Definition
A backup turn coordinator instrument powered independently from the aircraft's primary electrical or vacuum system, used to display rate of turn and quality of turn (coordination) if the primary attitude or turn instruments fail. In modern glass-cockpit aircraft, it serves as part of the standby instrument suite that provides essential flight reference information during a primary system failure or unusual attitude.
Plain English
A spare turn instrument that keeps working when the main instruments fail, so the pilot can still tell how fast the aircraft is turning and whether the turn is balanced.
Context Anchor
Seen in instrument flying and unusual-attitude recovery, especially when a pilot must use backup instruments after losing reliable primary attitude information.
Derivation
"Standby" comes from the nautical phrase meaning "ready to act if needed" -- something held in reserve. In aviation it labels any instrument that stays available as a backup when the primary system fails.
Why Pilots Care
Maintains awareness of turn direction and coordination after loss of primary flight instruments, allowing continued control in instrument conditions until visual flight can be restored.
Intuition Check
Do not read standby as unimportant or optional. Here it means a backup instrument that is ready to use when the primary source is lost or suspect.
Example Sentence 1
After the attitude indicator tumbled, the pilot transitioned to the standby turn coordinator to keep the wings level while declaring an emergency.
Example Sentence 2
The instructor pointed to the standby turn coordinator to verify coordination while the student practiced partial-panel flying.