What does the slip/skid indicator tell you when the bubble is off center?

• A. The aircraft is not in coordinated flight; you are in a slip or skid
• B. The airspeed is incorrect
• C. The altitude is changing rapidly
• D. The heading is off

Answer: (A)

The slip/skid indicator is all about coordination in a turn. The bubble (the ball) sits in a curved tube and centers only when the airplane is in coordinated flight, meaning the rate of turn and the yaw are balanced with proper rudder input. When the bubble is off center, you’re not coordinated—you're slipping or skidding. That off-center condition signals that there’s lateral (sideways) acceleration going on, not a change in airspeed or altitude or heading.

So the bubble being off center isn’t telling you about speed, altitude, or direction, but rather that the turn isn’t coordinated. Correct it by using the appropriate rudder to re-center the bubble and restore coordinated flight. In crosswinds or during a turn, that keeps your flight path aligned with your heading and your wings level with respect to the relative wind.