be knocked off-kilter if the aircraft pitches or banks too steeply. When that happens, the instrument's reading is no longer trustworthy until the gyro is reset.

Full Definition

A gyroscopic flight instrument whose gimbal travel is not mechanically restricted, allowing the gyro rotor to tumble (or 'spill') when the aircraft exceeds the instrument's normal operating limits in pitch or bank. Once spilled, the instrument gives unreliable indications until the gyro is re-erected, either automatically or by a manual caging knob.

Context Anchor

Seen in instrument flying when discussing recovery from unusual attitudes, especially when deciding which instruments can be trusted after a steep pitch or bank.