Turn and slip indicator

The turn and slip indicator (also called ‘turn and bank indicator’) and the turn coordinator (TC) variant are essentially two aircraft flight instruments in one device. The top part indicates the rate of turn, or the rate of change in the aircraft’s heading; the lower part indicates whether the aircraft is in coordinated flight, showing the slip or skid of a turn.

The display contains hash marks for the pilot’s reference during a turn. When the needle is lined up with a hash mark, the aircraft is performing a ‘standard rate turn’, which is defined as three degrees per second. This translates to two minutes per 360 degrees of turn. Indicators are marked as to their sensitivity with ‘2 min turn’.

Inclinometer

The ball in the tube is called the ‘inclinometer’. The ball gives an indication of whether the aircraft is slipping, skidding or in coordinated flight. The ball indicates the ‘quality’ of the turn, with respect to rudder-aileron coordination.

When the ball is centred in the middle of the tube, the aircraft is in coordinated flight.

If the ball is on the inside (wing down side) of a turn, the aircraft is slipping.

If the ball is on the outside (wing up side) of the turn, the aircraft is skidding.

In practice

Slipping and skidding within a turn is sometimes referred to as a ‘sloppy turn’, due to the discomfort it can cause to the pilot and passengers. When the aircraft is in a balanced turn, passengers experience gravity directly in line with their seat.

Turn coordinator

The turn coordinator is a development of the turn and slip indicator.

In contrast to the turn and slip indicator, the turn coordinator can respond to roll as well as yaw. This allows the instrument to display a change more quickly, as it will react to the change in roll before the aircraft has even begun to yaw.