The turn coordinator is one of three gyro-driven instruments in the panel of your training airplane. The turn coordinator’s gyro is mounted on a 30-degree angle upward from the longitudinal axis of the aircraft.
The turn coordinator is essentially two instruments in one. It senses rolling, yawing, and turning movements, and it displays those movements via two components: a needle that looks like an airplane and rotates right or left, and the inclinometer—a black ball suspended in liquid that rolls right, left, or remains in the middle depending on whether you are applying the correct amount of rudder during a turn. The turn coordinator is similar to the turn and bank indicator, which senses roll (but not yaw) and displays rate of turn (see “Turn and Slip Indicator,” this page).
When you turn on the airplane’s master switch, the electrical system will power up the turn coordinator’s gyro, and its warning flag should stow within about 30 seconds to let you know that it is functional. (The whirring noise you hear when you turn on the master switch is likely the gyros in the turn coordinator spinning up.) That flag, however, only signals the presence of electrical power. If the gyro stops working, the turn coordinator will fail and read incorrectly. Some turn coordinators in older aircraft are powered only by the vacuum pump.
The designation of “2 min” on the turn coordinator tells you that if you were to turn the airplane while keeping the turn coordinator wing aligned with the index, the airplane is turning at 3 degrees per second and you will perform a 360-degree turn in two minutes.