Turn Coordinator

Turn Coordinator


  • Turn Coordinators display the rate of turn and roll information, as well as quality and coordination of the turn
  • Turn & slip indicators only show rate of turn
  • Developed from the turn and bank indicator
  • This ball measures the relative strength of the force of gravity and the force of inertia caused by a turn
  • Gyroscopically driven using the principle of precession
  • A line indicates the standard rate turn
  • Mounted with about a 30 - 35° canted on the gyro
  • The gyro is mounted in a single gimbal with its spin axis parallel to the lateral axis of the aircraft and the axis of the gimbal parallel with the longitudinal axis
  • Slip: rate of turn is too slow for the angle of bank
  • Skid: rate of turn is too great for the angle of bank

Turn Coordinator Construction:

  • Turn Coordinator
  • Turn coordinators provide their readings with a gyroscope, mounted at a 30° angle
  • The gyro is either electrically or vacuum driven
  • When the aircraft yaws, or rotates about its vertical axis, it produces a force in the horizontal plane that, due to precession, causes the gyro and its gimbal to rotate about the gimbal's axis
  • It is restrained in this rotation plane by a calibration spring; it rolls over just enough to cause the pointer to deflect until it aligns with one of the doghouse-shaped marks on the dial, when the aircraft is making a standard rate turn
  • A red flag shows the instrument is in a non-operational status
  • Inclinometer is located below the instrument used to determine quality of a turn (angle of bank and the rate of yaw)
  • The words printed 2-minutes means a standard rate turn held for 2-minutes would result in a 360 degree turn

Standard Rate Turns:

  • When the miniature aircraft (or the needle is straight up and down), the aircraft is straight and level
  • When the miniature aircraft (or needle) is aligned with one of the turn alignment marks, it is in a standard rate turn
  • A standard rate turn is defined as an aircraft turning at 3° per second
  • This standard turn rate is dependent upon True Airspeed and so the faster an aircraft is moving, the more angle of bank is required to achieve this set 3° rate
  • SRT Angle of Bank = [True Airspeed in Knots / 10] + 5

Turn & Slip Indicator:

  • Turn Coordinator
    Turn and Slip Indicator
  • The turn and slip indicator is an older design, and provides rate of turn and roll information [Figure 2]
    • Because the gyro is mounted along the aircraft's longitudinal axis, yaw and roll information are not provided

Preflight Actions:

  • Should indicate a bank in the direction of taxi turns
  • The ball should deflect outward from the turn

Turn Coordinator Instrument Failures:

Inertial Reference Unit (IRU), Inertial Navigation System (INS), and Attitude Heading Reference System (AHRS)

  • IRUs are self-contained systems comprised of gyros and accelerometers that provide aircraft attitude (pitch, roll, and heading), position, and velocity information in response to signals resulting from inertial effects on system components
    • Once aligned with a known position, IRUs continuously calculate position and velocity. IRU position accuracy decays with time
    • This degradation is known as "drift"
  • INSs combine the components of an IRU with an internal navigation computer
    • By programming a series of waypoints, these systems will navigate along a predetermined track
  • AHRSs are electronic devices that provide attitude information to aircraft systems such as weather radar and autopilot, but do not directly compute position information
  • Aircraft equipped with slaved compass systems may be susceptible to heading errors caused by exposure to magnetic field disturbances (flux fields) found in materials that are commonly located on the surface or buried under taxiways and ramps
    • These materials generate a magnetic flux field that can be sensed by the aircraft's compass system flux detector or "gate", which can cause the aircraft's system to align with the material's magnetic field rather than the earth's natural magnetic field
    • The system's erroneous heading may not self-correct
    • Prior to take off pilots should be aware that a heading misalignment may have occurred during taxi
    • Pilots are encouraged to follow the manufacturer's or other appropriate procedures to correct possible heading misalignment before take off is commenced


  • Always keep in mind the effects of parallax error
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