CFI Instrument Practical Test Standards, FAA-S-8081-9B, June 2001

II. Technical Subject Areas

A. Aircraft Flight Instruments and Navigation Equipment

1. Flight instrument systems and their operating characteristics
   
   
   b. Attitude indicator (attitude instrument, AI, artificial horizon, gyro horizon)
   1)Takes advantage of one of the principle properties of the gyroscope: rigidity in space
   2) Operating mechanism: small brass wheel (gyroscope) with a vertical spin axis
   a) Spun at high speed by either
   i) Stream of air (via vacuum system), or
   ii) Electric motor
   b) Mounted in a double gimbal with axes perpendicular to gyro spin axis allowing free motion in two planes around the gyro (pitch and roll)
   
   3) Horizon disk fixed to gimbals remains in same plane as gyro
   a) Blue top half and brown bottom half represent sky and ground, respectively
   b) Pitch marks indicate degree of up or down pitch
   c) Bank index indicates bank angle
   4) Symbolic aicraft is mounted on instrument case over horizon disk
   a) Knob allows pilot to raise or lower aircraft symbol to compensate for pitch trim changes
   b)Width of wings and center dot represent approximately 2 degrees of pitch change
   5) Erection mechanism inside case applies a corrective force any time gyro tilts from the vertical
   6) Older gyros tumbled at extremes of pitch (60 degrees) or roll (100 degrees), and so had a caging mechanism to lock gyro in vertical plane during such maneuvers
   7) After engine start-up, it takes two or three to as long as five minutes for gyro self-erecting mechanism to be fully effective
   8) Errors
   a) Slight nose up or down during rapid acceleration or deceleration respectively
   b) Possible small bank and pitch errors after 180 degree turn
   c) Errors are small and correct themselves within a minute or so in SLF

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