Flight behaviour of aircraft

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Aircraft instruments (part I)

Aircraft instruments are basically devices for obtaining information about the aircraft and its environment, and for presenting that information to the pilot in a concise form. Their purpose is to detect, measure, record, process and analise the variables encountered in flying an aircraft. They are mainly electrical, electronic or gyroscopic. They are concerned with the behaviour of the engines, the speed, height and attitude of the aircraft and its whereabouts.

Instruments Concerned with Flight Information

Height. An instrument for measuring and showing height above a level of reference is called an altimeter. It is basically an extremely sensitive aneroid barometer which measures static pressure at the height the aircraft is flying and, according to the difference between this and the pressure at a predetermined reference level, indicates height above reference level.

Vertical Speed. The rate of change in altitude is measured and shown by a vertical speed indicator. This indicates the speed of climb (ascent) or descent (dive or glide).

Horizontal Airspeed. Horizontal airspeed is measured and shown by an airspeed indicator (ASI). The ASI is an aneroid capsule which measures the difference between static pressure and the pressure inside an openended tube, called Pitot tube, usually situated on or underneath the nose of the aircraft.

Turning Characteristics. Aircraft turning characteristics can be measured and shown by a simple device known as a turn-bank indicator.

Attitude. The attitude of an aircraft relative to the surface of the earth is shown by an "artificial" or "gyro" horizon. There is a horizon bar on the instrument that always remains parallel to the surface of the earth.

Direction. An elementary direction-measuring instrument is a simple magnetic compass which may, however, be inaccurate by a degree or two in straight and level flight and much more inaccurate in turns.