- Absolute altitude
- Height above the ground directly below the aircraft. See the altimeter.
- Altimeter setting
- The local sea-level pressure, set in the altimeter’s window with its knob, so the altimeter shows height above sea level. See the altimeter.
- Aneroid wafer
- A sealed, thin metal capsule that expands as the outside pressure falls. A stack of them drives the altimeter.
- Bank
- How far the wings are tilted from level, in degrees.
- Calibrated airspeed (CAS)
- Indicated airspeed corrected for errors in the instrument and in how it is fitted to the aircraft. See the airspeed indicator.
- Calibrated leak
- The small hole in a vertical speed indicator that lets static air into its case slowly. It is what makes the instrument work, and why it lags. See the vertical speed indicator.
- Density altitude
- Pressure altitude corrected for non-standard temperature. It is the altitude the aircraft performs as if it were at.
- Ground speed (GS)
- Speed over the ground: true airspeed corrected for wind.
- Gyroscope
- A fast-spinning wheel that keeps pointing the same way. The attitude indicator, heading indicator and turn coordinator are gyro instruments.
- Inclinometer
- The ball in a curved tube of liquid under the turn coordinator. It shows whether a turn is balanced. See the turn coordinator.
- Indicated altitude
- What the altimeter reads with the current altimeter setting.
- Pitch
- How far the nose is above or below the horizon, in degrees.
- Pitot tube
- A forward-facing tube that catches ram air pressure for the airspeed indicator. See the airspeed indicator.
- Pitot-static instruments
- The airspeed indicator, altimeter and vertical speed indicator: the three instruments driven by air pressure.
- Precession
- The slow drift of a gyro away from where it was set, mostly from friction. It is why the heading indicator must be reset from the compass. See the heading indicator.
- Pressure altitude
- What the altimeter reads with the standard setting, 29.92 inches of mercury, set.
- Rigidity in space
- A spinning gyro’s habit of keeping pointing the same way, however the case around it moves.
- Six-pack
- Pilots’ name for the six basic flight instruments, set out in two rows of three. See Learn.
- Skid
- An unbalanced turn with too much rudder for the bank. The ball moves to the outside of the turn. See the turn coordinator.
- Slip
- An unbalanced turn with too little rudder for the bank. The ball moves to the inside of the turn. See the turn coordinator.
- Standard-rate turn
- A turn of 3 degrees a second: a full circle in 2 minutes. See the turn coordinator.
- Static port
- A small hole on the side of the aircraft that feels the still outside air pressure. The altimeter, vertical speed indicator and airspeed indicator use it.
- Suction gauge
- The gauge that shows whether the vacuum system is working.
- True airspeed (TAS)
- Real speed through the air: calibrated airspeed corrected for altitude and non-standard temperature. See the airspeed indicator.
- True altitude
- Real height above mean sea level.
- Vacuum system
- An engine-driven pump that pulls air through the gyro instruments to spin them. In most light aircraft it drives the attitude and heading indicators.
- VS0
- Stall speed in the landing setup, flaps fully down: the bottom of the white arc. See the airspeed indicator.