compressibility error[kəm‚pres·ə′bil·əd·ē ‚er·ər]
The error in the readings of a differential-pressure-type airspeed indicator due to compression of the air on the forward part of the pitot tube component moving at high speeds.
An error in the airspeed indicator, which presumes that the air is incompressible. However, air is compressible and the higher the speed, the higher pressure it will indicate. An ASI (airspeed indicator) overreads because of the compressibility effect, and, so, the compressibility correction is always negative.