The gyroscopic instruments

Three instruments use spinning gyroscopes: the attitude indicator, the heading indicator and the turn coordinator (or turn-and-slip indicator). Gyros work because of rigidity in space (a spinning gyro resists changes to its orientation) and precession (a force applied to a gyro shows up 90° later in the direction of rotation).

What powers them

In many trainers, the attitude and heading indicators are driven by an engine-driven vacuum pump, and the turn coordinator is electric. That split is on purpose: if the vacuum pump fails, the electric turn coordinator still works, and vice versa. Many newer airplanes use electronic displays (glass cockpits) instead, but the backup logic is the same.

Attitude indicator

Shows pitch and bank relative to the horizon. It's the only instrument that shows both directly, and the center of your scan when flying by instruments.

Heading indicator

Shows heading without the turning and acceleration errors of the compass, but it doesn't sense magnetic north. Friction makes it precess (drift), so you align it with the magnetic compass before flight and about every 15 minutes in flight, in straight-and-level, unaccelerated flight.

Turn coordinator

The little airplane shows the rate of turn (and rate of roll). Lining the wing up with the mark shows a standard-rate turn: 3° per second, or 360° in 2 minutes. It does not show bank angle directly.

The inclinometer (the ball) shows coordination. If the ball is off to one side, add rudder on that side: "step on the ball." Ball to the inside of the turn is a slip (not enough rudder); ball to the outside is a skid (too much rudder).