Definition
An erratic, uncontrolled spinning of a gyroscope's rotor or gimbals that occurs when the gyro is forced past its mechanical limits, causing the instrument to give false or unusable indications until it is reset or re-erected.
Plain English
When a spinning instrument inside the panel gets pushed too far and loses its bearings, so the needle swings wildly and stops showing useful information.
Context Anchor
Seen in discussions of gyroscopic instruments, including the turn-and-slip indicator and other instruments that use a spinning gyro to sense aircraft movement.
Derivation
From the everyday sense of 'tumble' meaning to fall or roll over uncontrollably. The word captures what happens inside the instrument: the gyro stops spinning smoothly on its axis and rolls around on its mounts.
Why Pilots Care
A tumbled indicator gives false turn information, forcing the pilot to cross-check other instruments until the gyro recovers.
Analogy
It is like a spinning top that gets bumped hard enough to wobble out of its steady spin. Once that happens, you cannot use its motion as a reliable guide until it steadies again.
Intuition Check
Tumbling does not mean the airplane itself is necessarily flipping over. Here it means the instrument’s internal gyro has been forced out of its normal working position.
Example Sentence 1
Older attitude indicators could tumble if the aircraft exceeded 60 degrees of pitch or 100 degrees of bank.
Example Sentence 2
After recovering from the unusual attitude, the instructor waited for the tumbled instrument to re-erect before continuing the lesson.