Turn and slip indicator

The gyro spins on an axis that is 90 degrees relative to the direction of the applied yaw torque force.

The torque force against the spring reaches an equilibrium and the angle that the gimbal and gyro become positioned is directly connected to the display needle, thereby indicating the rate of turn.

The hash marks are sometimes called "dog houses", because of their distinct shape on various makes of turn indicators.

Under instrument flight rules, using these figures allows a pilot to perform timed turns in order to conform with the required air traffic patterns.

Coordinated flight indication is obtained by using an inclinometer, which is recognized as the "ball in a tube".

An inclinometer contains a ball sealed inside a curved glass tube, which also contains a liquid to act as a damping medium.

The original form of the indicator is in effect a spirit level with the tube curved in the opposite direction and a bubble standing in for the ball.

In the latter case, the instrument is underdamped and in turbulence will indicate large full-scale deflections to the left and right, all of which are actually roll rate responses.

A forward slip allows a pilot to quickly drop altitude without gaining unnecessary speed, while a sideslip is one method utilized to perform a crosswind landing.

The Advisory Circular further states: "...the FAA believes, and all other commenters apparently agree...the rate-of-turn indicator is no longer as useful as an instrument which gives both horizontal and vertical attitude information."

Thus one can now legally replace a Turn-and-Slip or Turn Coordinator instrument with a second attitude indicator, preferably driven by a system different from the primary flight display.

So if the aircraft primary display is vacuum powered, the second attitude indicator should be electric, and vice-versa.