Aircraft Turn Coordinator: Definition, Parts, Function, Mechanics, Relationship

Jim Goodrich • Thu Feb 26 2026 • Reading time: 13 min

The turn coordinator is a gyroscopic aircraft instrument that combines two instruments into one and is part of the basic aircraft six-pack. It consists of a gyroscope mounted at a 30-degree angle upward in relation to the longitudinal axis of the aircraft, and it displays the rate of turn and rate of roll information. A small airplane symbol rolls right or left depending on the bank angle and the rate of turn, while a ball measures the relative strength of the force of gravity and the force of inertia caused by a turn, thereby displaying quality and coordination of the turn. Indication is achieved due to the effect of precession on the gyro inside the turn coordinator, which is usually powered by the vacuum pump. A standard rate turn is defined as an aircraft turning at 3 degrees per second.

What is a turn coordinator in aviation?

A turn coordinator combines a rate of turn indicator and a slip/skid indicator into one instrument, and it is used to determine the bank angle required for a specific rate of turn. The turn coordinator's gyro is mounted on a 30-degree angle upward from the longitudinal axis of the aircraft, and it displays the rate of turn.The turn coordinator provides feedback on the rate of roll and is part of the basic aircraft six-pack.

A turn coordinator is a gyroscopic aircraft instrument that measures the rate of roll and the coordination of a turn. It displays a miniature airplane symbol that rolls in the direction of aircraft roll, and a black ball suspended in liquid that measures the relative strength of gravity and inertia. Pilots monitor the instrument on startup and taxi to guarantee proper function. The gyroscope inside resists rotational motion through rigidity and precession. When the miniature airplane aligns with doghouse-type marks on the dial, the aircraft is making a standard rate turn. The inclinometer, located below the instrument, indicates slip or skid by deflecting the black ball outward from the turn.

What are the parts of a turn coordinator?

A turn coordinator contains two independent sub-assemblies: a gyroscopic roll-sensing unit and an inclinometer. The gyroscope is a spinning disc mounted in a single gimbal. The gimbal axis is parallel to the longitudinal axis of the aircraft, while the gyro spin axis is kept parallel to the lateral axis. Because only one gimbal is used, the gyro enjoys a single degree of freedom. A calibration spring restrains the gimbal and keeps the spin axis from precessing indefinitely. A small airplane symbol is attached to the gyro gimbal; when the aircraft banks, the gyro remains rigid in space and the airplane silhouette rolls with respect to the case, giving the pilot a direct indication of the direction and approximate rate of roll. The front glass carries dog-house-type turn alignment marks. The wing of the miniature airplane is expected to line up with those marks during a standard-rate, 2-minute turn.

The inclinometer, called the ball in the tube, is a liquid-filled curved glass that houses a black ball. The ball measures the relative strength of gravity and inertia forces: if the turn is coordinated the ball stays centered; if the aircraft is skidding the ball rolls outward, and if it is slipping the ball slides inward. A red flag appears whenever the gyro is not up to operating speed. After engine start the activation of the gyroscopes causes any flags to disappear and the unit becomes operational.

What are the types of turn coordinators?

Turn coordinators are broadly categorized into vacuum-driven and electrically-driven types. A vacuum-driven turn coordinator uses engine suction to spin a gyroscope, indicating the aircraft's rate of turn and roll quality (slip/skid) via a canted gyro. An electrically driven turn coordinator uses a DC-powered gyroscope to show the aircraft's rate of turn (yaw rate) and roll rate, indicated by a miniature airplane banking against a fixed horizon, plus a ball inclinometer for slip/skid.

How does an electric turn coordinator work?

Inside the electric turn coordinator, a gyroscope spins at about 10,000-15,000 revolutions per minute. Its spin axis is kept vertical and restrained by a calibration spring. When the aircraft yaws, the gyro experiences a torque that is 90 degrees to the yaw axis. The calibration spring warps this torque into a tilting motion so the gyro precesses 90 degrees due to the applied force. The gimbal, restrained by the spring, pivots the other way, and the little airplane symbol rolls left or right while the ball rolls right, left, or remains in the middle of the tube to show side-slip.

The inclinometer is a black ball suspended in fluid and measures the relative strength of gravity and inertia forces acting on the airplane. If the airplane symbol tilts, the miniature airplane symbol banks to match the turn. The instrument has a red flag on the right side above the miniature airplane symbol. A warning flag stows within about 30 seconds to indicate instrument functional while red flag indicates the instrument is in a non-operational status. Flags only indicate loss of power/vacuum pressure; a warning flag does not check the validity of the gyroscope.

Pilots monitor instrument performance on startup taxiing. Aircraft taxi causes the aircraft to indicate bank in the direction of taxi turns because the gyro responds to roll as well as yaw. Indication achieved due to precession effect shows 2-minutes which means a standard-rate turn held for 2 minutes, resulting in a 360 degree turn. Newer aircraft utilize IRU, INS, and AHRS systems for glass displays. AHRS uses gyroscopes and accelerometers to determine attitude-and the electric turn coordinator tells the pilot whether he is turning at a standard rate or skidding, provided the gyroscope is not invisible when it fails without flag.

I learned that an electric turn coordinator contains a gyroscope supplied by the aircraft's electrical network. The electric motor gives invariable and dependable rotation, so the gyroscope spins at a fast, steady speed. When the pilot uses aileron force to begin a turn, the gyro instantly indicates the speed of rotation, and any variance from coordinated flight is immediately shown by the inclined indicator ball. The whizzing audio shows the gyrostabilizer at work, and the pilot concentrates on the small aircraft's placement with indicator signs to maintain a standard-rate performance.
Jim Goodrich
Pilot, Airplane Broker and Founder of Tsunami Air

How does the turn coordinator needle work?

The airplane-symbol needle is part of a small gyroscope mounted at a 30-degree tilt which lets the gyro feel both roll and yaw. When the aircraft begins to bank, the gyro tries to resist the new motion. Torque is generated which pushes against an internal calibration spring, and the spring reaches equilibrium at an angle proportional to roll rate. Through a shaft and gimbal, that angle is transferred to the display, so the needle rotates right or left in proportion to the rate of turn. The farther the airplane is rolled, the greater the torque, and the farther the pointer deflects until it aligns with the dog-house-type hash marks that denote a standard-rate turn. Because the mechanism responds to roll rate rather than static bank angle, the indicator is the primary bank instrument any time the pilot is checking that the turn is being performed at the desired rate. Pitch changes, altitude, or speed do not affect the reading and only the rate of roll and yaw matter. The inclinometer, a black ball suspended in liquid, sits below the needle. It rolls right, left, or stays in the middle to show slip or skid, giving the pilot a complete picture of turn quality.

The pointer is controlled by a gyroscope specifically configured to comprehend turning about the perpendicular axis. Its motion is an immediate reaction to steering stimuli, and the pointer's movement heightens with the bank tilt. During normal rate rotations, the pointer turns and reveals the heading and nature of the movement.

How much is the turn coordinator canted?

The turn coordinator gyro is canted 30 degrees from the horizontal. The gimbal axis is canted 30 degrees upward from the transverse axis. This 30-degree tilt enables the instrument to sense roll rate as well as yaw rate. Because the gyroscope is mounted at a 30-degree angle upward in relation to the longitudinal axis of the aircraft, the rolling motion of the aircraft deflects the gyro and moves the miniature airplane symbol. The standard rate turn is calibrated to 3 degrees per second, so when the wing of the miniature airplane lines up with the standard rate marks, you are turning at 3 degrees per second, completing 360 degrees in two minutes.

What forces act on the ball in the turn coordinator?

The forces acting on the ball in the turn coordinator are gravity and centrifugal force. The inclinometer ball is suspended in a liquid that allows it to roll left or right within the curved glass tube. The liquid is merely damping fluid. It does not drive the ball but simply lets the ball respond to the real forces of flight. The ball moves as the forces of flight act on it: gravity provides a constant downward force, while centrifugal force - generated whenever the airplane is turning - pushes the ball outward opposite the direction of the turn. The two opposing forces are resolved across the curved ramp of the tube. During a coordinated turn the ball stays centered because the horizontal unit of lift equals the centrifugal force. If you are skidding through your turn, centrifugal force acts on the ball more than gravity and it rolls toward the outside. If you are slipping through the turn, gravity affects the ball more than the centrifugal force and it falls to the inside of the turn. Thus, the ball's position depends on the relative strength of gravity versus centrifugal force generated in the turn.

What causes displacement in a turn coordinator?

Displacement in a turn coordinator is caused by an increase in the bank angle. The miniature airplane marks the rate of turn because gyroscopic precession tilts the gyro and gimbal the instant the aeroplane rotates about the yaw axis and this tilt is displayed as displacement of the needle. During a coordinated turn the tilt, and therefore the indicated rate, grows with bank: displacement of the turn coordinator increases as angle of bank increases. If extreme forces are applied to the gyro, for example during abrupt manoeuvres, the gyro is displaced from its normal plane of rotation and the indications become unreliable. Restraining springs keep the gyro from tumbling off its axis, while a self-levelling mechanism thereafter uses gravity to correct the tilt at about three degrees per minute.

The ball in the sealed tube tells whether the turn is truly coordinated. Too much rudder produces excess centrifugal force over the horizontal lift unit and the result is a skidding turn that displaces the ball to the outside. Too little yaw, or insufficient centrifugal force relative to horizontal lift, produces a slipping turn that displaces the ball to the inside. Because the ball is suspended in a liquid that allows it to roll right, left, or remain in the middle, the pilot merely adds rudder pressure on the same side to which the ball slides. In single-engine aeroplanes, asymmetric thrust from the propeller disc, higher power settings and lower speeds, and spiral flow from the propeller wake all make the ball move to the right. Directional offset on the vertical fin and about half a diameter of bank toward the operating engine at Vyse are therefore built-in corrections.

What is the turn coordinator powered by?

The turn coordinator is electrically powered, receiving direct current from the aircraft's electrical system. When the master switch is turned on, the electrical system powers up the turn coordinator's gyro, and the instrument begins to operate without waiting for engine-driven suction.

In older aircraft, the turn coordinator was vacuum-driven, with an engine-driven pump creating suction to spin the gyro. However, most training aircraft now run the turn coordinator on electrical power. This arrangement provides redundancy: if the vacuum pump quits, the electrically-powered turn coordinator remains usable, assuring the pilot still has a valid indication of rate of turn and coordination. The warning flag on the instrument face will not indicate any red flags when electrical power is present, confirming reliable gyro operation.

What does the turn coordinator circuit breaker do?

The turn coordinator's white circuit breaker will pop automatically in case of a short or surge. With the breaker open, power is removed from the instrument. The pilot cannot remove power from the turn coordinator unless the circuit breaker has popped. As such, the switch for the turn coordinator is not pullable.

What is the relationship between the turn coordinator and rudder?

The turn coordinator does not measure yaw directly but senses roll and the resulting yaw rate. Inside its case a gyro precesses when the aircraft rotates about both its longitudinal and vertical axes, so the miniature airplane displayed on the face tilts in proportion to the rate of turn. Because the instrument responds to rotation rather than to sideslip, the pilot must use the inclinometer ball, not the miniature airplane, to detect uncoordinated yaw.

Rudder provides yaw control and counteracts adverse yaw. The ball moves to the inside of the turn when rudder is insufficient and to the outside when rudder is over-applied. To recenter the ball the pilot applies rudder pressure in the direction the ball is deflected. During roll-in, rudder pressure keeps the nose from yawing opposite the direction of roll, and during roll-out opposite aileron and sufficient opposite rudder keep the nose from yawing. Some aircraft need rudder only at initiation while others require it throughout the turn, and a properly rigged airplane needs no rudder during shallow or medium-bank turns. A steep turn generally requires a little top rudder to maintain coordination.

What is the difference between a turn coordinator and rate of turn indicator?

The difference between a turn coordinator and a rate-of-turn indicator is what each one is able to display. Both instruments show rate of turn, rely on a spinning gyroscope, and have an inclinometer, the black ball situated below the indicator that acts as a slip-skid indicator.

A rate-of-turn indicator provides rate-of-turn information only. Its gyroscope is rigid in space, so the pointer deflects whenever the aircraft yaws and the index at top indicates no rate of turn. Because the instrument cannot determine bank angle or roll rate, skid means the rate of turn is too great for the angle of bank, while slip means the rate of turn is too slow for the angle of bank.

A turn coordinator is built with a canted gyro. This tilt lets the miniature aeroplane react to both yaw and the first few degrees of roll, so it can be used as a backup attitude indicator even though it cannot indicate actual bank angle or roll rate precisely.