FPA: flight path angle PA: pitch angle

Pitch angle is the angle between a line through the aircraft’s nose and the horizontal. By convention we call this THETA. This is what we see on the ADI. Flight path angle is the angle between the aircraft’s velocity vector and the horizontal. By convention we call this GAMMA. In the climb pitch attitude is equal to the angle of climb plus angle of attack.

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source: http://www.atpforum.eu/showthread.php?t=12207